Posted on 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.

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 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)

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:

Posted on 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.

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 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)

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:

Posted on 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.

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 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)

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:

Posted on by Tammy Plotner

Messier 59 – the NGC 4621 Elliptical Galaxy

Messier 60, Messier 59 and Messier 58. Credit: Wikisky

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the spiral galaxy known as Messier 59.

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 elliptical galaxy known as Messier 59 (aka. NGC 4621). This galaxy is located approximately 60 million light-years from Earth in the direction of the southern Virgo constellation. Sitting just a few degrees away Messier 60, and bordered at a distance by Messier 58, this galaxy is visible using smaller instruments, but is best observed using a larger telescope.

Atlas image of Messier 59 obtained by the Two micron All Sky Survey (2MASS). Credit: 2MASS/NASA/UMass

Description:

Located about 60 million light years away and spanning about 90 million light years of space, but what exactly is its type? Says Takao Mizuno (et al) in their 1996 study:

“We decomposed two-dimensionally an elliptical galaxy, NGC 4621, which shows deviations from the brightness distribution law. We have found that its brightness distribution can be reproduced by three components possessing constant ellipticities of the residuals in the circular region of radius. The component obeying the aw has 62% of the total light, and, hence, is the main body of this elliptical galaxy.” So it might not be the biggest or the brightest of the group, but it is home to nearly 2000 globular clusters. This isn’t news when it comes to this galaxy type, but what is news is how they rotate… the wrong way!

“We present adaptive optics assisted OASIS integral field spectrography of the S0 galaxy NGC 4621. Two-dimensional stellar kinematical maps (mean velocity and dispersion) reveal the presence of a 60 pc diameter counter-rotating core (CRC), the smallest observed to date.” says Fabien Wernli (et al), “The OASIS data also suggests that the kinematic center of the CRC is slightly offset from the center of the outer isophotes. This seems to be confirmed by archival HST/STIS data. We also present the HST/WFPC2 V-I colour map, which exhibits a central elongated red structure, also slightly off-centered in the same direction as the kinematic centre. Although the stellar velocities are reasonably fitted, including the region of the counter-rotating core, significant discrepancies between the model and the observations demonstrate the need for a more general model.”

What could account for such unusual behavior? Try a quiet black hole! As J. M. Wrobel (et al) indicated in their 2008 study:

“The nearby elliptical galaxies NGC 4621 and NGC 4697 each host a supermassive black hole. Analysis of archival Chandra data and new NRAO Very Large Array data shows that each galaxy contains a low-luminosity active galactic nucleus (LLAGN), identified as a faint, hard X-ray source that is astrometrically coincident with a faint 8.5-GHz source. The black holes energizing these LLAGNs have Eddington ratios placing them in the so-called quiescent regime. The emission from these quiescent black holes is radio-loud, suggesting the presence of a radio outflow. Also, application of the radio-X-ray-mass relation from Yuan & Cui for quiescent black holes predicts the observed radio luminosities to within a factor of a few. Significantly, that relation invokes X-ray emission from the outflow rather than from an accretion flow. The faint, but detectable, emission from these two massive black holes is therefore consistent with being outflow-dominated.”

The M59 spiral galaxy. Credit: NOAO

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.” Charles Messier would independently recover it four days later and state in his notes:

“Nebula in Virgo and in the neighborhood of the preceding [M58], on the parallel of epsilon [Virginis], which has served for its [position] determination: it is of the same light as the above, equally faint. M. Messier reported it on the Chart of the Comet of 1779.”

While both William and John Herschel would also observe it, it sometimes confounds me that they didn’t seem to notice all the other galaxies around it! Fortunately for historic record, Admiral Smyth did:

“A fine field is exhibited under the eye-piece, which magnifies 93 times, just as this object [M60 with NGC 4647] enters, because the bright little nebula 59 M. is quitting the np [north preceding, NW] verge, and another small one is seen in the upper part, H. 1402 [NGC 4638]: in fact, four nebulae at once.”

Locating Messier 58:

M59 is a telescope-only object and requires patience to find. Because the Virgo Galaxy field contains so many galaxies which can easily be misidentified, 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. Then starhop four and a half degrees west and a shade north of Epsilon to locate one of the largest elliptical galaxies presently known – M60.

The location of M59, which sits between M58 and M60 in the direction of the Virgo constellation. Credit: IAU

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. Also in the field to the west (the direction of drift) is the Messier we’re looking for, bright cored elliptical galaxy M59.

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 journey around the Virgo Galaxy Field!

Object Name: Messier 59
Alternative Designations: M59, NGC 4621
Object Type: E5 Galaxy
Constellation: Virgo
Right Ascension: 12 : 42.0 (h:m)
Declination: +11 : 39 (deg:m)
Distance: 60000 (kly)
Visual Brightness: 9.6 (mag)
Apparent Dimension: 5×3.5 (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:

Posted on by Tammy Plotner

Messier 58 – the NGC 4579 Barred Spiral Galaxy

The galaxies of Messier 58, Messier 59, Messier 60, Messier 87, Messier 89 and Messier 90. Credit: Wikisky

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the barred spiral galaxy, Messier 58.

In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. In time, he would come to compile a list of approximately 100 of these objects, with the purpose of making sure that astronomers did not mistake them for comets. However, this list – known as the Messier Catalog – would go on to serve a more important function, becoming one of the first catalogs of Deep Sky Objects.

One of these objects is the intermediate barred spiral galaxy known as Messier 58, which is located approximately 68 million light years away in the Virgo constellation. In addition to being one of just four barred spiral galaxies in the Messier Catalog, it is also one of the brightest galaxies in the Virgo Supercluster. Due to its proximity in the sky to other objects in the Virgo Galaxy Field, it can be seen only with the help of a telescope or a pair of large binoculars.

Description:

This beautiful old barred spiral galaxy located approximately 68 million light-years from Earth. Although it might appear pretty plain, it has some great things going for it… namely an active galactic nucleus. As Marcella Contini indicated in a 2004 study:

“We have modelled the low-luminosity active galactic nuclei (AGN) NGC 4579 by explaining both the continuum and the line spectra observed with different apertures. It was found that the nuclear emission is dominated by an AGN such that the flux from the active centre (AC) is relatively low compared with that of the narrow emission-line region (NLR) of Seyfert galaxies. However, the contribution of a young starburst cannot be neglected, as well as that of shock-dominated clouds with velocities of 100, 300 and 500kms-1. A small contribution from an older starburst with an age of 4.5 Myr, probably located in the external nuclear region, is also found. HII regions appear in the extended regions, where radiation and shock-dominated clouds prevail.

“The continuum SED of NGC 4579 is characterized by the strong flux from an old stellar population. Emissions in the radio range show synchrotron radiation from the base of the jet outflowing from the accretion disc within 0.1 pc from the active centre. Radio emission within intermediate distances is explained by the bremsstrahlung from gas downstream of low-velocity shocks reached by a relatively low radiation flux from the AC. In extended regions the radio emission is synchrotron radiation created by the Fermi mechanism at the shock front. The shocks are created by collision of clouds with the jet. All types of emissions observed at different radius from the centre can be reconciled with the presence of the jet.”

The Messier 58 barred spiral galaxy. Credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona

Yet where is this gas traveling to and why? According to 2014 study by S. Garcia-Burillo (et al):

“We created a complete gravity torque map of the disk of the LINER/Seyfert 1.9 galaxy NGC 4579. We quantify the efficiency of angular momentum transport and search for signatures of secular evolution in the fueling process from r ~ 15 kpc down to the inner r ~ 50 pc around the active galactic nucleus (AGN). The derived gravity torque budget in NGC 4579 shows that inward gas flow is occurring on different spatial scales in the disk. In the outer disk, the decoupling of the spiral allows the gas to efficiently populate the UHR region, and thus produce net gas inflow on intermediate scales. The co rotation barrier seems to be overcome by secular evolution processes. The gas in the inner disk is efficiently funneled by gravity torques down to r ~ 300 pc. Closer to the AGN, gas feels negative torques due to the combined action of the large-scale bar and the inner oval. The two m=2 modes act in concert to produce net gas inflow down to r ~ 50 pc, providing clear smoking gun evidence of inward gas transport on short dynamical timescales.”

What causes inward transport of gases? Why, a massive gravity pull of course. And what could be more gravitational attractive than a black hole! As Eliot Quataert (et al) indicated in their 1999 study:

“M81 and NGC 4579 are two of the few low-luminosity active galactic nuclei which have an estimated mass for the central black hole, detected hard X-ray emission, and detected optical/UV emission. In contrast to the canonical “big blue bump,” both have optical/UV spectra which decrease with increasing frequency in a plot. Barring significant reddening by dust and/or large errors in the black hole mass estimates, the optical/UV spectra of these systems require that the inner edge of a geometrically thin, optically thick, accretion disk lies at roughly 100 Schwarzschild radii. The observed X-ray radiation can be explained by an optically thin, two temperature, advection-dominated accretion flow at smaller radii.”

Galaxy NGC 4579 was captured by the Spitzer Infrared Nearby Galaxy Survey (SINGS) Legacy Project using the Spitzer Space Telescope’s Infrared Array Camera (IRAC). In this image, the red structures are areas where gas and dust are thought to be forming new stars, while the blue light comes from mature stars. This SINGS image is a four-channel, false-color composite, where blue indicates emission at 3.6 microns, green corresponds to 4.5 microns, and red to 5.8 and 8.0 microns. The contribution from starlight (measured at 3.6 microns) in this picture has been subtracted from the 5.8 and 8 micron images to enhance the visibility of the dust features.

Messier 58 (NGC 4579), as imaged by the Spitzer Infrared Nearby Galaxy Survey (SINGS) Legacy Project using the Spitzer Space Telescope’s Infrared Array Camera (IRAC). Credit: NASA/JPL-Caltech/R. Kennicutt (University of Arizona) and the SINGS Team

History of Observation:

When Charles Messier discovered this one on April 15, 1779, I’m sure he didn’t know he was looking back into time when he wrote:

“Very faint nebula discovered in Virgo, almost on the same parallel as Epsilon, 3rd mag. The slightest light for illuminating the micrometer wires makes it disappear. M. Messier reported it on the chart of the Comet of 1779, which is located in the volume of the Academy for the same year.”

Messier 58 may not have been a comet, but it certainly was another distant cousin of our own Milky Way!

Locating Messier 58:

Finding M58 requires a telescope or large binoculars, and lots of patience. Because the Virgo Galaxy field contains so many galaxies which can easily be misidentified, 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 hop 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. Also in the field to the west (the direction of drift) is our next Messier, bright cored elliptical M59. Now we will need to continue about an average eyepiece field of view, or a degree further west of this group to bring you to our “galactic twin”, fainter M58.

The location of M58, in the direction of the Virgo constellation. Credit: IAU

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. As aperture increases, so does detail and a bright nucleus will begin to appear as you move into the 4-6″ size range and dark sky locations. As with all galaxies, dark skies are a must!

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

Object Name: Messier 58
Alternative Designations: M58, NGC 4579
Object Type: SBc Galaxy
Constellation: Virgo
Right Ascension: 12 : 37.7 (h:m)
Declination: +11 : 49 (deg:m)
Distance: 60000 (kly)
Visual Brightness: 9.7 (mag)
Apparent Dimension: 5.5×4.5 (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:

Posted on by Tammy Plotner

Messier 57 – The Ring Nebula

Hubble image of the Ring Nebula (aka. Messier 57). Credit: NASA/ESA/ Hubble Heritage (STScI/AURA) – ESA /Hubble Collaboration
Hubble image of the Ring Nebula (aka. Messier 57). Credit: NASA/ESA/ Hubble Heritage (STScI/AURA) – ESA /Hubble Collaboration

Welcome back to Messier Monday! We continue our tribute to our dear friend, Tammy Plotner, by looking at the the Big Ring itself, the planetary nebula known as Messier 57. Enjoy!

In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. In time, he would come to compile a list of approximately 100 of these objects, with the purpose of making sure that astronomers did not mistake them for comets. However, this list – known as the Messier Catalog – would go on to serve a more important function.

One of these objects is known as Messier 57, a planetary nebula that is also known as the Ring Nebula. This object is located about 2,300 light years from Earth in the direction of the Lyra constellation. Because of its proximity to Vega, the brightest star in Lyra and one of the stars that form the Summer Triangle, the nebula is relatively easy to find using binoculars or a small telescope.

What You Are Looking At:

Here you see the remainders of a sun-like star… At one time in its life, it may have had twice the mass of Sol, but now all that’s left is a white dwarf that burns over 100,000 degrees kelvin. Surrounding it is an envelope about 2 to 3 light years in size of what once was its outer layers – blown away in a cylindrical shape some 6000 to 8000 years ago. Like looking down the barrel of a smoking gun, we’re looking back in time at the end of a Mira-like star’s evolutionary phase.

It’s called a planetary nebula, because once upon a time before telescopes could resolve them, they appeared almost planet-like. But, as for M57, the central star itself is no larger than a terrestrial planet! The tiny white dwarf star, although it could be as much as 2300 light years away, has an intrinsic brightness of about 50 to 100 times that of our Sun.

One of the most beautiful features of M57 is the structure in the ring itself, sometimes called braiding – but scientifically known as “knots” in the gaseous structure. As C.R. O’Dell (et al) indicated in their 2003 study:

“We have studied the closest bright planetary nebulae with the Hubble Space Telescope’s WFPC2 in order to characterize the dense knots already known to exist in NGC 7293. We find knots in all of the objects, arguing that knots are common, simply not always observed because of distance. The knots appear to form early in the life cycle of the nebula, probably being formed by an instability mechanism operating at the nebula’s ionization front. As the front passes through the knots they are exposed to the photoionizing radiation field of the central star, causing them to be modified in their appearance. This would then explain as evolution the difference of appearance like the lacy filaments seen only in extinction in IC 4406 on the one extreme and the highly symmetric “cometary” knots seen in NGC 7293. The intermediate form knots seen in NGC 2392, NGC 6720, and NGC 6853 would then represent intermediate phases of this evolution.”

However, examining things like planetaries nebulae in different wavelengths of light can tell us so much more about them. Behold the beauty when see through the Spitzer Space Telescope! As M.M. Roth explained in a 2007 study:

“Emission nebulae like H II regions, Planetary Nebulae, Novae, Herbig Haro objects etc. are found as extended objects in the Milky Way, but also as point sources in other galaxies, where they are sometimes observable out to very large distances due to the high contrast provided by some prominent emission lines. It is shown how 3D spectroscopy can be used as a powerful tool for observations of both large resolved emission nebulae and distant extragalactic objects, with special emphasis on faint detection limits.”

History of Observation:

This deep space object was first discovered in early January 1779 by Antoine Darquier who wrote in his notes:

“This nebula, to my knowledge, has not yet been noticed by any astronomer. One can only see it with a very good telescope, it is not resembling any of those [nebula] already known; it has the apparent dimension of Jupiter, is perfectly round and sharply limited; its dull glow resembles the dark part of the Moon before the first and after the last quarter. Meanwhile, the center appears a bit less pale than the remaining part of its surface.”

Although Darquier did not post a date, it is believed his observation preceded Messier’s independent recovery made on January 31, 1779 when he states that Darquier picked it up before him:

“A cluster of light between Gamma and Beta Lyrae, discovered when looking for the Comet of 1779, which has passed it very close: it seems that this patch of light, which is round, must be composed of very small stars: with the best telescopes it is impossible to distinguish them; there stays only a suspicion that they are there. M. Messier reported this patch of light on the Chart of the Comet of 1779. M. Darquier, at Toulouse, discovered it when observing the same comet, and he reports: ‘Nebula between gamma and beta Lyrae; it is very dull, but perfectly outlined; it is as large as Jupiter and resembles a planet which is fading’.”

A few years later, Sir William Herschel would also observe Messier Object 57 with his superior telescope and in his private notes he writes:

“Among the curiosities of the heavens should be placed a nebula, that has a regular, concentric, dark spot in the middle, and is probably a Ring of stars. It is of an oval shape, the shorter axis being to the longer as about 83 to 100; so that, if the stars form a circle, its inclination to a line drawn from the sun to the center of this nebula must be about 56 degrees. The light is of the resolvable kind [i.e., mottled], and in the northern side three very faint stars may be seen, as also one or two in the southern part. The vertices of the longer axis seem less bright and not so well defined as the rest. There are several small stars very bear, but none seems to belong to it.”

Admiral Smyth would go on in later years to add his own detailed observations to history’s records:

“This annular nebula, between Beta and Gamma on the cross-piece of the Lyre, forms the apex of a triangle which it makes with two stars of the 9th magnitude; and its form is that of an elliptic ring, the major axis of which trends sp to nf [SW to NE]. This wonderful object seems to have been noted by Darquier, in 1779; but neither he nor his contemporaries, Messier and Méchain, discerned its real form, seeing in this aureola of glory only “a mass of light in the form of a planetary disc, very dingy in colour.”

“Sir W. Herschel called it a perforated resolvable nebula, and justly ranked it among the curiosities of the heavens. He considered the vertices of the longer axis less bright and not so well defined as the rest; and he afterwards added: ‘By the observations of the 20-feet telescope, the profundity of the stars, of which it probably consists, must be of a higher than the 900th order, perhaps 950.'”

“This is a vast view of the ample and inconceivable dimensions of the spaces of the Universe; and if the oft-cited cannon-ball, flying with the uniform velocity of 500 miles an hour, would require millions of years to reach Sirius, what an incomprehensible time it would require to pass so overwhelming an interval as 950 times the distance! And yet, could we arrive there, by all analogy, no boundary would meet the eye, but thousands and ten thousands of other remote and crowded systems would still bewilder the imagination.

“In my refractor this nebula has a most singular appearance, the central vacuity being black, so as to countenance the trite remark of its having a hole through it. Under favourable circumstances, when the instrument obeys the smooth motion of the equatorial clock, it offers the curious phenomenon of a solid ring of light in the profundity of space. The annexed sketch affords a notion of it. Sir John Herschel, however, with the superior light of his instrument, found that the interior is far from absolutely dark. “It is filled,’ he says, ‘with a feeble but very evident nebulous light, which I do not remember to have been noticed by former observers.'”

Since Sir John’s observation, the powerful telescope of Lord Rosse has been directed to this subject, and under powers 600, 800, and 1000, it displayed very evident symptoms of resolvability at its minor axis. The fainter nebulous matter which fills it, was found to be irregularly distributed, having several stripes or wisps in it, and the regularity of the outline was broken by appendages branching into space, of which prolongations the brightest was in the direction of the major axis.

Locating Messier 57:

M57 is a breeze to locate because it is positioned between Beta and Gamma Lyrae (the westernmost pair of the lyre’s stars), at about one-third the distance from Beta to Gamma. While it is easily seen in binoculars, it is a little difficult to identify because of its small size, so binoculars must be very steady to distinguish it from the surrounding star field.

In even a small telescope at minimum power, you’ll quickly notice a very small, but perfect ring structure which takes very well to magnification. Despite low visual brightness, M57 actually takes well to urban lighting conditions and can even be spied during fairly well moonlit nights. Larger aperture telescopes will easily see braiding in the nebula structure and often glimpse the central star. May you also see the many faces of the “Ring”!

The location of Messier 57 in the Lyra Constellation. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

And here are the quick facts on Messier 57 to help you get started:

Object Name: Messier 57
Alternative Designations: M57, NGC 6720, the “Ring Nebula”
Object Type: Planetary Nebula
Constellation: Lyra
Right Ascension: 18 : 53.6 (h:m)
Declination: +33 : 02 (deg:m)
Distance: 2.3 (kly)
Visual Brightness: 8.8 (mag)
Apparent Dimension: 1.4×1.0 (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:

Posted on by Tammy Plotner

Messier 56 – the NGC 6779

Messier 56 and Messier 57 (the Ring Nebula). Credit: Wikisky

Welcome back to Messier Monday! We continue our tribute to our dear friend, Tammy Plotner, by looking at the the globular star cluster known as Messier 56. Enjoy!

In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. In time, he would come to compile a list of approximately 100 of these objects, with the purpose of making sure that astronomers did not mistake them for comets. However, this list – known as the Messier Catalog – would go on to serve a more important function.

One of these objects is Messier 56, a globular star cluster located in the small northern constellation of Lyra, roughly 32,900 light years from Earth. Measuring roughly 84 light-years in diameter, this cluster has an estimated age of 13.70 billion years. It is also relatively easy to spot because of its proximity to well-known asterisms like the celestial Swan, the Northern Cross, and the bright star Vega.

Description:

Spanning about 85 light years in diameter, this incredible ball of stars is moving towards planet Earth at a speed of 145 kilometers per second… yet still remains about 32,900 light-years away. As one of the less dense of the Milky Way’s halo globulars, it is also less dense in variable stars – containing only perhaps a dozen. But out of that twelve, there a very special one… a Cepheid bright enough to be followed with amateur instruments. However, astronomers never stopped looking for the curious – and they found what they were looking for!

NASA/ESA Hubble image of the globular star cluster known as Messier 56. Credit: NASA/ESA/HST/Gilles Chapdelaine

The CURiuos Variables Experiment (CURVE) was performed on M56 in 2008. As P. Pietrukowicz (et al) wrote of the cluster in the accompanying study:

“We surveyed a 6.5’×6.5′ field centered on the globular cluster M56 (NGC 6779) in a search for variable stars detecting seven variables, among which two objects are new identifications. One of the new variables is an RRLyrae star, the third star of that type in M56. Comparison of the new observations and old photometric data for an RV Tauri variable V6 indicates a likely period change in the star. Its slow and negative rate of -0.005±0.003 d/yr would disagree with post-AGB evolution, however this could be a result of blue-loop evolution and/or random fluctuations of the period.”

But could other things exist inside M56? Events, perhaps, like nova? As astronomer Tim O’Brien wrote:

“Classical nova outbursts are the result of thermonuclear explosions on the surface of a white dwarf star in a close binary system. Material from the other star in the system (one not unlike our own sun) falls onto the surface of the white dwarf over thousands of years. The pressure at the base of this layer of accreted material builds up until thermonuclear reactions begin explosively. An Earth’s mass or more of material is ejected from the surface of the white dwarf at speeds of a few hundred to a few thousand kilometres per second. Old novae are therefore surrounded by shells of ejected matter illuminated by the light from the central binary system.”

And as M.E.L. Hopwood (et al.) wrote in a 2000 study:

“We report the possible detection of diffuse X-ray emission in the environment of NGC 6779, and find the emission to be well aligned with the proper motion of the cluster. The position of the emission suggests we are observing heated ISM in the wake of the cluster that could be the result of an interaction between the intracluster medium and the halo gas surrounding it.”

Globular cluster Messier 56 in Lyra. Credit: Wikipedia Commons/Hewholooks

History of Observation:

Charles Messier first discovered M56 on January 23rd, 1779. As he wrote of his discovery at the time:

“Nebula without stars, having little light; M. Messier discovered it on the same day as he found the comet of 1779, January 19. On the 23rd, he determined its position by comparing it with the star 2 Cygni, according to Flamsteed: it is near the Milky Way; and close to it is a star of 10th magnitude. M. Messier reported it on the chart of the comet of 1779.”

However, it would be Sir William Herschel who revealed its true nature in 1807. In his private notes he writes: “The 56th of the Connoiss. is a globular cluster of very compressed and very small stars. They are gradually more compressed towards the centre.” His son John would go on to observe it many times, even after cataloging it! His best description reads: “Large; round; very gradually brighter toward the middle. I see the stars which are very small and of different sizes. It fades gradually away to the borders.”

As always, it would be Admiral Smyth who would be perhaps a bit more descriptive when he included in his observing notes:

“A globular cluster, in a splendid field, between the eastern joke of Lyra’s frame and the Swan’s head: it is 5 1/4 deg distant from Beta Lyrae, on the south-east line leading to Beta Cygni, which is about 3 1/2 deg further. This object was first registered by M. Messier in 1778, and, from his imperfect means, described as a nebula of feeble light, without a star. In 1784, it was resolved by Sir William Herschel, who, on gauging, considered its profundity to be of the 344th order.”

Messier 56 location. Credit: IAU/Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

Locating Messier 56:

Finding M56 isn’t too hard since it’s located about half-way between Beta Cygni (Albireo) and Gamma Lyrae. In both binoculars and finder scope, you will see a triangle of stars when progressing from Gamma towards the southeast that will almost point directly at it! Because M56 isn’t particularly large or bright, it does require dark skies – but makes a great object for both binoculars and small telescopes.

Enjoy this pincushion of stars! And here are the quick facts on this Messier Object to help you get started”

Object Name: Messier 56
Alternative Designations: M56, NGC 6779
Object Type: Class X Globular Cluster
Constellation: Lyra
Right Ascension: 19 : 16.6 (h:m)
Declination: +30 : 11 (deg:m)
Distance: 32.9 (kly)
Visual Brightness: 8.3 (mag)
Apparent Dimension: 8.8 (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:

Posted on by Tammy Plotner

Messier 55 – the NGC 6809 Globular Star Cluster

The globular star cluster Messier 55 in the constellation of Sagittarius (The Archer) was obtained in infrared light with the VISTA survey telescope at ESO’s Paranal Observatory in Chile. This vast ball of ancient stars is located at a distance of about 17 000 light-years from Earth. Credit: ESO/J. Emerson/VISTA

Welcome back to Messier Monday! We continue our tribute to our dear friend, Tammy Plotner, by looking at the “Summer Rose Star”, other known as the globular star cluster of Messier 55. Enjoy!

In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. In time, he would come to compile a list of approximately 100 of these objects, with the purpose of making sure that astronomers did not mistake them for comets. However, this list – known as the Messier Catalog – would go on to serve a more important function.

One of these objects is Messier 55, a globular star cluster located in the Sagittarius Constellation. Also known as the “Summer Rose Star”, this cluster is located 17,600 light-years from Earth and spans about 100 light-years in diameter. While it can be seen with binocular, resolving its individual stars can only be done with a small telescope and finderscope.

Description:

Located some 17,300 light years from planet Earth and spanning nearly 100 light years in diameter, this loose appearing ball of stellar points may not seem concentrated – but its home to tens of thousands stars. Does anyone really take the time to count them? You bet. M.J. Irwin and V. Trimble did just that during their 1984 study of Messier 55:

“We report star counts, as a function of position and apparent magnitude, in the rich, relatively open southern globular cluster NGC 6809 (M55). Three AAO 150arcsec plates were scanned by the Automatic Plate Measuring System (APM) at the Institute of Astronomy, Cambridge, and 20825 images were counted by its associated software. Previously known features of rich globular clusters which appear in the raw counts include a flattening of the luminosity function, increased central concentration of bright stars relative to faint ones (normally interpreted as mass segregation), and mild deviations in radial profile from King models. Crowding of the field, which causes the counting procedure to miss faint stars preferentially near the cluster center, contributes to all of these, and may be responsible for all of the apparent mass segregation, but not for all of the other two effects.”

Globular cluster Messier 55 (M55, or NGC 6809) in the constellation Sagittarius, as imaged by the ESO 3.6-metre telescope on La Silla. Release date: 3 December 2009. Credit: ESO

But just want good does counting the stars do? Well, knowing how many stars are within a given area helps astronomers compute other things as well, like chemical abundances. Said Carlos Alvarez and Eric Sandquist in their 2004 study:

“We have compiled the asymptotic giant, horizontal, and upper red giant branch (AGB, HB, and RGB) stars in the globular cluster M55 (NGC 6809). Using the star counts and the R-parameter we compute the initial helium abundance. The ratio is unusually high for a globular cluster, being almost 2 away from the predicted values, and the highest recorded for a massive globular cluster. We argue that M55’s particular HB morphology and metallicity have produced long-lived HB stars that are not too blue to avoid producing AGB stars. This result hints that we are able to map evolutionary effects on the HB. Finally, although we find no evidence of variations in HB morphology with distance from the center of the cluster, the red HB stars are significantly less concentrated than the majority of HB stars, and the bluest HB stars are more centrally concentrated.”

Studying globular clusters photometrically also gives astronomers the advantage of comparing them to others, to see how each evolves. As P. Richter (et al) indicated in their 1999 study:

“We present Stroemgren CCD photometry for the two galactic globular clusters M55 (NGC 6809) and M22 (NGC 6656). The difference between M55 and M22 may resemble the difference in integral CN band strength between M31 globular clusters and the galactic system. The colour-magnitude diagram of M55 shows the presence of a population of 56 blue-straggler stars that are more centrally concentrated than the red giant-branch stars.”

And viewing globular clusters like Messier 55 in a different wavelength of light other than optical reveals even more stunning details – like the vision of the XMM-Newton. As N.A. Webb (et al) said in their 2006 study:

“Using the new generation of X-ray observatories, we are now beginning to identify populations of close binaries in globular clusters, previously elusive in the optical domain because of the high stellar density. These binaries are thought to be, at least in part, responsible for delaying the inevitable core collapse of globular clusters and their identification is therefore essential in understanding the evolution of globular clusters, as well as being valuable in the study of the binaries themselves. Here, we present observations made with XMM-Newton of globular clusters, in which we have identified neutron star low mass X-ray binaries and their descendants (millisecond pulsars), cataclysmic variables and other types of binaries. We discuss not only the characteristics of these binaries, but also their formation and evolution in globular clusters and their use in tracing the dynamical history of these clusters.”

History of Observation:

M55 was originally discovered by Abbe Lacaille on June 16th, 1752, when he was observing in South Africa. In his notes, he wrote: “It resembles an obscure nucleus of a big comet.” Of course, our own comet hunter, Charles Messier, would search for a good many years before he recovered it to add to his own catalog. By July 24th, 1778, he found the object and recorded it as follows in his notes:

“A nebula which is a whitish spot, of about 6′ extension, its light is even and does not appear to contain any star. Its position has been determined from zeta Sagittarii, with the use of an intermediate star of 7th magnitude. This nebula has been discovered by M. l’Abbe de LaCaille, see Mem. Acad. 1755, p. 194. M. Messier has looked for it in vain on July 29, 1764, as reported in his memoir.”

Messier 55 in Sagittarius. Credit: Hewholooks/Wikipedia Commons

Johann Elert Bode, Dunlop and Caroline Herschel would follow, but it would be Sir William Herschel who would be first to glimpse the resolvability of this great globular cluster. In his private notes he writes:

“A rich cluster of very compressed stars, irregularly round, about 8 minutes long. By the observation of the small 20 feet telescope, which could reach stars 38.99 times as far as the eye, the profundity of this cluster cannot be much less than of the 467th order: I have taken it to be of the 400th order.”

Locating Messier 55:

M55 is by no means easy to find. One of the best ways to locate it is to begin at Theta 1 and Theta 2 Sagittarius, where you’ll find it approximately two finger widths northwest of this pair approximately four degrees. Both Thetas are on the dim side for the unaided eye – about magnitude 4 and 5 respectively, but you’ll recognize them when you find two stars separated by less than half a degree and oriented north/south.

For average binoculars, this will put M55 about a binocular field away to the northwest. For average image correct finderscopes, place the Thetas in the 8:00 position at the edge of the finderscope field and go to the eyepiece with the lowest possible magnification to locate it.

Messier 55 location. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

Although it has a high visual brightness, M55 has low surface brightness so it isn’t suitable to urban or light polluted skies. With dark sky conditions, binoculars will see it as a round hazy patch – like a diffuse comet, while small telescopes can begin to resolve individual stars. Larger aperture telescopes will pick out the fine grain of low magnitude stars quite easily!

Enjoy your own resolvability of this great globular cluster!

And as always, here are the quick facts on this Messier Object:

Object Name: Messier 55
Alternative Designations: M55, NGC 6809
Object Type: Class XI Globular Cluster
Constellation: Sagittarius
Right Ascension: 19 : 40.0 (h:m)
Declination: -30 : 58 (deg:m)
Distance: 17.3 (kly)
Visual Brightness: 6.3 (mag)
Apparent Dimension: 19.0 (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:

Posted on by Tammy Plotner

Messier 54 – the NGC 6715 Globular Cluster

Hubble image of Messier 54, a globular cluster located in the Sagittarius Dwarf Galaxy. Credit: ESA/Hubble & NASA

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at globular cluster known as Messier 54!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of these objects so others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is the globular cluster known as Messier 54. Located in the direction of the Sagittarius constellation, this cluster was once thought to be part of the Milky Way, located about 50,000 light years from Earth, In recent decades, astronomers have come to realize that it is actually part of the Sagittarius Dwarf Galaxy, located some 87,000 light-years away.

What You Are Looking At:

Running away from us at a speed of 142 kilometers per second, this compact globe of stars could be as wide as 150 light years in diameter and as far away as 87,400 light years. Wait… Hold the press… Almost 90 thousand light years? Yeah. Messier 54 isn’t part of our own Milky Way Galaxy!

In 1994 astronomers made a rather shocking discovery… this tough to resolve globular was actually part of the Sagittarius Dwarf Elliptical Galaxy. As Michael H. Siegal (et al) said in their study:

“As part of the ACS Survey of Galactic Globular Clusters, we present new Hubble Space Telescope photometry of the massive globular cluster M54 (NGC 6715) and the superposed core of the tidally disrupted Sagittarius (Sgr) dSph galaxy. Our deep (F606W ~ 26.5), high-precision photometry yields an unprecedentedly detailed color-magnitude diagram showing the extended blue horizontal branch and multiple main sequences of the M54+Sgr system. Multiple turnoffs indicate the presence of at least two intermediate-aged star formation epochs with 4 and 6 Gyr ages and [Fe/H]=-0.4 to -0.6. We also clearly show, for the first time, a prominent, ~2.3 Gyr old Sgr population of near-solar abundance. A trace population of even younger (~0.1-0.8 Gyr old), more metal-rich ([Fe/H]~0.6) stars is also indicated. The Sgr age-metallicity relation is consistent with a closed-box model and multiple (4-5) star formation bursts over the entire life of the satellite, including the time since Sgr began disrupting.”

Inside its compact depths lurk at least 82 known variable stars – 55 of which are the RR Lyrae type. But astronomers using the Hubble Space telescope have have also discovered there are two semi-regular red variables with periods of 77 and 101 days. Kevin Charles Schlaufman and Kenneth John Mighell of the National Optical Astronomy Observatory explained in their study:

“Most of our candidate variable stars are found on the PC1 images of the cluster center – a region where no variables have been reported by previous ground-based studies of variables in M54. These observations cannot be done from the ground, even with AO as there are far too many stars per resolution element in ground-based observations.”

The globular cluster Messier 54. Credit: NASA

But what other kinds of unusual stars could be discovered inside such distant cosmic stellar evolutionary laboratory? Try a phenomena known as blue hook stars! As Alfred Rosenberg (et al) said in their study:

“We present BV photometry centered on the globular cluster M54 (NGC 6715). The color-magnitude diagram clearly shows a blue horizontal branch extending anomalously beyond the zero-age horizontal-branch theoretical models. These kinds of horizontal-branch stars (also called “blue hook” stars), which go beyond the lower limit of the envelope mass of canonical horizontal-branch hot stars, have so far been known to exist in only a few globular clusters: NGC 2808, Omega Centauri (NGC 5139), NGC 6273, and NGC 6388. Those clusters, like M54, are among the most luminous in our Galaxy, indicating a possible correlation between the existence of these types of horizontal-branch stars and the total mass of the cluster. A gap in the observed horizontal branch of M54 around Teff = 27,000 K could be interpreted within the late helium flash theoretical scenario, which is a possible explanation for the origin of blue hook stars.”

But with the stars packaged together so tightly, even more has been bound to occur inside of Messier 54. As Tim Adams (et al) indicated in their study:

“We investigate a means of explaining the apparent paucity of red giant stars within post-core-collapse globular clusters. We propose that collisions between the red giants and binary systems can lead to the destruction of some proportion of the red giant population, by either knocking out the core of the red giant or by forming a common envelope system which will lead to the dissipation of the red giant envelope. Treating the red giant as two point masses, one for the core and another for the envelope (with an appropriate force law to take account of the distribution of mass), and the components of the binary system also treated as point masses, we utilize a four-body code to calculate the time-scales on which the collisions will occur. We then perform a series of smooth particle hydrodynamics runs to examine the details of mass transfer within the system. In addition, we show that collisions between single stars and red giants lead to the formation of a common envelope system which will destroy the red giant star. We find that low-velocity collision between binary systems and red giants can lead to the destruction of up to 13 per cent of the red giant population. This could help to explain the colour gradients observed in PCC globular clusters. We also find that there is the possibility that binary systems formed through both sorts of collision could eventually come into contact perhaps producing a population of cataclysmic variables.”

Messier 54, as imaged by the VLT Survey Telescope at ESO’s Paranal Observatory in northern Chile. Credit: ESO

But the discoveries haven’t ended yet…. Because 2009 studies have revealed evidence for an intermediate mass black hole inside Messier 54 – the first known to have ever been discovered in a globular cluster.

“We report the detection of a stellar density cusp and a velocity dispersion increase in the center of the globular cluster M54, located at the center of the Sagittarius dwarf galaxy (Sgr). The central line-of-sight velocity dispersion is 20.2 ± 0.7 km s-1, decreasing to 16.4 ± 0.4 km s-1 at 2farcs5 (0.3 pc). Modeling the kinematics and surface density profiles as the sum of a King model and a point-mass yields a black hole mass of ~9400 M sun.” says R. Ibata (et al), “However, the observations can alternatively be explained if the cusp stars possess moderate radial anisotropy. A Jeans analysis of the Sgr nucleus reveals a strong tangential anisotropy, probably a relic from the formation of the system.”

History of Observation:

On July 24, 1778 when Charles Messier first laid eyes on this faint fuzzy, he had no clue that he was about to discover the very first extra-galactic globular cluster. In his notes he writes: “Very faint nebula, discovered in Sagittarius; its center is brilliant and it contains no star, seen with an achromatic telescope of 3.5 feet. Its position has been determined from Zeta Sagittarii, of 3rd magnitude.”

Years later Sir William Herschel would also study M54, and in his private notes he writes: “A round, resolvable nebula. Very bright in the middle and the brightness diminishing gradually, about 2 1/2′ or 3′ in diameter. 240 shews too pretty large stars in the faint part of the nebulosity, but I rather suppose them to have no connection with the nebula. I believe it to be no other than a miniature cluster of very compressed stars.”

Countless other observations would follow as the M54 became cataloged by other astronomers and each would in turn describe it only as having a much brighter core and some resolution around the edges. Have fun trying to crack this one!

Locating Messier 54:

M54 isn’t hard to find… Just skip down to Zeta Sagittarii, the southwestern-most star of Sagittarius “teapot” and hop a half degree south and a finger width (1.5 degrees) west. The problem is seeing it! In small optics, such as binoculars or a finder scope, it will appear almost stellar because of its small size. However, if you just look for what appears like a larger, dim star that won’t quite come into perfect focus, then you’ve found it.

In smaller telescopes, you’ll get no resolution on this class III globular cluster because it is so dense. Large aperture doesn’t fare much better either, with only some individual stars making their appearance at the outer perimeters. Because of magnitude and size, Messier 54 is better suited to dark sky conditions.

The location of Messier 54 in the Sagittarius 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 54
Alternative Designations: M54, NGC 6715
Object Type: Class III Extragalactic Globular Cluster
Constellation: Sagittarius
Right Ascension: 18 : 55.1 (h:m)
Declination: -30 : 29 (deg:m)
Distance: 87.4 (kly)
Visual Brightness: 7.6 (mag)
Apparent Dimension: 12.0 (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, M8 – The Lagoon 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:

Posted on by Tammy Plotner

Messier 52 – the NGC 7654 Open Star Cluster

The location of the Messier 52 open star cluster, located in the direction of the southern constellation Cassiopeia. Credit: Wikisky

Welcome back to Messier Monday! We continue our tribute to our dear friend, Tammy Plotner, by looking at the open star cluster of Messier 52. Enjoy!

In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. In time, he would come to compile a list of approximately 100 of these objects, with the purpose of making sure that astronomers did not mistake them for comets. However, this list – known as the Messier Catalog – would go on to serve a more important function.

One of these objects is Messier 52, an open star cluster that can seen in proximity to the northern constellation Cassiopeia. Located about 5000 light years from Earth, this star cluster is easily spotted in the night sky because of its association with Cassiopeia’s familiar W-shape. It can viewed with binocular and telescopes, and will appears as a hazy, nebulous patch of light.

Description:

Located roughly 5000 light years away, this 35 million year old cluster of stars has around 200 members – one of which is a very peculiar Of star. According to A.K. Pandy (et al), M52 is an interesting cluster in which to study star formation history. As they stated in their 2001 study:

“The colour magnitude diagrams show a large age spread in the ages. Star formation was biased towards relatively higher masses during the early phase of star formation whereas most of the low mass stars of the cluster were formed during the later phase. The star formation seems to have been a gradual process that proceeded sequentially in mass and terminated with the formation of most massive stars.”

The Messier 52 open star cluster. Credit: Wikisky

Indeed, M52 has been very studied for its star structure, including a search for variables. As S.L. Kim (et al), wrote in a 2000 study:

“We have performed a long-term project of CCD photometry of open clusters. Its primary goal is to search for variable stars, in particular short-period (less than a few days) pulsating stars such as Delta Sct, Gamma Dor, and slowly pulsating B-type stars (SPBs). These pulsating stars are recognized as important objects in studying stellar structure and testing evolution theory of intermediate-mass main sequence stars. Thus these clusters are ideal targets to investigate whether Gamma Dor type variability occurs in old open clusters or not.”

And it’s not just the structure they’re looking at – but the time frame in which they formed. As Anil K. Pandey wrote in her 2001 study:

“The distribution of stars in NGC 7654 indicates that the star formation within the cluster is not coeval and has an age spread -50 Myr. We found that star formation took place sequentially in the sense that low mass stars formed first. The star formation history in NGC 7654 supports the conventional picture of star formation in cluster where ‘low mass stars’ form first and star formation continues over a long period of time. The star formation within the cluster terminates with the formation of most massive stars in the cluster.”

History of Observation:

M52 was an original discovery of Charles Messier, captured on the night of September 7th, 1774. As he wrote in his notes at the time:

“Cluster of very small stars, mingled with nebulosity, which can be seen only with an achromatic telescope. It was when he observed the Comet which appeared in this year that M. Messier saw this cluster, which was close to the comet on the 7th of September 1774; it is below the star d Cassiopeiae: that star was used to determine both the cluster of stars and the comet.”

Atlas Image mosaic of Messier 52, as part of the Two Micron All Sky Survey (2MASS). Credit: UMass/UPAC/Caltech/NASA/NSF

Sir William Herschel would also observe M52, but he would keep his notes private. As he wrote on August 29th, 1873:

“All resolved into innumerable small stars without any suspicion of nebulosity. 7 ft., 57. In the sweeper, 30, shews nebulosity, the stars being too obscure to be distinguished with its light tho’ considerable.” and again on December 23, 1805: “Review. Large 10 feet. This is a cluster of pretty condensed stars of different sizes. It is situated in a very rich part of the heavens and can hardly be called insulated, it may only be a very condensed part of the Milky Way which is here much divided and scattered. It is however so far drawn together with some accumulation that it may be called a cluster of the third order.”

Herschel’s son John would also add it to the General Catalog a few years later with less descriptive narrative, but it was Admiral Smyth who described M52’s beauty best when he said:

“An irregular cluster of stars between the head of Cepheus and his daughter’s throne; it lies north-west-by-west of Beta Cassiopeiae, and one third of the way towards Alpha Cephei. This object assumes somewhat of a triangular form, with an orange-tinted 8th-mag star at its vertex, giving it the resemblance of a bird with outspread wings. It is preceded by two stars of 7th and 8th magnitudes, and followed by another of similar brightness; and the field is one of singular beauty under a moderate magnifying power. While these were under examination, one of those bodies called falling stars passed through the outliers. This phenomenon was so unexpected and sudden as to preclude attention to it; but it appeared to be followed by a train of glittering and very minute spangles.”

May it glitter and spangle for you!

The location of Messier 52 in proximity to the constellation Cassiopeia. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

Locating Messier 52:

In the rich star cluster fields of Cassiopeia, M52 is distinctive for its size and brightness. It’s not hard to find! Begin by identifying the W-shape of Cassiopeia and focus on its two brightest stars – Alpha and Beta. Because this constellation is circumpolar, remembering to look at the side that has the brightest stars or the steepest angle, will help you remember how to find this great open cluster. Now, just draw a mental line between Alpha, the lower star, and Beta, the upper.

Extend that line into space about the same distance and aim your binoculars or finderscope there. In binoculars M52 will show clearly as a beginning to resolve star cloud and a hazy patch in a telescope finderscope. Even the smallest of telescopes can expect resolution from this multi-magnitude beauty and the more aperture you apply, the more stars you will see. M52 is well suited to urban or light polluted skies and stands up well to fairly moonlit conditions and hazy skies.

Object Name: Messier 52
Alternative Designations: M52, NGC 7654
Object Type: Open Galactic Star Cluster
Constellation: Cassiopeia
Right Ascension: 23 : 24.2 (h:m)
Declination: +61 : 35 (deg:m)
Distance: 5.0 (kly)
Visual Brightness: 7.3 (mag)
Apparent Dimension: 13.0 (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: