Guide to Space Archives

January 30, 2018January 30, 2018 by Fraser Cain

What’ll It Take to Find Life? Searching the Universe for Biosignatures

An artist's interpretation of HD 189733. It looks nice and blue, but it's actually a nightmare world that could be raining glass with 2 km/s winds. Credit: ESO/M. Kornmesser

The supertelescopes are coming, enormous ground and space-based observatories that’ll let us directly observe the atmospheres of distant worlds. We know there’s life on Earth, and our atmosphere tells the tale, so can we do the same thing with extrasolar planets? It turns out, coming up with a single biosignature, a chemical in the atmosphere that tells you that yes, absolutely, there’s life on that world, is really tough.

I’ve got to admit, I’ve been pretty bad for this in the past. In old episodes of Astronomy Cast and the Weekly Space Hangout, even here in the Guide to Space, I’ve said that if we could just sample the atmosphere of a distant world, we could say with conviction if there’s life there.

Just detect ozone in the atmosphere, or methane, or even pollution and you could say, “there’s life there.” Well, future Fraser is here to correct past Fraser. While I admire his naive enthusiasm for the search for aliens, it turns out, as always, things are going to be more difficult than we previously thought.

Astrobiologists are actually struggling to figure out a single smoking gun biosignature that could be used to say there’s life out there. And that’s because natural processes seem to have clever ways of fooling us.

What are some potential biosignatures, why are they problematic, and what will it take to get that confirmation?

Let’s start with a world close to home: Mars.

For almost two decades, astronomers have detected large clouds of methane in the atmosphere of Mars. Here on Earth, methane comes from living creatures, like bacteria and farting cows. Furthermore, methane is easily broken down by sunlight, which means that this isn’t ancient methane leftover from billions of years ago. Some process on Mars is constant replenishing it.

But what?

Well, in addition to life, methane can form naturally through volcanism, when rocks interact with heated water.

NASA tried to get to the bottom of this question with the Spirit and Opportunity rovers, and it was expected that Curiosity should have the tools on board to find the source of the methane.

Panoramic image of the Curiosity rover, from September 2016. The pale outline of Aeolis Mons can be seen in the distance. Credit: NASA/JPL-Caltech/MSSS

Over the course of several months, Curiosity did detect a boost of methane down there on the surface, but even that has led to a controversy. It turns out the rover itself was carrying methane, and could have contaminated the area around itself. Perhaps the methane it detected came from itself. It’s also possible that a rocky meteorite fell nearby and released some gas that contaminated the results.

The European Space Agency’s ExoMars mission arrived at Mars in October, 2016. Although the Schiaparelli Lander was destroyed, the Trace Gas Orbiter survived the journey and began mapping the atmosphere of Mars in great detail, searching for places that could be venting methane, and so far, we don’t have conclusive results.

In other words, we’ve got a fleet of orbiters and landers at Mars, equipped with instruments designed to sniff out the faintest whiff of methane on Mars.

Artist’s impression visualising the separation of the ExoMars entry, descent and landing demonstrator module, Schiaparelli, from the Trace Gas Orbiter (TGO). Credit: ESA

There’s some really intriguing hints about how the methane levels on Mars seem to rise and fall with the seasons, indicating life, but astrobiologists still don’t agree.

Extraordinary claims require extraordinary evidence and all that.

Some telescopes can already measure the atmospheres of planets orbiting other stars. For the last decade, NASA’s Spitzer Space Telescope has been mapping out the atmospheres of various worlds. For example, here’s a map of the hot jupiter HD 189733b

Spitzer temperature map of HD 189733b (NASA)

. The place sucks, but wow, to measure an atmosphere, of another planet, that’s pretty spectacular.

They perform this feat by measuring the chemicals of the star while the planet is passing in front of it, and then measure it when there’s no planet. That tells you what chemicals the planet is bringing to the party.

They also were able to measure the atmosphere of HAT-P-26b, which is a relatively small Neptune-sized world orbiting a nearby star, and were surprised to find water vapor in the atmosphere of the planet.

Does that mean there’s life? Wherever we find water on Earth we find life. Nope, you can totally get water without having life.

When it launches in 2019, NASA’s James Webb Space Telescope is going to take this atmospheric sensing to the next level, allowing astronomers to study the atmospheres of many more worlds with a much higher resolution.

Illustration showing the possible surface of TRAPPIST-1f, one of the newly discovered planets in the TRAPPIST-1 system. Credits: NASA/JPL-Caltech

One of the first targets for Webb will be the TRAPPIST-1 system with its half-dozen planets orbiting in the habitable zone of a red dwarf star. Webb should be able to detect ozone, methane, and other potential biosignatures for life.

So what will it take to be able to view a distant world and know for sure there’s life there.

Astrobiologist John Lee Grenfell from the German Aerospace Centre recently created a report, going through all the exoplanetary biosignatures that could be out there, and reviewed them for how likely they were to be an indication of life on another world.

The first target will be molecular oxygen, or O2. You’re breathing it right now. Well, 21% of every breath, anyway. Oxygen will last in the atmosphere of another world for thousands of years without a source.

It’s produced here on Earth by photosynthesis, but if a world is being battered by its star, and losing atmosphere, then the hydrogen is blown off into space, and molecular oxygen can remain. In other words, you can’t be certain either way.

How about ozone, aka O3? O2 is converted into O3 through a chemical process in the atmosphere. It sounds like a good candidate, but the problem is that there are natural processes that can produce ozone too. There’s an ozone layer on Venus, one on Mars, and they’ve even been detected around icy moons in the Solar System.

There’s nitrous oxide, also known as laughing gas. It’s produced as an output by bacteria in the soil, and helps contribute to the Earth’s nitrogen cycle. And there’s good news, Earth seems to be the only world in the Solar System that has nitrous oxide in its atmosphere.

But scientists have also developed models for how this chemical could have been generated in the Earth’s early history when its sulfur-rich ocean interacted with nitrogen on the planet. In fact, both Venus and Mars could have gone through a similar cycle.

In other words, you might be seeing life, or you might be seeing a young planet.

Ligeia Mare, shown in here in data obtained by NASA’s Cassini spacecraft, is the second largest known body of liquid on Saturn’s moon Titan. It is filled with liquid hydrocarbons, such as ethane and methane, and is one of the many seas and lakes that bejewel Titan’s north polar region. Credit: NASA/JPL-Caltech/ASI/Cornell

Then there’s methane, the chemical we spent so much time talking about. And as I mentioned, there’s methane produced by life here on Earth, but it’s also on Mars, and there are liquid oceans of methane on Titan.

Astrobiologists have suggested other hydrocarbons, like ethane, isoprene, but these have their own problems too.

What about the pollutants emitted by advanced civilizations? Astrobiologists call these “technosignatures”, and they could include things like chlorofluorocarbons, or nuclear fallout. But again, these chemicals would be hard to detect light years away.

Astronomers have suggested that we should search for dead earths, just to set a baseline. These would be worlds located in the habitable zone, but clearly life never got going. Just rock, water and a non-biologically created atmosphere.

The problem is that we probably can’t even figure out a way to confirm that a world is dead either. The kinds of chemicals you’d expect to see in the atmosphere, like carbon dioxide could be absorbed by oceans, so you can’t even make a negative confirmation.

One method might not even involve scanning atmospheres at all. The vegetation here on Earth reflects back a very specific wavelength of light in the 700-750 nanometer region. Astrobiologists call this the “red edge”, because you’ll see a 5X increase in reflectivity compared to other surfaces.

Although we don’t have the telescopes to do this today, there are some really clever ideas, like looking at how the light from a planet reflects onto a nearby moon, and analyze that. Searching for exoplanet earthshine.

In fact, back in the Earth’s early history, it would have looked more purple because of Archaean bacteria.

There’s a whole fleet of spacecraft and ground observatories coming online that’ll help us push further into this question.

ESA’s Gaia mission is going to map and characterize 1% of the stars in the Milky Way, telling us what kinds of stars are out there, as well as detect thousands of planets for further observation.

A conceptual image of the Transiting Exoplanet Survey Satellite. Image Credit: MIT — A conceptual image of the Transiting Exoplanet Survey Satellite.
Image Credit: MIT

The Transiting Exoplanet Space Survey, or TESS, launches in 2018, and will find all the transiting Earth-sized and larger exoplanets in our neighborhood.

The PLATO 2 mission will find rocky worlds in the habitable zone, and James Webb will be able to study their atmospheres. We also talked about the massive LUVOIR telescope that could come online in the 2030s, and take these observations to the next level.

And there are many more space and ground-based observatories in the works.

As this next round of telescopes comes online, the ones capable of directly measuring the atmosphere of an Earth-sized world orbiting another star, astrobiologists are going to struggling to find a biosignature that provides a clear sign there’s life there.

Instead of certainty, it looks like we’re going to have the same struggle to make sense of what we’re seeing. Astronomers will be disagreeing with each other, developing new techniques and new instruments to answer unsolved questions.

It’s going to take a while, and the uncertainty is going to be tough to handle. But remember, this is probably the most important scientific question that anyone can ask: are we alone in the Universe?

The answer is worth waiting for.

Source: John Lee Grenfell: A Review of Exoplanetary Biosignatures.

Hat tip to Dr. Kimberly Cartier for directing me to this paper. Follow her work on EOS Magazine.

January 8, 2018January 8, 2018 by Tammy Plotner

Messier 65 – the NGC 3623 Intermediate Spiral Galaxy

Hubble image of the intermediate spiral galaxy known as Messier 65, which is located in the Leo constellation. Credit: ESA/Hubble & NASA

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the intermediate spiral galaxy known as Messier 65.

In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects he initially mistook for comets. In time, he would come to compile a list of approximately 100 of these objects, hoping to prevent other astronomers from making the same mistake. This list – known as the Messier Catalog – would go on to become one of the most influential catalogs of Deep Sky Objects.

One of these objects is the intermediate spiral galaxy known as Messier 65 (aka. NGC 3623), which is located about 35 million light-years from Earth in the Leo constellation. Along with with Messier 66 and NGC 3628, it is part of a small group of galaxies known as the Leo Triplet, which makes it one of the most popular targets among amateur astronomers.

Description:

Enjoying life some 35 million light years from the Milky Way, the group known as the “Leo Trio” is home to bright galaxy Messier 65 – the westernmost of the two M objects. To the casual observer, it looks like a very normal spiral galaxy and thus its classification as Sa – but M65 is a galaxy which walks on the borderline. Why? Because of close gravitational interaction with its nearby neighbors. Who can withstand the draw of gravity?!

*The Messier 65 intermediate spiral galaxy. Credit: ESO/INAF-VST/OmegaCAM/Astro-WISE/Kapteyn Institute*

Chances are very good that Messier 65 is even quite a bit larger than we see optically as well. As E. Burbidge (et al) said in a 1961 study:

“A fragmentary rotation-curve for NGC 3623 was obtained from measures of the absorption features Ca ii X 3968 and Na I X 5893 and the emission lines [N ii] X 6583 and Ha. The measures from two outer regions are discordant if only circular velocities are assumed, and it is concluded that the measured velocity of one of these regions-the only prominent H ii region in the galaxy-has a large non-circular component. The approximate mass derived from the velocity in the outer arm relative to the center is 1.4 X 1011 M0. It is concluded that the total mass is larger than this, perhaps between 2 and 3 X 1011 M0. This would suggest that the mass-to-light ratio in solar units (photographic) for this galaxy, which is intermediate in type between Sa and Sb, lies between 10 and 20.”

But just how much interaction has been going on between the three galaxies which coexist so closely? Sometimes it takes things like studying in multicolor photometry data to understand. As Zhiyu Duan of the Chinese Academy of Sciences Astronomical Observatory indicated in a 2006 study:

“By comparing the observed SEDs of each part of the galaxies with the theoretical ones generated by instantaneous burst evolutionary synthesis models with different metallicities (Z = 0.0001, 0.008, 0.02, and 0.05), two-dimensional relative age distribution maps of the three galaxies were obtained. NGC 3623 exhibits a very weak age gradient from the bulge to the disk. This gradient is absent in NGC 3627. The ages of the dominant stellar populations of NGC 3627 and NGC 3628 are consistent, and this consistency is model independent (0.5-0.6 Gyr, Z = 0.02), but the ages of NGC 3623 are systematically older (0.7-0.9 Gyr, Z = 0.02). The results indicate that NGC 3627 and NGC 3628 have undergone synchronous evolution and that the interaction has likely triggered starbursts in both galaxies. The results indicate that NGC 3627 and NGC 3628 have undergone synchronous evolution and that the interaction has likely triggered starbursts in both galaxies. For NGC 3623, however, the weak age gradient may indicate recent star formation in its bulge, which has caused its color to turn blue. Evidence is found for a potential bar existing in the bulge of NGC 3623, and my results support the view that NGC 3623 does interact with NGC 3627 and NGC 3628.”

*Messier 65, as imaged by the Hubble Space Telescope. Credit: NASA,/ESA/Hubble Space Telescope*

So, let’s try looking at things in a slightly different color – integral-field spectroscopy. As V.L. Afanasiev (et al) said in a 2004 study:

“The mean ages of their circumnuclear stellar populations are quite different, and the magnesium overabundance of the nucleus in NGC 3627 is evidence for a very brief last star formation event 1 Gyr ago whereas the evolution of the central part of NGC 3623 looks more quiescent. In the center of NGC 3627 we observe noticeable gas radial motions, and the stars and the ionized gas in the center of NGC 3623 demonstrate more or less stable rotation. However, NGC 3623 has a chemically distinct core – a relic of a past star formation burst – which is shaped as a compact, dynamically cold stellar disk with a radius of ?250-350 pc which has been formed not later than 5 Gyr ago.”

Now, let’s take a look at that gas – and the properties for the gases that exist and co-exist in the galactic trio. As David Hogg (et al) explained in a 2001 study:

“We have studied the distribution of cool, warm, and hot interstellar matter in three of the nearest bright Sa galaxies. New X-ray data for NGC 1291, the object with the most prominent bulge, confirm earlier results that the ISM in the bulge is dominated by hot gas. NGC 3623 has a lesser amount of hot gas in the bulge but has both molecular gas and ionized hydrogen in the central regions. NGC 2775 has the least prominent bulge; its X-ray emission is consistent with an origin in X-ray binary stars, and there is a strict upper limit on the amount of molecular present in the bulge. All three galaxies have a ring of neutral hydrogen in the disk. NGC 3623 and NGC 2775 each have in addition a molecular ring coincident with the hydrogen ring. We conclude that even within the morphological class Sa there can be significant differences in the gas content of the bulge, with the more massive bulges being likely to contain hot, X-ray–emitting gas. We discuss the possibility that the X-ray gas is part of a cooling flow in which cool gas is produced in the nucleus.”

*The Leo Triplet, with M65 at the upper right, M66 at the lower right, and NGC 3628 at the upper left. Credit: Scott Anttila. Credit: Wikipedia Commons/Anttler*

Even more studies have been done to take a look a disc properties associated with M65. According to M. Bureau (et al);

“NGC 3623 (M 65) is another highly-inclined galaxy in the Leo group, but it is of much later type than NGC 3377, SABa(rs). It is part of the Leo triplet with NGC 3627 and NGC 3628 but does not appear to be interacting. NGC 3623’s kinematics an has barely been studied and observations provide a glimpse of its dynamics. The large-scale velocity reveals minor-axis rotation, in agreement with the presence of a bar. In addition, a quasi edge-on disk is present in the center, where the iso velocity contours flatten out abruptly.”

History of Observation:

Both M65 and M66 were discovered on the same night – March 1, 1780 – by Charles Messier, who described M65 as “Nebula discovered in Leo: It is very faint and contains no star.” Sir William Herschel would later observe M65 as well, describing it as “A very brilliant nebula extended in the meridian, about 12′ long. It has a bright nucleus, the light of which suddenly diminishes on its border, and two opposite very faint branches.”

However, it would be Lord Rosse who would be the first to see structure: “March 31, 1848. – A curious nebula with a bright nucleus; resolvable; a spiral or annular arrangement about it; no other portion of the nebula resolved. Observed April 1, 1848 and April 3, with the same results.”

Locating Messier 65:

Even though you might think by its apparent visual magnitude that M65 wouldn’t be visible in small binoculars, you’d be wrong. Surprisingly enough, thanks to its large size and high surface brightness, this particular galaxy is very easy to spot directly between Iota and Theta Leonis. In even 5X30 binoculars under good conditions you’ll easy see both it and M66 as two distinct gray ovals.

*Messier 65 location. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)*

A small telescope will begin to bring out structure in both of these bright and wonderful galaxies, but to get a hint at the “Trio” you’ll need at least 6″ in aperture and a good dark night. If you don’t spot them right away in binoculars, don’t be disappointed – this means you probably don’t have good sky conditions and try again on a more transparent night. The pair is well suited to modestly moonlit nights with larger telescopes.

Capture one of the Trio tonight! And here are the quick facts on this Messier Object:

Object Name: Messier 65
Alternative Designations: M65, NGC 3623, (a member of the) Leo Trio, Leo Triplet
Object Type: Type Sa Spiral Galaxy
Constellation: Leo
Right Ascension: 11 : 18.9 (h:m)
Declination: +13 : 05 (deg:m)
Distance: 35000 (kly)
Visual Brightness: 9.3 (mag)
Apparent Dimension: 8×1.5 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, M1 – The Crab Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

January 1, 2018January 1, 2018 by Tammy Plotner

Messier 64 – The Black Eye Galaxy

Image of the Black Eye Galaxy (Messier 64), taken with Hubble's Wide Field Planetary Camera 2 (WFPC2). Credit: NASA and The Hubble Heritage Team (AURA/STScI)

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at that “evil” customer known as Messier 64 – aka. the “Black Eye Galaxy”!

One of these objects is known as Messier 64, which is also known as the “Black Eye” or “Evil Eye Galaxy”. Located in the Coma Berenices constellation, roughly 24 million light-years from Earth, this spiral galaxy is famous for the dark band of absorbing dust that lies in front of the galaxy’s bright nucleus (relative to Earth). Messier 64 is well known among amateur astronomers because it is discernible with small telescopes.

Description:

Residing about 19 million light years from our home galaxy, the “Sleeping Beauty” extends across space covering an area nearly 40,000 light years across, spinning around at a speed of 300 kilometers per second. Toward its core is a counter-rotating disc approximate 4,000 light years wide and the friction between these two may very well be the contributing factor to the huge amounts of starburst activity and distinctive dark dust lane.

Infrared image taken by the Hubble Space Telescope, which penetrated the dust clouds swirling around the centers of the M64 galaxy. Credits: Torsten Boeker, Space Telescope Science Institute and NASA/ESA

Stars themselves appear to be forming in two waves, first evolving outside following the density gradient where abundant interstellar matter was waiting, and then evolving slowly. As the material from the mature stars began beig pushed back by their stellar winds, supernovae, and planetary nebulae, increased amounts of interstellar matter once again compressed, beginning the process of star formation again. This “second wave” may very well be represented by the dark, obscuring dust lane we see.

But, M64 isn’t without it share of turmoil. Its dual rotation may have started as a collision when two galaxies merged some billion years ago – or so theory would suggest. But did it? As Robert Braun and Rene Walterbos explained in their 1995 study:

“This galaxy is known to contain two nested, counter rotating, gas disks of a few 108 solar mass each, with the inner disk extending to approximately 1 kpc and the outer disk extending beyond. The stellar kinematics along the major axis, extending across the transition region between the two gas disks, show no hint of velocity reversal or increased velocity dispersion. The stars always rotate in the same sense as the inner gas disk, and thus it is the outer disk which ‘counterrotates’. The projected circular velocities inferred from the stellar kinematics and from the H I disks agree to within approximately 10 km/s, supporting other evidence that the stellar and gaseous disks are coplanar to approximately 7 deg. This upper limit is comparable to the mass of detected counter rotating gas. This low mass of counter rotating material, combined with the low-velocity dispersion in the stellar disk, implies that NGC 4826 cannot be the product of a retrograde merger of galaxies, unless they differed by at least an order of magnitude in mass. The velocities of the ionized gas along the major axis are in agreement with that of the stars for R less than 0.75 kpc. The subsequent transition toward apparent counter rotation of the ionized gas is spatially well resolved, extending over approximately 0.6 kpc in radius. The kinematics of this region are not symmetric with respect to the galaxy center. On the southeast side there is a significant region in which vproj (H II) much less than vcirc approximately 150 km/s, but sigma (H II) approximately 65 km/s. The kinematic asymmetries cannot be explained with any stationary dynamical model, even is gas inflow or warps were invoked. The gas in this transition region shows a diffuse spatial structure, strong (N II) and (S II) emission, as well as the high-velocity dispersion. These data present us with the conundrum of explaining a galaxy in which a stellar disk, and two counter rotating H I disks, at smaller and much larger radii, appear in equilibrium and nearly coplanar, yet in which the transition region between the gas disks is not in steady state.”

So is all what it really appears to be? Are new stars being born in the darkness? As A. Majeed (et al) indicated in their 1999 study:

“The Evil Eye galaxy (NGC 4826; M64) is distinguished by an asymmetrically placed, strongly absorbing dust lane across its prominent bulge. We obtained a long-slit spectrum of NGC 4826, with the slit across the galaxy’s nucleus, covering equal parts of the obscured and the unobscured portions of the bulge. By comparing the spectral energy distributions at corresponding positions on the bulge, symmetrically placed with respect to the nucleus, we were able to study the wavelength dependent effects of absorption, scattering, and emission by the dust, as well as the presence of ongoing star formation in the dust lane. We report the detection of strong extended red emission (ERE) from the dust lane within about 15 arcsec distance from the nucleus of NGC 4826. The ERE band extends from 5400 A to 9400 A, with a peak near 8800 A. The integrated ERE intensity is about 75 % of that of the estimated scattered light from the dust lane. The ERE shifts toward longer wavelengths and diminishes in intensity as a region of star formation, located beyond 15 arcsec distance, is approached. We interpret the ERE as originating in photoluminescence by nanometer-sized clusters, illuminated by the galaxy’s radiation field, in addition to the illumination by the star-forming complex within the dust lane. When examined within the context of ERE observations in the diffuse ISM of our Galaxy and in a variety of other dusty environments such as nebulae, we conclude that the ERE photon conversion efficiency in NGC 4826 is as high as found elsewhere, but that the size of the nanoparticles in NGC 4826 is about twice as large as those thought to exist in the diffuse ISM of our Galaxy.”

*Messier 64 (“Black Eye Galaxy”) imaged using amateur telescope. Credit: Jeff Johnson.*

But the debate is still on. As R.A. Walterbos (et al) expressed in their 1993 study:

“The close to coplanar orientation of the gas disks is one aspect which is in good agreement with what is expected on the basis of a merger model for the counter-rotating gas. The rotation direction of the inner gas disk with respect to the stars, however, is not. In addition, the existence of a well defined exponential disk probably implies that if a merger did occur it must have been between a gas-rich dwarf and a spiral, not between two equal mass spirals. The stellar spiral arms of NGC 4826 are trailing over part of the disk and leading in the outer disk. Recent numerical calculations by Byrd et al. for NGC 4622 suggest that long lasting leading arms could be formed by a close retrograde passage of a small companion. In this scenario, the outer counter-rotating gas disk in NGC 4826 might be the tidally stripped gas from the dwarf. However, in NGC 4826 the outer arms are leading, while it appears that in NGC 4622 the inner arms are leading. A realistic N-body/hydro simulation of a dwarf-spiral encounter is clearly needed. It may also be possible that the counter-rotating outer gas disk is due to gradual infall of gas from the halo, rather than from a discrete merger event.”

History of Observation:

M64 was discovered by Edward Pigott on March 23, 1779, just 12 days before Johann Elert Bode found it independently on April 4, 1779. Roughly a year later, Charles Messier independently rediscovered it on March 1, 1780 and cataloged it as M64. Said Pigot:

“.. on the 23rd of March [1779], I discovered a nebula in the constellation of Coma Berenices, hitherto, I presume, unnoticed; at least not mentioned in M. de la Lande’s Astronomy, nor in M. Messier’s ample Catalogue of nebulous Stars [of 1771]. I have observed it in an acromatic instrument, three feet long, and deduced its mean R.A. by comparing it to the following stars Mean R.A. of the nebula for April 20, 1779, of 191d 28′ 38″. Its light being exceedingly weak, I could not see it in the two-feet telescope of our quadrant, so was obliged to determine its declination likewise by the transit instrument. The determination, however, I believe, may be depended upon to two minutes: hence, the declination north is 22d 53″1/4. The diameter of this nebula I judged to be about two minutes of a degree.”

However, Pigott’s discovery got published only when read before the Royal Society in London on January 11, 1781, while Bode’s was published during 1779 and Messier’s in late summer, 1780. Pigott’s discovery was more or less ignored and recovered only by Bryn Jones in April 2002! (May the good Mr. Pigot know that he was remembered here and his reports placed first!!)

*Messier 64, the Black Eye Galaxy. Credit: Miodrag Sekulic*

So how did it get the name “Black Eye Galaxy”? We have Sir William Herschel to thank for that: “A very remarkable object, much elongated, about 12′ long, 4′ or 5′ broad, contains one lucid spot like a star with a small black arch under it, so that it gives one the idea of what is called a black eye, arising from fighting.” Of course, John Herschel perpetuated it when he wrote in his own notes:

“The dark semi-elliptic vacancy (indicated by an unshaded or bright portion in the figure,) which partially surrounds the condensed and bright nucleus of this nebula, is of course unnoticed by Messier. It was however seen by my Father, and shown by him to the late Sir Charles Blagden, who likened it to the appearance of a black eye, an odd, but not inapt comparison. The nucleus is somewhat elongated, and I have a strong suspicion that it may be a close double star, or extremely condensed double nebula.”

Locating Messier 64:

Locating M64 isn’t particularly easy. Begin by identifying bright orange Arcturus and the Coma Berenices star cluster (Melotte 111) about a hand span to the general west. As you relax and let your eyes dark adapt, you will see the three stars that comprise the constellation of Coma Berenices, but if you live under light polluted skies, you may need binoculars to find its faint stars. Once you have confirmed Alpha Comae, star hop approximately 4 degrees north/northwest to 35 Comae. You will find M64 around a degree to the northeast of star 35.

While Messier 64 is binocular possible, it will require very dark skies for average binoculars and will only show as a very small, oval contrast change. However, in telescopes as small as 102mm, its distinctive markings can be seen on dark nights with good clarity. Don’t fight over it… There’s plenty of dark dustlane in this Sleeping Beauty to go around!

*The location of Messier 64 in the Coma Berenices constellation. Credit: IAU/Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)*

And here are the quick facts on this Messier Object to help you get started:

Object Name: Messier 64
Alternative Designations: M64, NGC 4826, The Black Eye Galaxy, Sleeping Beauty Galaxy, Evil Eye Galaxy
Object Type: Type Sb Spiral Galaxy
Constellation: Coma Berenices
Right Ascension: 12 : 56.7 (h:m)
Declination: +21 : 41 (deg:m)
Distance: 19000 (kly)
Visual Brightness: 8.5 (mag)
Apparent Dimension: 9.3×5.4 (arc min)

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

December 11, 2017December 11, 2017 by Tammy Plotner

Messier 63 – the Sunflower Galaxy

The Sunflower Galaxy, a spiral galaxy located in the northern constellation Canes Venatici, as imaged by the NASA/ESA Hubble Space Telescope. Credits: ESA/Hubble & NASA

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the “Sunflower Galaxy”, otherwise known as Messier 63.

One of these objects is the spiral galaxy known as Messier 63 – aka. the Sunflower Galaxy. Located in the Canes Venatici constellation, this galaxy is located roughly 37 million light-years from Earth and has an active nucleus. Messier 63 is part of the M51 Group, a group of galaxies that also includes Messier 51 (the ‘Whirlpool Galaxy’), and can be easily spotted using binoculars and small telescopes.

Description:

Messier 63 is what is known as a a flocculent spiral galaxy, consisting of a central disc surrounded by many short spiral arm segments – one not connected by a central bar structure. Drifting along in space some 37,000 light years from our own galaxy, we known it interacts gravitationally with M51 (the Whirlpool Galaxy) and we also know that its outer regions are rotating so quickly that if it weren’t for dark matter – it would rip itself apart.

Infrared image of the Sunflower Galaxy (Messier 63) taken by the Spitzer Space Telescope. Credit: NASA/JPL-Caltech/SINGS Team

As Michele D. Thornley and Lee G. Mundy, of the Maryland University Department of Astronomy, indicated in a 1997 study:

“The morphology and inematics described by VLA observations of H I emission and FCRAO and Berkeley-Illinois-Maryland Association (BIMA) Array observations of CO emission provide evidence for the presence of low-amplitude density waves in NGC 5055. The distribution of CO and H I emission suggests enhanced gas surface densities along the NIR spiral arms, and structures similar to the giant molecular associations found in the grand design spirals M51 and M100 are detected. An analysis of H I and H? velocity fields shows the kinematic signature of streaming motions similar in magnitude to those of M100 in both tracers. The lesser degree of organization along the spiral arms of NGC 5055 may be due to the lower overall gas surface density, which in the arms of NGC 5055 is a factor of 2 lower than in M100 and a factor of 6 lower than in M51; an analysis of gravitational instability shows the gas in the arms is only marginally unstable and the interarm gas is marginally stable. The limited extent of the spiral arm pattern is consistent with an isolated density wave with a relatively high pattern speed.”

There very well could be a massive object hidden within. As Sebastien Blais-Ouellette of the Universite de Montreal said in a 1998 study:

“In a global kinematical study of NGC 5055 using high resolution Fabry-Perot, intriguing spectral line profiles have been observed in the center of the galaxy. These profiles seem to indicate a rapidly rotating disk with a radius near 365 pc and tilted 50 deg with respect to the major axis of the galaxy. In the hypothesis of a massive dark object, a naive keplerian estimate gives a mass around 10^7.2 to 10^7.5 M.”

*Infrared image of the M63 galaxy made by Médéric Boquien, using data retrieved on the SINGS project public archives of the Spitzer Space Telescope. Credit: NASA/JPL-Caltech*

But that’s not all they’ve found either… How about a lopsided, chemically unbalanced nucleus! As V.L. Afanasiev (et al) pointed out in their 2002 study:

“We have found a resolved chemically distinct core in NGC 5055, with the magnesium-enhanced region shifted by 2″.5 (100 pc) to the south-west from a photometric center, toward a kinematically identified circumnuclear stellar disk. Mean ages of stellar populations in the true nucleus, defined as the photometric center, and in the magnesium-enhanced substructure are coincident and equal to 3-4 Gyr being younger by several Gyr with respect to the bulge stellar population.”

Yep. It might be beautiful, but it’s warped. As G. Battaglia of the Kapteyn Astronomical Institute indicated in a 2005 study:

“NGC 5055 shows remarkable overall regularity and symmetry. A mild lopsidedness is noticeable, however, both in the distribution and kinematics of the gas. The tilted ring analysis of the velocity field led us to adopt different values for the kinematical centre and for the systemic velocity for the inner and the outer parts of the system. This has produced a remarkable result: the kinematical and geometrical asymmetries disappear, both at the same time. These results point at two different dynamical regimes: an inner region dominated by the stellar disk and an outer one, dominated by a dark matter halo offset with respect to the disk.”

*Sunflower Galaxy (Messier 63). Credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona*

History of Observation:

Messier Object 63 was the very first discovery by Charles Messier’s friend and assistant Pierre Mechain, who turned it up on June 14, 1779. While Mechain himself did not write the notes, Messier did:

“Nebula discovered by M. Mechain in Canes Venatici. M. Messier searched for it; it is faint, it has nearly the same light as the nebula reported under no. 59: it contains no star, and the slightest illumination of the micrometer wires makes it disappear: it is close to a star of 8th magnitude, which precedes the nebula on the hour wire. M. Messier has reported its position on the Chart of the path of the Comet of 1779.”

Messier 63 would go on to be observed and resolved by Sir William Herschel and cataloged by his son John. It would be descriptively narrated by Admiral Symth and exclaimed over by many astronomers – one of the best of which was Lord Rosse: “Spiral? Darkness south flowing nucleus.” Of all the descriptions, perhaps the best belongs to Curtis, who first photographed it with the Crossley Reflector at Lick Observatory: “Has an almost stellar nucleus. The whorls are narrow, very compactly arranged, and show numerous almost stellar condensations.”

Locating Messier 63:

The beautiful Sunflower Galaxy is among one of the easiest of the Messier objects to find. It’s located almost precisely between Cor Caroli (Alpha Canes Venetici) and Eta Ursa Majoris. With the slightest of optical aid, stars 19, 20 and 23 CnV will show easily in finderscope or binoculars and M63 will be positioned right around two degrees away towards Eta UM.

*The location of Messier 63 in the Canes Venatici constellation. Credit: IAU/Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)*

While this spiral galaxy has a nice overall brightness, it’s going to be very faint for binoculars, only showing as the tiniest contrast change in smaller models. However, even a modest telescope will easily see a faint oval shape with a concentrated nucleus. The more aperture you apply, the more details you will see. As size approaches 8″ and larger, expect to see spiral structure!

Power up… And look for the spiral in the Sunflower!

Object Name: Messier 63
Alternative Designations: M63, NGC 5055, Sunflower Galaxy
Object Type: Type Sb Spiral Galaxy
Constellation: Canes Venatici
Right Ascension: 13 : 15.8 (h:m)
Declination: +42 : 02 (deg:m)
Distance: 37000 (kly)
Visual Brightness: 8.6 (mag)
Apparent Dimension: 10×6 (arc min)

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

December 8, 2017January 30, 2018 by Tammy Plotner

The Dorado Constellation

The location of the southern Dorado constellation. Credit and Copyright: Torsten Bronger

Welcome to another edition of Constellation Friday! Today, in honor of the late and great Tammy Plotner, we take a look at that fishiest of asterisms – the Dorado constellation. Enjoy!

In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age.

Since that time, many additional constellations have been discovered, such as Dorado. This southern constellation, which was discovered in the 16th century by Dutch navigators, is now one of the 88 constellations recognized by the International Astronomical Union (IAU). It is bordered by the constellations of Caelum, Horologium, Hydrus, Mensa, Pictor, Reticulum, and Volans.

Name and Meaning:

Because of its southerly position, Dorado was unknown to the ancient Greeks and Romans so no classical mythological connection exists. However, there are some very nice tales and history associated with this constellation. The name Dorado is Spanish for mahi-mahi, or the dolphin-fish. The mahi-mahi has a opalescent skin that turns blue and gold as the fish dies.

Image of the night sky taken at the European Southern Observatory’s Very Large Telescope in Chile. The Large and Small Magellanic Clouds are visible in the night sky. Credit: ESO, Y. Beletsky

This may very well be the reason Dorado is sometimes called the goldfish is certain stories and legends. Because the early Dutch explorers observed the mahi-mahi chasing swordfish, Dorado was added to their new sky charts following the constellation of the flying fish, Volans. Some very old star atlases refer to Dorado as Xiphias, another form of swordfish, but clearly its “fishy” nature stands!

History of Observation:

Dorado was one of twelve constellations named by Dutch astronomer Petrus Plancius, based on the observations of Dutch sailors that explored the southern hemisphere during the 16th century. It first appeared on a celestial globe published circa 1597-8 in Amsterdam. Dorado was taken a bit more seriously when it was included by Johann Bayer in 1603 in his star atlas, Uranometria, where it appeared under its current name.

It has endured to become one of the 88 modern constellations adopted and approved by the International Astronomical Union.

Notable Objects:

Covering 179 square degrees of sky, it consists of three main stars and contains 14 Bayer/Flamsteed designated stellar members. Dorado has several bright stars and contains no Messier objects. The brightest star in the constellation is Alpha Doradus, a binary star that is approximately 169 light years distant. This binary system is one of the brightest known, and is composed of a blue-white giant (classification A0III) and a blue-white subgiant (B9IV).

*The Tarantula Nebula (NGC 2070) located in the southern Dorado constelaltion. Credit: ESO*

Beta Doradus, the second brightest star in the constellation, is a Cepheid variable star located approximately 1,050 light years from Earth. Its spectral type varies from white (F-type) to yellow (G-type), like our Sun. Gamma Doradus is another variable, which serves as a prototype for stars known as Gamma Doradus variables, and is approximately 66.2 light years distant.

Another interesting character is HE 0437-5439, an unbound hypervelocity star in Dorado discovered in 2005. This star appears to be receding at the speed of 723 km/s (449 mi/s), and is therefore no longer gravitationally bound to the Milky Way. It is approximately 200,000 light years distant and is a main sequence star belonging to the spectral type BV (a white-blue subdwarf).

Most notable is the Large Magellanic Cloud (LMC), an irregular galaxy located in the constellations Dorado and Mensa. This satellite galaxy to the Milky Way is roughly 1/100 times as massive as our galaxy, with an estimated ten billion times the mass of the Sun. Located about 157,000 light years away, the LMC is home to several impressive objects – like the Tarantula Nebula and the Ghost Head Nebula.

There are no meteor showers associated with the constellation.

The Ghost Head Nebula (NGC 2080), . Credit: ESA/NASA/Mohammad Heydari-Malayeri

Finding Dorado:

The South Ecliptic Pole lies within Dorado and it is bordered by the constellations of Caelum, Horologium, Reticulum, Hydrus, Mensa, Volans and Pictor. It is visible at latitudes between +20° and -90° and is best seen at culmination during the month of January. Let’s begin our explorations with binoculars and Alpha Doradus – the “a” symbol on our map. One of the reasons this star shines so brightly is because it’s not one – but two.

Don’t get your telescope out just yet, because Alpha is separated by only only a couple tenths of a second of arc and both members are about a magnitude apart. Located about 175 light years away from our solar system, this tight pair averages a distance between each other that’s equal to about the same distance as Saturn from our Sun. That’s not particularly unusual for a binary star, but what is unusual is the primary star. Alpha Dor A’s spectrum is “peculiar” – very rich in silicon. It seems to be concentrated in a stellar magnetic spot!

Let’s have a look at Cephid variable star Beta Doradus – the “B” symbol on our map. Beta is an evolved super giant star and every 9.942 days it reaches a maximum brightness of magnitude 3.46 then drops to magnitude 4.08. While these types of changes are so slight they would be difficult to follow with just the eye, that doesn’t mean what happens isn’t important. By studying Cephids we understand “period-luminosity” relation. The pulsation period of a Cepheid gives us absolute brightness, and comparing it with apparent brightness gives us distance. That way, when we find a Cepheid variable star in another galaxy, we can tell just how far away that galaxy is!

Now, let’s go from one end of the constellation to the other with binoculars as we start with Delta Doradus – the “8” shape on our map. If you were on the Moon, this particular star would be the south “pole star” – just like Polaris is to the north on Earth! Sweep along the body of the fish and end at Gamma Doradus – the “Y” shape on our map. Guess what? Another variable star! But this one isn’t a Cepheid. Gamma Doradus variables are variable stars which display variations in luminosity due to non-radial pulsations of their surface.

The stars are typically young, early F or late A type main sequence stars, and typical brightness fluctuations are 0.1 magnitudes with periods on the order of one day. This is a relatively new class of variable stars, having been first characterised in the second half of the 1990s, and details on the underlying physical cause of the variations remains under investigation. We call these mysterious strangers Oscillating Blue Stragglers.

Don’t put away your binoculars yet. We have to look at R Doradus! Here we have a red giant Mira variable star that’s about 200 to 225 light years away from Earth. The visible magnitude of R Doradus varies between 4.8 and 6.6, which makes the variable changes easy to follow with binoculars, but when viewed in the infrared it is one of the brightest stars in the sky. However, this isn’t what the most interesting part is.

With the exception of our own Sun, R Doradus is currently believed to be the star with the largest apparent size as viewed from Earth. The stellar diameter of R Doradus could be as much as 585 million kilometers. That’s upwards to 400 times larger than Sol – yet it has about the same mass! If placed at the center of the Solar System, the orbit of Mars would be entirely contained within the star. Too cool…

Dorado contains a huge amount of deep sky objects very well suited for binoculars, small and large telescopes. So many, in fact, our small star chart would be so cluttered that it would be impossible to read designations. One of the most notable of all is the Large Magellanic Cloud, one of our Milky Way Galaxy’s neighbors and members of our local galaxy group. In itself, it is an irregular dwarf galaxy, distorted by tidal interaction with the Milky Way and may have once been barred spiral galaxies.

The Magellanic Clouds’ radial velocity and proper velocity were recently accurately measured by a team from the Harvard-Smithsonian Center for Astrophysics to produce a 3-D velocity measurement that clocked their passage through the Milky Way galaxy in excess of 480km/s (300 miles per second) using input from Hubble Telescope. This unusually high velocity seems to imply that they are in fact not bound to the Milky Way, and many of the presumed effects of the Magellanic Clouds have to be revised. Be sure to explore the LMC for its own host of nebula and star forming regions. It was host to a supernova (SN 1987A), the brightest observed in over three centuries!

For the telescope, there are many objects in Dorado that you don’t want to miss. (This article would be 10 pages long if I listed them all, so let’s just highlight a few.) For galaxy group fans, why not choose NGC 1566 (RA 04h 20m 00s Dec -56 56.3′) NGC 1566 is a spiral galaxy that dominates the Dorado Group and it is also a Seyfert galaxy as well. At the center of the cluster, look for interacting galaxies NGC 1549 and NGC 1553.

These two bright members are lenticular galaxy NGC 1553 (RA 04h 16m 10.5s Dec -55 46′ 49″), and elliptical galaxy NGC 1549 (RA 04h 15m 45.1s Dec -55 35′ 32″). Their interaction appears to be in the early stage and can be seen in optical wavelengths by faint but distinct irregular shells of emission and a curious jet on the northwest side. Chandra X-ray imaging of NGC 1553 show diffuse hot gas making up 70% of the emissions, dotted with many point-like sources (low-mass X-ray binaries) making up the rest.

Similar to Messier 60, these bright spots are binary star systems of black holes and neutron stars most of which are located in globular clusters and reflect this old galaxy’s very active past. In these systems, material pulled off a regular star is heated and gives off X-rays as it falls toward the accompanying black hole or neutron star.

*The location of the southern Constellation Dorado. Credit: IAU/Sky&Telescope magazine*

Turn your telescope towards NGC 2164 (RA 05h 58m 53s Dec -68 30.9′). Here we are resolving an open star cluster / globular cluster that’s in another galaxy, folks! Also nearby you’ll find faint open cluster NGC 2172 (RA 5 : 59.9 Dec -68 : 38) and galactic star cluster NGC 2159 (05 57.8, -68 38). What a treat to study in another galaxy!

Would you like to study another complex? Then let’s take a look at NGC 2032 (RA 05h 35m 21s Dec -67 34.1′). Better known as the “Seagull Nebula” this complex that contains four separate NGC designations: NGC 2029, NGC 2032, NGC 2035 and NGC 2040. Spanning across an open star cluster, there are many nebula types here including emission nebula, reflection nebula and HII regions. It is also bissected by a dark nebula, too!

Of course, no telescope trip through Dorado would be complete without stopping by NGC 2070 (RA 05h 38m 37s Dec -69 05.7′) – the “Tarantula Nebula”. Located about 180,000 light years from our solar system and first recorded by Nicolas Louis de Lacaille in 1751, this huge HII region is an extremely luminous object. Its luminosity is so bright that if it were as close to Earth as the Orion Nebula, the Tarantula Nebula would cast shadows. In fact, it is the most active starburst region known in our Local Group of galaxies! At its core lies the extremely compact cluster of stars that provides the energy to make the nebula visible. And we’re glad it does!

We have written many interesting articles about the constellation here at Universe Today. Here is What Are The Constellations?, What Is The Zodiac?, and Zodiac Signs And Their Dates.

Be sure to check out The Messier Catalog while you’re at it!

For more information, check out the IAUs list of Constellations, and the Students for the Exploration and Development of Space page on Canes Venatici and Constellation Families.

Sources:

December 4, 2017December 4, 2017 by Tammy Plotner

Messier 62 – the NGC 6266 Globular Cluster

Messier 62, shown in proximity to Messier 19 and Antares. Credit: Wikisky

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the globular cluster known as Messier 62.

One of these objects is the globular cluster known as Messier 62, which spans about 100 light-years in diameter and is approximately 22,200 light years from Earth. Located in the southern constellation of Ophiuchus, this cluster is easy to find because of its proximity to Antares – the brightest star in Scorpius constellation – and is easily viewed suing binoculars and small telescopes.

Description:

Positioned about 22,500 light years away from Earth, this glorious gravitationally bound ball of stars could span as much as 100 light years of space. Captured within its confines are 89 known variable stars – most of them RR Lyrae types. M62 has a very dense core… One which may have experienced core collapse during its long history. An ordinary globular cluster? Not hardly. It’s one that holds some optical surprises.

*The globular cluster Messier 62 in the constellation Ophiuchus. Credit: Wikipedia Commons/Hewholooks*

As G. Cocozza (et al) indicated in their 2008 study:

“We report on the optical identification of the companion to the eclipsing millisecond pulsar PSR J1701-3006B in the globular cluster NGC 6266. A relatively bright star with an anomalous red color and an optical variability (~0.2 mag) that nicely correlates with the orbital period of the pulsar (~0.144 days) has been found nearly coincident with the pulsar nominal position. This star is also found to lie within the error box position of an X-ray source detected by Chandra observations, thus supporting the hypothesis that some interaction is occurring between the pulsar wind and the gas streaming off the companion. Although the shape of the optical light curve is suggestive of a tidally deformed star which has nearly completely filled its Roche lobe, the luminosity (~1.9 Lsolar) and the surface temperature (~6000 K) of the star, deduced from the observed magnitude and colors, would imply a stellar radius significantly larger than the Roche lobe radius.”

Is it possible that this is the smoking gun for intermediate mass black holes in globular clusters? Julio Chaname seems to think so. As he explained in his 2009 study:

“The existence of intermediate-mass black holes [IMBHs] in star clusters has been predicted by a variety of theoretical arguments and, more recently, by several large, realistic sets of collisional N-body simulations. Establishing their presence or absence at the centers of globular clusters would profoundly impact our understanding of problems ranging from the formation and long-term dynamical evolution of stellar systems, to the nature of the seeds and the growth mechanisms of the supermassive black holes {BHs} that inhabit the centers of most large, luminous galaxies. Observationally, the unambiguous signature of a massive central BH would be the discovery of central, unresolved X-ray or radio emission that is not consistent with more common stellar-mass accreting objects or pulsars. Yet, due to the largely uncertain details of accretion modeling, a precise mass determination of a central BH must necessarily come from stellar dynamics. This goal has not been achieved to date at the centers of Galactic globular clusters because of lack of adequate data as well as the use of too simplified methods of analysis. This situation can be overcome today through the combination of HST proper-motion measurements and state-of-the-art dynamical models specifically designed to take full advantage of this type of dataset. In this project, we will use two HST orbits to obtain another epoch of observations of NGC 6266. This cluster has photometric and structural properties that are consistent with current theoretical expectations for a cluster harboring an IMBH. Even more importantly, it is the only Galactic globular cluster for which there exists a detection of radio emission coincident with the cluster’s core, and with a flux density that appears to rule out a stellar or binary origin. The goal of our project is to obtain proper motion measurements to either confirm an IMBH in this cluster and measure its mass, or to set limits to its mass and existence.”

*The Messier 62 globular cluster, as imaged by the Hubble Space Telescope. Credit: NASA, ESA*

History of Observation:

While Charles Messier first discovered this globular cluster on June 7, 1771 – he didn’t accurately record its position until June 4, 1779.

“”Very beautiful nebula, discovered in Scorpio, it resembles a little Comet, the center is brilliant and surrounded by a faint glow. Its position determined, by comparing it with the star Tau of Scorpius. M. Messier had already seen this nebula on June 7, 1771, without having determined the position where it is close to. Seen again on March 22, 1781.”

Sir William Herschel would resolve it two years after Messier cataloged it, but it was Admiral Smyth who gave it a little more historic significance when he writes in his notes:

“A fine large resolvable nebula, at the root of the creature’s [Scorpion’s] tail, and in the preceding part of the Galaxy [Milky Way band]. It is an aggregated mass of small stars running up to a blaze in the centre, which renders the differentiating comparatively easy and satisfactory; and in this instance it was referred to its neighbor, 26 Ophiuchi, which is 5deg distant to the north: and it lies only about 7deg from Antares, on the south-east. This was registered in 1779, and Messier described it as “a very pretty nebula, resembling a little comet, the centre bright, and surrounded by a faint light.” Sir William Herschel, who first resolved it, pronounced it a miniature of Messier’s No. 3, and adds, “By the 20-foot telescope, which at the time of these observations was of the Newtonian construction, the profundity of this cluster is of the 734th order.” To my annoyance, it was started as a comet a few years ago, by a gentleman who ought to have known better.”

Locating Messier 62:

M62 is easily located about 5 degrees (3 finger widths) southeast of Antares – but because it is small, it can easily be overlooked in binoculars. Take your time, because it is only just a little more than an average binocular field away from an easy marker star and bright enough to be seen even with smaller instruments under not so good skies.

*The locations of Messier 62 in the Ophiuchus constellation. Credit: IAU/Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)*

In the finderscope of a telescope, begin with Antares in the center and shift southwest. At 5X magnification, it will show as a faint haze. In a small telescope, you may get some resolution – but expect this globular cluster to appear more comet-like. Larger telescopes can expect a wonderful explosion of stars!

Enjoy your observations! And as always, here are the quick facts on this Messier Object to help you get started:

Object Name: Messier 62
Alternative Designations: M62, NGC 6266
Object Type: Class IV Globular Cluster
Constellation: Ophiuchus
Right Ascension: 17 : 01.2 (h:m)
Declination: -30 : 07 (deg:m)
Distance: 22.5 (kly)
Visual Brightness: 6.5 (mag)
Apparent Dimension: 15.0 (arc min)

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

November 27, 2017December 4, 2017 by Tammy Plotner

Messier 61- the NGC 4303 Barred Spiral Galaxy

The Messier 61 galaxy, as imaged by the Hubble Space Telescope. Credits: ESA/Hubble & NASA/G. Chapdelaine, L. Limatola and R. Gendler

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the barred spiral galaxy known as Messier 61.

One of these objects is the intermediate barred spiral galaxy known as Messier 61. As one of the larger galaxies located in the Virgo Cluster, this galaxy is roughly 52.5 million light years from Earth and contains some spectacular supernovae. It also has an Active Galactic Nucleus (AGN), meaning it has a Supermassive Black Hole (SMBH) at its center, and shows evidence of considerable star formation.

What You Are Looking At:

Spanning about 100,000 light years across and about the same size as our own Milky Way Galaxy, this grand old spiral is one of the largest in the Virgo Cluster… and one of the most active in terms of starbursts and supernovae. According to Luis Colina (et al) indicated in a 1997 study:

“A high-resolution Hubble Space Telescope WFPC2 F218W UV image of the barred spiral NGC 4303 (classified as a LINER-type active galactic nucleus [AGN]) reveals for the first time the existence of a nuclear spiral structure of massive star-forming regions all the way down to the UV-bright unresolved core of an active galaxy. The spiral structure, as traced by the UV-bright star-forming regions, has an outer radius of 225 pc and widens as the distance from the core increases. The UV luminosity of NGC 4303 is dominated by the massive star-forming regions, and the unresolved LINER-type core contributes only 16% of the integrated UV luminosity. The nature of the UV-bright LINER-type core—stellar cluster or pure AGN—is still unknown.”

*The Virgo Cluster Galaxies. Credit & Copyright: Rogelio Bernal Andreo*

Another fascinating aspect is Colina’s team has also identified a Super Star Cluster (SSC) withing Messier 61 as well. As Colina indicated in a 2002 study:

“These new HST/STIS results unambiguously show the presence of a compact SSC in the nucleus of a low-luminosity AGN, which is also its dominant ionizing source. We hypothesize that at least some LLAGNs in spirals could be understood as the result of the combined ionizing radiation emitted by an evolving SSC (i.e., determined by the mass and age) and a black hole accreting with low radiative efficiency (i.e., radiating at low sub-Eddington luminosities) coexisting in the inner few parsecs region. Complementary multifrequency studies give the first hints of the very complex structure of the central 10 pc of NGC 4303, where a young SSC apparently coexists with a low-efficiency accreting black hole and with an intermediate/old compact star cluster and where, in addition, an evolved starburst could also be present. If structures such as those detected in NGC 4303 are common in the nuclei of spirals, the modeling of the different stellar components and their contribution to the dynamical mass has to be established accurately before deriving any firm conclusion about the mass of central black holes of few to several million solar masses.”

Of course, studies don’t just stop there. As D. Tschoke (et al) indicated in a 2000 study:

“The late-type galaxy NGC 4303 (M61) is one of the most intensively studied barred galaxies in the Virgo Cluster. Its prominent enhanced star formation throughout large areas of the disk can be nicely studied due to its low inclination of about 27 degr. We present observations of NGC 4303 with the ROSAT PSPC and HRI in the soft X-ray (0.1-2.4 keV). The bulk of the X-ray emission is located at the nuclear region. It contributes more than 80% to the total observed soft X-ray flux. The extension of the central X-ray source and the L_X/L_Halpha ratio point to a low luminous AGN (LINER) with a circumnuclear star-forming region. Several separate disk sources can be distinguished with the HRI, coinciding spatially with some of the most luminous HII regions outside the nucleus of NGC 4303. The total star formation rate amounts to 1-2 Msun/yr. The X-ray structure follows the distribution of star formation with enhancement at the bar-typical patterns. The best spectral fit consists of a power-law component (AGN and HMXBs) and a thermal plasma component of hot gas from supernova remnants and superbubbles. The total 0.1-2.4 keV luminosity of NGC 4303 amounts to 5×10^40 erg/s, consistent with comparable galaxies, like e.g. NGC 4569.”

*Hubble picture is the sharpest ever image of the core of spiral galaxy Messier 61. Taken using the High Resolution Channel of Hubble’s Advanced Camera for Surveys. Credit: ESA/NASA/HST*

When it comes right down to it, it’s all about that star-forming ring. Said Eva Schinnerer (eta al) in a 2002 study:

“The UV continuum traces a complete ring that is heavily extincted north of the nucleus. Such a ring forms in hydrodynamic models of double bars, but the models cannot account for the UV emission observed on the leading side of the inner bar. Comparison with other starburst ring galaxies where the molecular gas emission and the star-forming clusters form a ring or tightly wound spiral structure suggests that the starburst ring in NGC 4303 is in an early stage of formation.”

How will today’s technologies continue to study the magnificent M61? Just take a look at what MOS can do! The very efficient multi-object-slit observing technique with the multi-mode instrument FORS1 has been demonstrated on the Virgo cluster galaxy NGC 4303 . Nineteen moveable slits at the instrument focal plane are positioned so that the faint light from several H II regions in this galaxy can pass into the spectrograph, while the much stronger “background” light (from the nearby areas in the galaxy and, to a large extent, from the Earth”s upper atmosphere) is blocked by the mask.

History of Observation:

M61 was discovered by Barnabus Oriani on May 5, 1779 when following the comet of that year. Said he, “Very pale and looking exactly like the comet.” As for our hero, Messier, he had also seen it on the same night – but thought it was the comet! Because Charles Messier was a good astronomer, he returned nightly to observe movement and it only took him a few days to realize his mistake and to admit it in his own notes:

“May 11, 1779. 61. 12h 10m 44s (182d 41′ 05″) +5d 42′ 05″ – Nebula, very faint & difficult to perceive. M. Messier mistook this nebula for the Comet of 1779, on the 5th, 6th and 11th of May; on the 11th he recognized that this was not the Comet, but a nebula which was located on its path and in the same point of the sky.”

*Supernova SN2008in in the spiral galaxy Messier 61. Credit: Hewholooks/ Wikipedia Commons*

Sir William and Sir John Herschel would also later return to M61 to assign it their own catalog numbers, both resolving certain portions of this wonderful galaxy – but neither truly beginning to understand what they were seeing. That took Admiral Smyth, who recorded in his notes:

“A large pale-white nebula, between the Virgo’s shoulders. This is a well defined object, but so feeble as to excite surprise that Messier detected it with his 3 1/2 foot telescope in 1779. Under the best action of my instrument it blazes towards the middle; but in H. [John Herschel]’s reflector it is faintly seen to be bicentral [an illusion caused by the bar], the nuclei 90″ apart, and lying sp [south preceding, SW] and nf [north following, NE]. It is preceded by four telescopic stars, and followed by another. Differentiated with the following object [17 Virginis], from which it bears about south by west, and is within a degree’s distance. This object is an outlier of a vast mass of discrete but neighboring nebulae, the spherical forms of which are indicative of compression.”

Locating Messier 61:

Locating Messier 61 is the Virgo Galaxy fields is relatively easily because it is so large and bright compared to any others in the area. Begin your hunt by identifying Beta and Delta Virginis. Between this pair you will see finderscope or binocular visible stars 17 and 16 Virginis. You destination is between this pair of stars. While M61 is binocular possible, it would require astronomical binoculars of approximately 80mm aperture and dark skies – although with excellent sky conditions the nucleus can be glimpsed with apertures as small as 60mm.

*This star chart for M61 represents the view from mid-northern latitudes for the given month and time. Credits: NASA/Stellarium*

In a small aperture telescope, M61 will appear as a very faint oval with a bright central region. As size increases, so do details and resolution. At 6-8″ in size, the nucleus becomes very clear and beginnings of spiral arms start to resolve. In the 10-12″ range, spiral structure becomes clear and some mottling texture becomes clear.

Enjoy your observations!

And here are the quick facts on Messier 61 to help you get started:

Object Name: Messier 61
Alternative Designations: M61, NGC 4303
Object Type: Type SABbc Spiral Galaxy
Constellation: Virgo
Right Ascension: 12 : 21.9 (h:m)
Declination: +04 : 28 (deg:m)
Distance: 60000 (kly)
Visual Brightness: 9.7 (mag)
Apparent Dimension: 6×5.5 (arc min)

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

November 20, 2017November 27, 2017 by Tammy Plotner

Messier 60 – the NGC 4649 Galaxy

The Messier 60 Elliptical Galaxy. Credits: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the elliptical galaxy known as Messier 60.

One of the notable objects in this catalog is Messier 60, an elliptical galaxy located approximately 55 million light-years away in the Virgo constellation. Measuring some 60,000 light years across, this galaxy is only about half as large as the Milky Way. However, it still manages to pack in an estimated 400 billion stars which, depending on which estimates you go by, is between four times and the same amount as our own.

What You Are Looking At:

Located about 60 million light years away and spanning about 120 million light years of space, M60 is the third brightest elliptical in the Virgo group and and is the dominant member of a subcluster of four galaxies, which is the closest-known isolated compact group of galaxies. In larger telescopes, you’ll see another nearby galaxy – NGC 4647 – which might first be taken for a interactor, but may very well lay at a different distance since there is no tidal evidence so far found.

*Messier 60. Credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona*

As L.M. Young (et al.) explained in their 2006 study:

“We present matched-resolution maps of H I and CO emission in the Virgo Cluster spiral NGC 4647. The galaxy shows a mild kinematic disturbance in which one side of the rotation curve flattens but the other side continues to rise. This kinematic asymmetry is coupled with a dramatic asymmetry in the molecular gas distribution but not in the atomic gas. An analysis of the gas column densities and the interstellar pressure suggests that the H2/H I surface density ratio on the east side of the galaxy is 3 times higher than expected from the hydrostatic pressure contributed by the mass of the stellar disk. We discuss the probable effects of ram pressure, gravitational interactions, and asymmetric potentials on the interstellar medium and suggest it is likely that a m = 1 perturbation in the gravitational potential could be responsible for all of the galaxy’s features. Kinematic disturbances of the type seen here are common, but the curious thing about NGC 4647 is that the molecular distribution appears more disturbed than the H I distribution. Thus, it is the combination of the two gas phases that provides such interesting insight into the galaxy’s history and into models of the interstellar medium.”

Although a search for young optical pulsars turned up negative after a recent supernova event, astronomer’s did discover something rather exciting… a supermassive black hole! As Philip J. Humphrey (et al) indicated in their 2008 study:

“We present a Chandra study of the hot ISM in the giant elliptical galaxy NGC4649. In common with other group-centred ellipticals, its temperature profile rises with radius in the outer parts of the galaxy. Under the assumption of hydrostatic equilibrium, we demonstrate that the central temperature spike arises due to the gravitational influence of a quiescent central super-massive black hole. This is the first direct measurement of MBH based on studies of hydrostatic X-ray emitting gas, which are sensitive to the most massive black holes, and is a crucial validation of both mass-determination techniques. This agreement clearly demonstrates the gas must be close to hydrostatic, even in the very centre of the galaxy, which is consistent with the lack of morphological disturbances in the X-ray image. NGC4649 is now one of only a handful of galaxies for which MBH has been measured by more than one method.”

History of Observation:

Both M59 and neighboring M60 were discovered on April 11, 1779 by Johann Gottfried Koehler who wrote: “Two very small nebulae, hardly visible in a 3-foot telescope: The one above the other.” It was independently found one day later by Barnabus Oriani, who missed M59, and four days later, on April 15, 1779, by Charles Messier, who also found nearby M58. In his notes Messier writes:

“Nebula in Virgo, a little more distinct than the two preceding [M58 and M59], on the same parallel as Epsilon [Virginis], which has served for its [position] determination. M. Messier reported it on the Chart of the Comet of 1779. He discovered these three nebulae while observing this Comet which passed very close to them. The latter passed so near on April 13 and 14 that the one and the other were both in the same field of the refractor, and he could not see it; it was not until the 15th, while looking for the Comet, that he perceived the nebula. These three nebulae don’t appear to contain any star.”

William Herschel would later perceive it as a double nebula and so would son John, calling it “A very fine and curious object.” However, it was Admiral Smyth who must have finally had a clear viewing night a took a look at what was all around!

“The hypothesis of Sir John Herschel, upon double nebulae, is new and attracting. They may be stellar systems each revolving round the other: each a universe, according to ancient notions. But as these revolutionary principles of those vast and distant firmamental clusters connot for ages yet be established, the mind lingers in admiration, rather than comprehension of such mysterious collocations. Meantime our clear duty is, so industriously to collect facts, that much of what is now unintelligible, may become plain to our successors, and a portion of the grand mechanism now beyond our conception, revealed. ‘How much,’ exclaims Sir John Herschel, ‘how much is escaping us! How unworthy is it in them who call themselves philosophers, to let these great phenomena of nature, these slow but majestic manifestations of power and the glory of God, glide unnoticed, and drop out of memory beyond the reach of recovery, because we will not take the pains to note them in their unobstrusive and furtive passage, because we see them in their every-day dress, and mark no sudden change, and conclude that all is dead, because we will not look for signs of life; and that all is uninteresting, because we are not impressed and dazzled.’ ….. ‘To say, indeed, that every individual star in the Milky Way, to the amount of eight or ten millions, is to have its place determined, and its motion watched, would be extravagant; but at least let samples be taken, at least let monographs of parts be made with powerful telescopes and refined instruments, that we may know what is going on in that abyss of stars, where at present imagination wanders without a guide!” Such is the enthusiastic call of one, whose father cleared the road by which we are introduced to the grandest phenomena of the stellar universe.'”

Locating Messier 58:

M59 is a telescopic only object and requires patience to find. Because the Virgo Galaxy field contains so many galaxies which can easily be mis-identified, it is sometimes easier to “hop” from one galaxy to the next! In this case, we need to start by locating bright Vindemiatrix (Epsilon Virginis) almost due east of Denebola.

Let’s starhop four and a half degrees west and a shade north of Epsilon to locate one of the largest elliptical galaxies presently known – M60. At a little brighter than magnitude 9, this galaxy could be spotted with binoculars, but stick with your telescope. In the same low power field (depending on aperture size) you may also note faint NGC 4647 which only appears to be interacting with M60.

In a smaller telescope, do not expect to see much. What will appear at low power is a tiny egg-shaped patch of contrast change with a brighter center. As aperture increases, a sharper nucleus will begin to appear as you move into the 4-6″ size range at dark sky locations, but elliptical galaxies do not show details. As with all galaxies, dark skies are a must!

Enjoy your own observations of the Virgo galaxy fields….

*The location of Messier 60 in the Virgo constellation. Credit: IAU*

And here are the quick facts on this Messier Object to help you get started:

Object Name: Messier 60
Alternative Designations: M60, NGC 4649
Object Type: E2 Galaxy
Constellation: Virgo
Right Ascension: 12 : 43.7 (h:m)
Declination: +11 : 33 (deg:m)
Distance: 60000 (kly)
Visual Brightness: 8.8 (mag)
Apparent Dimension: 7×6 (arc min)

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

November 17, 2017December 6, 2018 by Tammy Plotner

The Delphinus Constellation

This map shows Delphinus and Sagitta, both of which are near the bright star Altair at the bottom of the Summer Triangle. You can star hop from the Delphinus "diamond" to the star 29 Vulpecula and from there to the nova or center your binoculars between Eta Sagittae and 29 Vul. Stellarium

Welcome to another edition of Constellation Friday! Today, in honor of the late and great Tammy Plotner, we take a look at “the Dolphin” – the Delphinus constellation. Enjoy!

One of these is the northern constellation of Delphinus, which translates to “the Dolphin” in Latin. This constellation is located close to the celestial equator and is bordered by Vulpecula, Sagitta, Aquila, Aquarius, Equuleus, and Pegasus. Today, Delphinus is one of the 88 modern constellations recognized by the International Astronomical Union (IAU).

Name and Meaning:

According to classical Greek mythology, Delphinus represented a Dolphin. Once you “see” Delphinus, it is not hard to picture a small dolphin leaping from the waters of the Milky Way. According to Greek legend, Poseidon wanted to marry Amphitrite, a Nereid – or sea nymph. However, she hid from him. Poseidon sent out searchers, one of whom was named Delphinus.

*Delphinus is depicted on the left of this card from Urania’s Mirror (1825). Credit: Library of Congress/Sidney Hall*

Can you guess who found Amphitrite and talked her into marrying? You got it. In gratitude, Poseidon placed Delphinus’ image among the stars. Not a bad call since the Nereids were known to live in the silvery caves of the deep and the silvery Milky Way is so nearby!

In the other version of the myth, it was Apollo – the god of poetry and music – who placed the dolphin among the constellations for saving the life of Arion, a famed poet and musician. Arion was born on the island of Lesbos and his skill with the lyre made him famous in the 7th century BC.

History of Observation:

The small constellation of Delphinus was one of the original 48 constellations complied by Ptolemy in the Almagest in the 2nd century CE. In Chinese astronomy, the stars of Delphinus are located within the Black Tortoise of the North (Bei Fang Xuán Wu) – one of the four symbols associated with the Chinese constellations. Delphinus was also recognized by some cultures in Polynesia – particularly the people of Pukapuka and the Tuamotu Islands.

Notable Objects:

Located very near the celestial equator, this kite-like asterism is comprised of 5 main stars and contains 19 stellar members with Bayer/Flamsteed designations. It’s primary star, Alpha Delphini (aka. Sualocin), is a multiple star system located 240 light years from Earth which consists of an aging subgiant of 2.82 Solar masses, and a companion that cannot be discerned because it is too close to its primary and too faint.

Next is Beta Delphini (aka. Rotanev), a pair of stars located approximately 101 light years from Earth. This system is comprised of a F5 III class blue-white giant and a F5 IV blue-white subgiant. If you don’t think astronomers have a sense of humor, then you better think again! Sualocin and Rotanev were both named by Italian astronomer Nicolaus Cacciatore, who simply spelled the Latin form of name (Nicolaus Venator) backwards as a practical joke!

*Globular cluster NGC 6934. Credit: Hubble Space Telescope*

Epsilon Delphini (aka. Deneb Dulfim) is a spectral class B6 III blue-white giant star located about 358 light years from Earth. It’s traditional name comes from the Arabic ðanab ad-dulf?n, meaning “tail of the Dolphin”. Then there’s Rho Aquilae (aka. Tso Ke), a main sequence A2V white dwarf that is 154 light years distant. The star’s traditional name means “the left flag” in Mandarin, which refers to an asterism formed by Rho Aquilae and several stars in the constellation Sagittarius.

Delphinus is also home to numerous Deep Sky Objects, like the relatively large globular cluster NGC 6934. Located near Epsilon Delphini, this cluster is roughly 50,000 light years from Earth and was discovered by William Herschel on September 24th, 1785. Another globular cluster, known as NGC 7006, can be found near Gamma Delphini, roughly 137,000 light-years from Earth.

Delphinus is also home to the small planetary nebulas of NGC 6891 and NGC 6905 (the “Blue Flash Nebula”). Whereas the former is located near Rho Aquilae about 7,200 light years from Earth, the more notable Blue Flash Nebula (named because of its blue coloring) is located between 5,545 and 7,500 light-years from Earth.

Finding Delphinus:

Delphinus is bordered by the constellations of Vulpecula, Sagitta, Aquila, Aquarius, Equuleus and Pegasus. It is visible to all viewers at latitudes between +90° and -70° and is best seen at culmination during the month of September. Are you ready to start exploring Delphinus with binoculars? Then we’ll star with Alpha Delphini, whose name is Sualocin.

*The small planetary nebula of NGC 6891. Credit: Judy Schmidt*

Sualocin has seven components: A and G, a physical binary, and B, C, D, E, and F, which are optical and have no physical association with A and G. The primary is another rapid rotator star, whipping around at about 160 kilometers per second at its equator – or about 70 times faster than our Sun.

What it’s classification is, is confusing as well. It might a hydrogen-fusing main sequence star, and it subgiant that might just be starting to evolve. Wherever Suolocin lay in the scheme of things, there’s no use trying to resolve out the companion star, because it’s only a fraction of a second of arc away. However, Alpha’s nearby star, still makes for an interesting binocular view!

Now let’s look at Beta Delphini. Are you still ready for a smile? Good old Cacciatore wasn’t done yet. Beta’s name is Rotanev, which is a reversal of his Latinized family name, Venator. Here again we have a multiple star system. Rotanev has five components. Stars A and B are are a true physical binary star, while the others are simply optical companions. This time it’s cool to get out the telescope and split them!

Beta Delphini is a fine target for testing quality optics. At 97 light years from Earth, Rotanev’s components are only separated by about one stellar magnitude and 0.65 seconds of arc. By the way, in case you were wondering…. Nicolaus Venator was the assistant of the one and only Giuseppe Piazzi!

Are you ready for a look at Gamma Delphini? It’s the Y shape on the map. Here we have a binary star very worthy of even a small telescope. Located about a 101 light-years away from Earth, Gamma is one of the best known double stars in the night sky. The primary is a yellow-white dwarf star, a the secondary is an orange subgiant star. Both are separated by about one stellar magnitude and a very comfortable 9.2 seconds of arc apart.

*The globular cluster NGC 7006. Credit: NASA*

Regardless of their spectral class, take a look at how differently their colors appear in the telescope. While Gamma 1 (to the west) should by all rights be white, it often appears pale yellow orange, while Gamma 2 can appear yellow, green, or blue.

Before we put our binoculars away, let’s have a look at Delta Delphini – the figure “8” on our chart. Delta has no given name, but it has a partner. That’s right, it’s also a binary star. Its identical members are too close together to see separately and only by studying them spectroscopically were astronomers able to detect their 40.58 day orbital period.

Although Delta is officially classed as a type A (A7) giant star, it has a very strange low stellar temperature and an even stranger metal abundance. So what’s going on here? Chances are the Delta pair are really class F subgiants that have just ended core hydrogen fusion and both slightly variable. Do they orbit close to one another? You bet. So close, in fact, there orbit is only about the same distance as Mercury is from our Sun!

Now let’s take out the telescopes and have a look at NGC 7006 (RA 21h 1m 29.4 Dec +16 11′ 14.4) just a few arc minutes due east of Gamma. At magnitude 10, this small and powerful globular cluster might be mistaken for a stellar point in small telescopes at low power, for a very good reason… it’s very, very far away.

It is thought to be about 125 thousand light years from the galaxy’s core and over 135 thousand light years from us – far, far beyond the galaxy’s halo where it belongs. Even though it is a Class 1 globular, the most star dense in the Shapely?Sawyer classification system, and many observers comment that it looks more planetary nebula than it does a globular cluster!

Delphinus Constellation Map. Credit: IAU and Sky&Telescope magazine

Try NGC 6934 instead (RA 20 : 34.2 Dec +07 : 24) . This 50,000 light year distant globular cluster is much brighter and larger, though at Class VIII it doesn’t even come close to having as much stellar concentration. Discovered by Sir William Herschel on September 24, 1785, you’ll enjoy this one just for the rich star field that accompanies it. For larger telescope, you’ll enjoy the resolution and the study in contrasts between these two pairs.

Now let’s take a look at 12th magnitude planetary nebula, NGC 6891 (RA 20 : 15.2 Dec +12 : 42). Here we have an almost stellar appearance, but get tight on that focus and up the magnification to reveal its nature. This is anything but a star. As Martin A. Guerrero (et al) indicated in a 1999 study:

“Narrow-band and echelle spectroscopy observations show a great wealth of structures. The bright central nebula is surrounded by an attached shell and a detached outer halo. Both the inner and intermediate shells can be described as ellipsoids with similar major to minor axial ratios, but different spatial orientations. The kinematical ages of the intermediate shell and halo are 4800 and 28000 years, respectively. The inter-shell time lapse is in good agreement with the evolutionary inter-pulse time lapse. A highly collimated outflow is observed to protrude from the tips of the major axis of the inner nebula and impact on the outer edge of the intermediate shell. Kinematics and excitation of this outflow provide conclusive evidence that it is deflected during the interaction with the outer edge of the intermediate shell.”

If you’d like a real, big, telescope galaxy challenge, try galaxy group NGC 6927, NGC 6928 and NGC 6930. The brightest is NGC 6928 at magnitude 13.5, (RA 20h 32m 51.0s Dec: +09°55’49”). None of them will be easy… But what challenge is?

We have written many interesting articles about the constellation here at Universe Today. Here is What Are The Constellations?, What Is The Zodiac?, and Zodiac Signs And Their Dates.

Be sure to check out The Messier Catalog while you’re at it!

For more information, check out the IAUs list of Constellations, and the Students for the Exploration and Development of Space page on Canes Venatici and Constellation Families.

Sources:

November 10, 2017November 10, 2017 by Tammy Plotner

The Cygnus Constellation

The summer constellations of Cygnus and Lyra. The position of KIC 9832227 is shown with a red circle. It is in line with the three stars of the cross bar and, if it reaches 2nd magnitude in outburst, as it might, will be as bright as they are. Credit: calvin.edu

Welcome to another edition of Constellation Friday! Today, in honor of the late and great Tammy Plotner, we take a look at the “Swan” – the Cygnus constellation. Enjoy!

One of the constellations identified by Ptolemy was Cygnus, otherwise known as “the Swan”. The constellation is easy to find in the sky because it features a well-known asterism known as the Northern Cross. Cygnus was first catalogued the by Greek astronomer Ptolemy in the 2nd century CE and is today one of the 88 recognized by the IAU. It is bordered by the constellations of Cepheus, Draco, Lyra, Vulpecula, Pegasus and Lacerta.

Name and Meaning:

Because the pattern of stars so easily resembles a bird in flight, Cygnus the “Swan” has a long and rich mythological history. To the ancient Greeks, it was at one time Zeus disguising himself to win over Leda, and eventually father Gemini, Helen of Troy, and Clytemnestra. Or perhaps it is poor Orpheus, musician and muse of the gods, who when he died was transformed into a swan and placed in the stars next to his beloved lyre.

Artist’s conception of what Cygnus’ figure looks like, against the backdrop of stars that make up the constellation. Credit: Wendy Stenzel (first published on NASA Kepler website)

It could be king Cycnus, a relative of Phaethon, son of Apollo, who crashed dear old dad’s fiery sky chariot and died. Cygcus was believed to have driven up and down the starry river so many times looking for Phaethon’s remains that he was finally transformed into stars. No matter what legend you choose, Cygnus is a fascinating place… and filled with even more fascinating areas to visit!

History of Observation:

Because of its importance in ancient Greek mythology and astrology, the sprawling constellation of Cygnus was one of Ptolemy’s original 48 constellations. To Hindu astronomers, the Cygnus constellation is also associated with the “Brahma Muhurta” (“Moment of the Universe”). This period, which lasts from 4:24 AM to 5:12 AM, is considered to be the best time to start the day.

Cygnus is also highly significant to the folklore and mythology of many people in Polynesia, who also viewed it as a separate constellation. These include the people of Tonga, the Tuamatos people, the Maori (New Zealand) and the people of the Society Islands. Today, Cygnus is one of the official 88 modern constellations recognized by the IAU.

Notable Objects:

Flying across the sky in a grand position against the backdrop of the Milky Way, Cygnus consists of 6 bright stars which form an asterism of a cross comprised of 9 main stars and there are 84 Bayer/Flamsteed designated stars within its confines. It’s most prominent star, Deneb (Alpha Cygni), takes it name from the Arabic word dhaneb, which is derived from the Arabic phrase Dhanab ad-Dajajah, which means “the tail of the hen”.

*Cygnus as depicted in Urania’s Mirror, a set of constellation cards published in London c.1825. Surrounding it are Lacerta, Vulpecula and Lyra. Credit: Sidney Hall/US Library of Congress*

Deneb is a blue-white supergiant belonging to the spectral class A2 Ia, and is located approximately 1,400 light years from Earth. In addition to being the brightest star in Cygnus, it is one of the most luminous stars known. Being almost 60,000 times more luminous than our Sun and about 20 Solar masses, it is also one of the largest white stars known.

Deneb serves as a prototype for a class of variable stars known as the Alpha Cygni variables, whose brightness and spectral type fluctuate slightly as a result of non-radial fluctuations of the star’s surface. Deneb has stopped fusing hydrogen in its core and is expected to explode as a supernova within the next few million years. Together with the stars of Altair and Vega, Deneb forms the Summer Triangle, a prominent asterism in the summer sky.

Next up is Gamma Cygni (aka. Sadr), whose name comes from the Arabic word for “the chest”. It is also sometimes known by its Latin name, Pectus Gallinae, which means “the hen’s chest.” This star belongs to the spectral class F8 lad, making it a blue-white supergiant, and is located approximately 1,800 light years from Earth.

It can easily seen in the night sky at the intersection of the Northern Cross thanks to its apparent magnitude of 2.23, which makes it one of the brightest stars that can be seen in the night sky. It is also believed to be only about 12 million years old and consumes its nuclear fuel more rapidly because of its mass (12 Solar masses).

*Gamma Cygni (Sadr) is surrounded by a diffuse emission nebula, IC 1318, also known as the Sadr region or the Gamma Cygni region. Credit: Eric Larsen*

Then there’s Epsilon Cygni (ak. Glenah), an orange giant of the spectral class K0 III that is 72.7 light years distant. It’s traditional name comes from the Arabic word janah, which means “the wing” (this name is shared with Gamma Corvi, a star in the Corvus constellation). It is 62 times more luminous than the Sun and measures 11 Solar radii.

Delta Cygni (Rukh), is a triple star system in Cygnus, which is located about 165 light years away. The system consists of two stars lying close together and a third star located a little further from the main pair. The brightest component is a blue-white fast-rotating giant belonging to the spectral class B9 III. The star’s closer companion is a yellow-white star belonging to the spectral class F1 V, while the third component is an orange giant.

Last, there’s Beta Cygni (aka. Albireo) which is only the fifth brightest star in the constellation Cygnus, despite its designation. This binary star system, which appears as a single star to the naked eye, is approximately 380 light-years distant. The traditional name is the result of multiple translations and misunderstandings of the original Arabic name, minqar al-dajaja (“the hen’s beak”). It is one of the stars that form the Northern Cross.

The binary system consists of a yellow star which is itself a close binary star that cannot be resolved as two separate objects. Its second star is a fainter blue fast-rotating companion star with an apparent magnitude of 5.82 that is located 35 arc seconds apart from its primary.

*Albireo A, the primary star of Beta Cygni (which is itself a binary system). Credit: Henryk Kowalewski*

Cygnus is also home to a number of Deep Sky Objects. These include Messier 29 (NGC 6913), an open star cluster that is about 10 million years old and located about 4,000 light years from Earth. It can be spotted with binoculars a short distance away from Gamma Cygni – 1.7 degrees to the south and a little east.

Next up is Messier 39 (NGC 7092), another open star cluster that is located about 800 light-years away and is between 200 and 300 million years old. All the stars observed in this cluster are in their main sequence phase and the brightest ones will soon evolve to the red giant stage. The cluster can be found two and a half degrees west and a degree south of the star Pi-2 Cygni.

There is also the Fireworks Galaxy (NGC 6946), an intermediate spiral galaxy that is approximately 22.5 million light-years distant. The galaxy is located near the border of the constellation Cepheus and lies close to the galactic plane, where causes it to become obscured by the interstellar matter of the Milky Way.

Then there’s the famous X-ray source known as Cygnus X-1, which is one of the strongest that can be seen from Earth. Cygnus X-1 is notable for being the first X-ray source to be identified as a black hole candidate, with a mass 8.7 times that of the Sun. It orbits a blue supergiant variable star some 6,100 light-years away, which is one of two stars form a binary system.

Over time, an accretion disk of material brought from the star by a stellar wind has formed around Cygnus X-1, which is the source of its X-ray emissions.

Finding Cygnus:

Cygnus is visible to all observers at latitudes between +90° and -40° and is best seen at culmination during the month of September. For a period of 15 days around the peak date of August 20, watch for the Kappa Cygnid meteor shower. This annual meteor shower has a radiant near the bright star Deneb and an average fall rate of about 12 meteors per hour. It is noted to have many bright fire balls called “bolides” and the best time to watch is when the constellation is directly overhead.

Because Cygus is so rich in things to visit, we shall only touch very briefly on just a few. Let’s begin with our unaided eye as we take a look at the brightest star of the constellation, Alpha Cygni – Deneb. Here we have not only an extremely luminous blue super giant star – but a pulsing variable star, too. Its changes are minor – only about 1/10 of a stellar magnitude, but Deneb is its own prototype.

Its stellar oscillations are very complex, consisting of multiple pulsation frequencies as well as a fundamental one. This means changes in brightness occur between 5 and 10 days apart, but that’s a good thing. If the changes weren’t small, Deneb would blow itself to bits!

If you are looking at Cygnus for an area well away from city lights on a night when there is no Moon, look just northwest of Deneb for the North America Nebula (NGC 7000). This is an excellent emission nebula that covers as much area of the sky as 10 full Moons! At 3 full degrees, you’ll be looking for a vague, misty patch of silver-ness that about as broad as your thumb held at arm’s length.

While telescopes and binoculars are grand, remember this particular region is so large that you can easily over magnify it and often your unaided eye is all you need to catch this elusive interstellar cloud of ionized hydrogen (H II region). Now, get out your binoculars and let’s dance!

Messier 29 is very easy and bright and you can find it about a fingerwidth south and a little east of Gamma Cygni – the “8” shape on our map. This open cluster of stars has just a handful of bright members and will look like a small rendition of the “Big Dipper”. M29 is about 7,200 light years away from Earth, so the fact we can see it at all in binoculars is pretty impressive! Now, try Messier 39.

You’ll find this one about a fingerwidth west and southwest of Pi2, which looks like TT2 on our map. This galactic star cluster is far brighter and richer than the last. It will show as a triangle shape with bright stars in each corner and a couple of dozen fainter stars captured within the center. M39 is only about 800 light years away from our solar system, but it could be as much as 300 million years old!

Don’t put your binoculars away just yet. You’ve got to visit Omega 2 before you stop! Its name is Ruchbah and it’s a double star about 500 light years from Earth, consisting of a magnitude 5.44 star of spectral class M2 and a 6.6 magnitude star of spectral class A0. The stars are well separated at 256″ apart and can be seen in binoculars and totally glorious in a telescope. Because of the color contrast (red main star and blue companion), Ruchba is a beautiful object for amateur astronomers.

*The northern Cygnus constellation. Credit: IAU*

Now try Beta Cygni – Albireo. It is also known as one of the most attractive and colorful double stars in the sky. Beautiful Beta 1 is an orange giant K star and Beta 2 is a main-sequence B star of a soft, blue hue. If you can’t separate them in your binoculars, use a telescope! This seasonal favorite is one that’s not to be missed! Now, let’s try a couple objects for the telescope.

One of the true prizes of the Cygnus region for any telescope is the Holy Veil (NGC 6960, 6962, 6979, 6992, and 6995). You’ll find it just south of Epsilon Cygni and the easiest segment to find is 6960, which runs through the star 52 Cygni. This is an ancient supernova remnant covering approximately 3 degrees of the sky and an experience you won’t soon forget if you are viewing from a dark sky site.

The source supernova exploded some 5,000 to 8,000 years ago and it is simply amazing to think that anything remains to be seen. It was discovered on 1784 September 5 by William Herschel. He described the western end of the nebula as “Extended; passes thro’ 52 Cygni… near 2 degree in length.” and described the eastern end as “Branching nebulosity… The following part divides into several streams uniting again towards the south.”

Even though it is any where from from 1,400 to 2,600 light-years light years away, you’ll find long and wondrous tongues of material to capture your interest and delight your eye and you follow them to their ends!

More challenging is the Crescent Nebula (NGC 6888 or Caldwell 27) located at RA 20h 12m 7s Dec +38 21.3′. This is an emission nebula fueled by a Wolf-Rayet star located about 5000 light years away. It is formed by the fast stellar wind careening off illuminating the slower moving wind ejected by the star when it went into the red giant star stage. What’s left is a collision… a shell and two shock waves… one moving outward and one moving inward. A what a grand one it is!

*The Fireworks Galaxy (NGC 6946) taken by the Subaru Telescope. Credit: NAOJ/Robert Gendler*

For galaxy fans, you have got to point your telescope towards NGC 6946, the “Fireworks Galaxy” (RA 20h 34m 52.3s Dec +60 09 14). Who cares if this barred spiral galaxy 10 million light years away? This is one supernovae active baby! At one time, it was widely believed that NGC 6946 was a member of our Local Group; mainly because it could be easily resolved into stars.

There was a reddening observed in it, believed to be indicative of distance – but now know to be caused by interstellar dust. But it isn’t the shrouding dust cloud that makes NGC 6946 so interesting, it’s the fact that so many supernova and star-forming events have sparkled in its arms in the last few years that has science puzzled! So many, in fact, that they’ve been recorded every year or two for the last 60 years…

Now, for the really cool part – understanding barred structure. Thanks to the Hubble Space Telescope and a study of more than 2,000 spiral galaxies – the Cosmic Evolution Survey (COSMOS) – astronomers understand that barred spiral structure just didn’t occur very often some 7 billion years ago in the local universe. Bar formation in spiral galaxies evolved over time.

A team led by Kartik Sheth of the Spitzer Science Center at the California Institute of Technology in Pasadena discovered that only 20 percent of the spiral galaxies in the distant past possessed bars, compared with nearly 70 percent of their modern counterparts. This makes NGC 6946 very rare, indeed… Since its barred structure was noted back in Herschel’s time and its age of 10 billion years puts it beyond what is considered a “modern” galaxy.

It that all there is? Not hardly. Try NGC 6883, an open cluster located about 3 degrees east/northeast of Eta Cygni. It’s a nice, tight cluster that involves a well-resolved double star and a bonus open cluster – Biurakan 2 – as well. Or how about NGC 6826 located about 1.3 degrees east/northeast of Theta. This one is totally cool… the “Blinking Planetary”!

This planetary nebula is fairly bright and so is the central star… but don’t stare at it, or it will disappear! Look at it averted and the central star will appear again. Neat trick, huh? Now try NGC 6819 about 8 degrees west of Gamma. Here you’ll find a very rich, bright open cluster of about 100 stars that’s sure to please. It’s also known as Best 42!

There’s many more objects in Cygnus than just what’s listed here, so grab yourself a good star chart and fly with the “Swan”!

We have written many interesting articles about the constellation here at Universe Today. Here is What Are The Constellations?, What Is The Zodiac?, and Zodiac Signs And Their Dates.

Be sure to check out The Messier Catalog while you’re at it!

For more information, check out the IAUs list of Constellations, and the Students for the Exploration and Development of Space page on Canes Venatici and Constellation Families.

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