Hubble image of the Crab Nebula supernova remnant captured with the Wide Field and Planetary Camera 2. Credit: NASA, ESA, J. Hester and A. Loll (Arizona State University)
“The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars,” Carl Sagan famously said in his 1980 series Cosmos. “We are made of starstuff.”
And even today, observations with NASA’s airborne SOFIA observatory are supporting this statement. Measurements taken of the dusty leftovers from an ancient supernova located near the center our galaxy – aka SNR Sagittarius A East – show enough “starstuff” to build our entire planet many thousands of times over.
“Our observations reveal a particular cloud produced by a supernova explosion 10,000 years ago contains enough dust to make 7,000 Earths,” said research leader Ryan Lau of Cornell University in Ithaca, New York – the same school, by the way, where Carl Sagan taught astronomy and space science.
Composite image of SNR Sgr A East showing infrared SOFIA data outlined in white against X-ray and radio observations. (NASA/CXO/Herschel/VLA/Lau et al.)
While it’s long been known that supernovae expel enormous amounts of stellar material into space, it wasn’t understood if clouds of large-scale dust could withstand the immense shockwave forces of the explosion.
These observations, made with the joint NASA/DLR-developed Faint Object InfraRed Camera for the SOFIA Telescope (FORCAST) instrument, provide key “missing-link” evidence that dust clouds do in fact survive intact, spreading outward into interstellar space to seed the formation of new systems.
Interstellar dust plays a vital role in the evolution of galaxies and the formation of new stars and protoplanetary discs – the orbiting “pancakes” of material around stars from which planets (and eventually everything on them) form.
The findings may also answer the question of why young galaxies observed in the distant universe possess so much dust; it’s likely the result of frequent supernova explosions from massive early-generation stars.
“We have begun to contemplate our origins: starstuff pondering the stars; organized assemblages of ten billion billion billion atoms considering the evolution of atoms; tracing the long journey by which, here at least, consciousness arose.”
Nova Sagittarii 2015 No. 2 photographed this morning when it was easily visible to the naked eye at magnitude +4.4. The nova has been on the upswing since its discovered less than a week ago. Credit: Bob King
Great news about that new nova in Sagittarius. It’s still climbing in brightness and now ranks as the brightest nova seen from mid-northern latitudes in nearly two years. Even from the northern states, where Sagittarius hangs low in the sky before dawn, the “new star” was easy to spy this morning at magnitude +4.4.
While not as rare as hen’s teeth, novae aren’t common and those visible without optical aid even less so. The last naked eye nova seen from outside the tropics was V339 Del (Nova Delphini), which peaked at +4.3 in August 2013. The new kid on the block could soon outshine it if this happy trend continues.
This view shows the sky facing south-southeast shortly before the start of dawn in late March from the central U.S. The nova is centrally located within the Teapot. Source: Stellarium
Now bearing the official title of Nova Sagittarii 2015 No. 2, the nova was discovered on March 15 by amateur astronomer and nova hunter John Seach of Chatsworth Island, NSW, Australia. At the time it glowed at the naked eye limit of magnitude +6. Until this morning I wasn’t able to see it with the naked eye, but from a dark sky site, it’s there for the picking. So long as you know exactly where to look.
The chart and photo above will help guide you there. At the moment, the star’s about 15° high at dawn’s start, but it rises a little higher and becomes easier to see with each passing day. Find your sunrise time HERE and then subtract an hour and 45 minutes. That will bring you to the beginning of astronomical twilight, an ideal time to catch the nova at its highest in a dark sky.
Use this AAVSO chart to pinpoint the nova’s location and also to help you estimate its brightness. Numbers shown are star magnitudes with the decimal points omitted. Credit: AAVSO
To see it with the naked eye, identify the star with binoculars first and then aim your gaze there. I hope you’ll be as pleasantly surprised as I was to see it. To check on the nova’s ups and downs, drop by the American Association Variable Star Observers (AAVSO) list of recent observations.
Seeing the nova without optical aid took me back to the time before the telescope when a “new star” in the sky would have been met with great concern. Changes in the heavens in that pre-telescopic era were generally considered bad omens. They were also thought to occur either in Earth’s atmosphere or within the Solar System. The universe has grown by countless light years since then. Nowadays we sweat the small stuff – unseen asteroids – which were unknown in that time.
AAVSO light curve showing the nova’s brightening since discovery. Dates are along the bottom, magnitudes at left. If the trend continues, Nova Sgr #2 could outshine the 2013 nova in Delphinus very soon. Credit: AAVSO
Novae occur in binary star systems where a tiny but gravitationally powerful white dwarf star pulls gases from a close companion star. The material piles up in a thin layer on the dwarf’s hot surface, fuses and burns explosively to create the explosion we dub a nova. Spectra of the expanding debris envelope reveal the imprint of hydrogen gas and as well as ionized iron.
Artist’s view of a nova with an expanding cloud of debris surrounding the central fireball emitting red hydrogen-alpha light.
Shortly after discovery, the nova’s debris shell was expanding at the rate of ~1,740 miles per second (2,800 km/sec) or more than 6.2 million mph (10 million mph). It’s since slowed to about half that rate. Through a telescope the star glows pale yellow but watch for its color to deepen to yellow orange and even red. Right now, it’s still in the fireball phase, with the dwarf star hidden by an envelope of fiery hydrogen gas.
As novae evolve, they’ll often turn from white or yellow to red. Emission of deep red light from hydrogen atoms – called hydrogen alpha – gives them their warm, red color. Hydrogen, the most common element in stars, gets excited through intense radiation or collisions with atoms (heat) and re-emits a ruby red light when it returns to its rest state. Astronomers see the light as bright red emission line in the star’s spectrum. Spectra of the nova show additional emission lines of hydrogen beta or H-beta (blue light emitted by hydrogen) and iron.
There are actually several reasons why novae rouge up over time, according to former AAVSO director Arne Henden:
“Energy from the explosion gets absorbed by the surrounding material in a nova and re-emitted as H-alpha,” said Henden. Not only that but as the explosion expands over time, the same amount of energy is spread over a larger area.
“The temperature drops,” said Henden, “causing the fireball to cool and turn redder on its own.” As the eruption expands and cools, materials blasted into the surrounding space condense into a shell of soot that absorbs that reddens the nova much the same way dusty air reddens the Sun.
Nova Sagittarii’s current pale yellow color results from seeing a mix of light – blue from the explosion itself plus red from the expanding fireball. As for its distance from Earth, I haven’t heard, but given that the progenitor star was 15th magnitude or possibly fainter, we’re probably talking in the thousands of light years.
Wide view of the Sagittarius-Scorpius region with some of the brighter star clusters and nebulae labeled for binocular browsing. Credit: Bob King
In an earlier article on the nova’s discovery I mentioned taking a look at Saturn as long as you made the effort the get up early. Here’s a photo of the Sagittarius region you can use to help you further your dawn binocular explorations. The entire region is rich with star clusters and nebula, many of which were cataloged long ago by French astronomer Charles Messier, hence the “M” numbers.
Brightest star Sirius (lower center) rules the anthropocene night. Credit and copyright: Alan Dyer.
What’s the brightest star you can see in the sky tonight?
If you live below 83 degrees north latitude, the brightest star in the sky is Canis Alpha Majoris, or Sirius. Seriously, (bad pun intended) the -1st magnitude star is usually the fifth brightest natural object in the sky, and sits high to the south on February evenings… but has it always ruled the night? Continue reading “What is the Brightest Star in the Sky, Past and Future?”
A binary star system Credit: Michael Osadciw/University of Rochester
Astronomers have reported the discovery of a star that passed within the outer reaches of our Solar System just 70,000 years ago, when early humans were beginning to take a foothold here on Earth. The stellar flyby was likely close enough to have influenced the orbits of comets in the outer Oort Cloud, but Neandertals and Cro Magnons – our early ancestors – were not in danger. But now astronomers are ready to look for more stars like this one.
A comparison of the Solar System and its Oort Cloud. 70,000 years ago, Scholz’s Star and companion passed along the outer boundaries of our Solar System (Credit: NASA, Michael Osadciw/University of Rochester, Illustration-T.Reyes)
Lead author Eric Mamajek from the University of Rochester and collaborators report in The Closest Known Flyby Of A Star To The Solar System (published in Astrophysical Journal on February 12, 2015) that “the flyby of this system likely caused negligible impact on the flux of long-period comets, the recent discovery of this binary highlights that dynamically important Oort Cloud perturbers may be lurking among nearby stars.”
The star, named Scholz’s star, was just 8/10ths of a light year at closest approach to the Sun. In comparison, the nearest known star to the Sun is Proxima Centauri at 4.2 light years.
While the internet has been rife with threads and accusations of a Nemesis star that is approaching the inner Solar System and is somehow being “hidden” by NASA, this small red dwarf star with a companion represents the real thing.
In 1984, the paleontologists David Raup and Jack Sepkoski postulated that a dim dwarf star, now widely known on the internet as the Nemesis Star, was in a very long period Solar orbit. The elliptical orbit brought the proposed star into the inner Solar System every 26 million years, causing a rain of comets and mass extinctions on that time period. By no coincidence, because of the sheer numbers of red dwarfs throughout the galaxy, Scholz’s star nearly fits such a scenario. Nemesis was proposed to be in a orbit extending 95,000 A.U. compared to Scholz’s nearest flyby distance of 50,000 A.U. Recent studies of impact rates on Earth, the Moon and Mars have discounted the existence of a Nemesis star (see New Impact Rate Count Lays Nemesis Theory to Rest, Universe Today, 8/1/2011)
But Scholz’s star — a real-life Oort Cloud perturber — was a small red dwarf star star with a M9 spectral classification. M-class stars are the most common star in our galaxy and likely the whole Universe, as 75% of all stars are of this type. Scholz’s is just 15% of the mass of our Sun. Furthermore, Scholz’s is a binary star system with the secondary being a brown dwarf of class T5. Brown Dwarfs are believed to be plentiful in the Universe but due to their very low intrinsic brightness, they are very difficult to discover … except, as in this case, as companions to brighter stars.
The astronomers reported that their survey of new astrometric data of nearby stars identified Scholz’s as an object of interest. The star’s transverse velocity was very low, that is, the stars sideways motion. Additionally, they recognized that its radial velocity – motion towards or away from us, was quite high. For Scholz’s, the star was speeding directly away from our Solar System. How close could Scholz’s star have been to our system in the past? They needed more accurate data.
The collaborators turned to two large telescopes in the southern hemisphere. Spectrographs were employed on the Southern African Large Telescope (SALT) in South Africa and the Magellan telescope at Las Campanas Observatory, Chile. With more accurate trangental and radial velocities, the researchers were able to calculate the trajectory, accounting for the Sun’s and Scholz’s motion around the Milky Way galaxy.
Scholz’s star is an active star and the researchers added that while it was nearby, it shined at a dimly of about 11th magnitude but eruptions and flares on its surface could have raised its brightness to visible levels and could have been seen as a “new” star by primitive humans of the time.
The relative sizes of the inner Solar System, Kuiper Belt and the Oort Cloud. (Credit: NASA, William Crochot)
At present, Scholz’s star is 20 light years away, one of the 70 closest stars to our Solar System. However, the astronomers calculated, with a 98% certainty, that Scholz’s passed within 0.5 light years, approximately 50,000 Astronomical Units (A.U.) of the Sun.
An A.U. is the mean distance from the Earth to the Sun and 50,000 is an important mile marker in our Solar System. It is the outer reaches of the Oort Cloud where billions of comets reside in cold storage, in orbits that take hundreds of thousands of years to circle the Sun.
With this first extraordinary close encounter discovered, the collaborators of this paper as well as other researchers are planning new searches for “Nemesis” type stars. The Large Synoptic Survey Telescope (LSST) and other telescopes within the next decade will bring an incredible array of data sets that will uncover many more red dwarf, brown dwarf and possibly orphan planets roaming in nearby space. Some of these could likewise be traced to past or future near misses to the Sun and Earth system.
Tauris argues that a lopsided supernova explosion may be the source of certain hypervelocity stars (image credit: IsiacDaGraca).
Hypervelocity stars have been observed traversing the Galaxy at extreme velocities (700 km/s), but the mechanisms that give rise to such phenomena are still debated. Astronomer Thomas M. Tauris argues that lopsided supernova explosions can eject lower-mass Solar stars from the Galaxy at speeds up to 1280 km/s. “[This mechanism] can account for the majority (if not all) of the detected G/K-dwarf hypervelocity candidates,” he said.
Several mechanisms have been proposed as the source for hypervelocity stars, and the hypotheses can vary as a function of stellar type. A simplified summary of the hypothesis Tauris favors begins with a higher-mass star in a tight binary system, which finally undergoes a core-collapse supernova explosion. The close proximity of the stars in the system partly ensures that the orbital velocities are exceedingly large. The binary system is disrupted by the supernova explosion, which is lopsided (asymmetric) and imparts a significant kick to the emerging neutron star. The remnants of supernovae with massive progenitors are neutron stars or potentially a more exotic object (i.e., black hole).
Conversely, Tauris noted that the aforementioned binary origin cannot easily explain the observed velocities of all higher-mass hypervelocity stars, namely the B-stars, which are often linked to an ejection mechanism from a binary interaction with the supermassive black hole at the Milky Way’s center. Others have proposed that interactions between multiple stars near the centers of star clusters can give rise to certain hypervelocity candidates.
There are several potential compact objects (neutron stars) which feature extreme velocities, such as B2011+38, B2224+65, IGR J11014-6103, and B1508+55, with the latter possibly exhibiting a velocity of 1100 km/s. However, Tauris ends by noting that, “a firm identification of a hypervelocity star being ejected from a binary via a supernova is still missing, although a candidate exists (HD 271791) that’s being debated.”
Be it atoms, stars or snowflakes from the latest nor’easter pounding the New England seaboard, anything worth studying involves movement. And as skies and snowbound roads clear, this Wednesday and Thursday evening will give us a reason to brave the January cold, as the waxing gibbous Moon pierces the Hyades star cluster to graze past the bright star Aldebaran.
During Thursday night’s passage, the Moon will be 78% illuminated. In a sort ‘cosmos mimics controversy’ irony, the gibbous Moon is doing its best to mimic a sky bound ‘deflategate’ football just in time for Superbowl XLIX this weekend.
The motion of the Moon this week across the Hyades. Credit: Stellarium.
But the January 29th event also marks the first occultation of Aldebaran for 2015.
Fun fact: At magnitude +0.8, Aldebaran is the only star brighter than +1st magnitude north of the celestial equator that the Moon can currently occult. Regulus, the runner up, shines at magnitude +1.4. Two other second magnitude stars — Antares and Spica — lie along the Moon’s path on occasion, and up until the 2nd century BC, it was possible for the Moon to occult Pollux in the constellation Gemini as well.
There are 13 occultations of Aldebaran in 2015, and the Moon occults the star 49 times overall until the last event in the current cycle on September 3rd, 2018. Aldebaran is also occulted by the Moon more often in the current 2010-2020 decade than any other bright star. You can even spy Aldebaran near the daytime Moon with binoculars, as we did back in 1996 from North Pole, Alaska.
Maps for the 13 occultations of Aldebaran by the Moon in 2015, click to enlarge. solid lines denote regions were the occultation occurs under dark skies. Credit: Occult 4.0.
Of course, the January 29th event is an occultation only for the high Arctic, with only a scattering of villages and distant early warning stations along the northern Nunavut coast welcoming the sequence of 2015 occultations of the bright star.
The rest of us will see a close photogenic pass, as the Moon makes an end run through the Hyades star cluster every 27.3 day sidereal lunar month in 2015. The Moon will thus occult several members of the Hyades on each pass. Our best bet for North America is the occultation of Aldebaran on November 26th, though the Moon will be just 13 hours past Full.
The occultation of 68 Tauri (a member of the Hyades) for January 29th. Credit: Occult 4.0.
Why doesn’t the path of the Moon just stay put with respect to the sky? Because the orbit of our Moon is fixed at an inclination of 5.1 degrees not with respect to our equator, but to the plane of the ecliptic. This means that the Moon’s orbit is in motion as well, and can wander anywhere from declination 28.6 degrees north to south as it cycles from a shallow to steep path every 18.6 years. We’re actually in a shallow year in 2015 (known as a minor lunar standstill) after which the apparent path of the Moon through the sky begins to widen again until April 2025.
An occultation is celestial motion that you can see in real time as a star or planet is photobomb’d by the onrushing Moon like a January snowplow… but those background stars are in motion as well.
The Hyades themselves — along with our own solar system — are moving around the galactic center. The nearest open cluster to us at 153 light years distant, the Hyades provided a unique object of study for 19th century astronomers. Astronomer Lewis Boss of the Dudley observatory spent several decades studying the proper motion — the apparent motion that a star seems to be moving across the sky from our solar system-bound perspective, measured in arc seconds — of the Hyades, and found the entire group was converging on a point in the constellation Orion near 6 hours 7’ right ascension and +7 degrees declination.
The imaginary convergent point of the Hyades in the night sky. Credit: Starry Night Education software.
Of course, this motion is relative and demonstrates a changing perspective, as the Hyades recedes from our solar system like a defensive line rushing to sack a quarterback.
OK, enough with the sports similes. The Hyades are so close that the actual Hyades Stream — often referred to as the Hyades Moving Group — is actually strewn across the constellations Orion, Taurus and Aries and more.
Some stars, such as 20 Arietis in the adjacent constellation Aries and Iota Horologii in the southern hemisphere may actually members as well. There’s always a bit of ongoing controversy when it comes to actual moving group membership, which is usually pegged by determining proper motion, coupled with the age and metallicity of prospective stars. Growing up in the Milky Way galaxy, our Sun was once a member of some unnamed ancient open cluster that has since long dispersed, like the Hyades are in the process of doing now.
The asterism of the Hyades and the ‘eye of the Bull.’ Photo by author.
The Hyades contains hundreds of stars and ironically, Aldebaran is not a member of the cluster, but is merely 65 light years away from us in the foreground. The V-shaped asterism of the Hyades gives the Head of Taurus the Bull its distinctive shape. The Hyades are named after the rain nymph daughters of Atlas from Greek mythology, whose half daughters the Pleiades also adorn the nearby sky.
And as an added bonus, don’t miss comet C/2014 Q2 Lovejoy crossing the constellation Triangulum, also nearby. Q2 Lovejoy reaches perihelion this week on January 30th, and although it’s completing with the evening Moon, it’s still holding out at a respectable magnitude +4.5.
Comet Q2 Lovejoy skirts by the Hyades and the Pleiades. Credit and Copyright: John Chumack.
All reasons to get out these chilly January evenings and ponder a hurried universe continually in motion, both fast and slow.
This artist’s impression shows an eclipsing binary star system. Credit: ESO/L. Calçada.
Update: It’s off. This past weekend, the AAVSO issued Special Notice #395 calling off the campaign to observe Alpha Comae Berenices this month due to “position measurements published a century ago (which) contained errors that affected the predictions for the time of eclipse…”
And the mystery of Alpha Comae Berenices continues. Oh well. Such is the wiles and whims of the universe, and the exciting field of variable star observing!
A truly fascinating event may be in the offing this month.
Picture two distant burning embers (candles, light bulbs, LEDs, what have you) circling each other in the distance. From our far-flung vantage point, the two points of light are too faint to resolve individually, but as they pass in front of each other, a telltale dip in combined brightness occurs as one blocks out the other.
Welcome to the fascinating world of eclipsing binary stars. This week, we’d like to turn our attention towards a special star in the constellation of Coma Berenices which may — or may not — put on such a dimming act later this month.
An Alpha Comae Berenices (Diadem) finder chart, with comparison stars and magnitudes, decimals omitted. Credit: Starry Night Education Software.
The brightest star in the constellation Coma Berenices, Alpha (sometimes referred to as Diadem, or the ‘crown’ of Queen Berenice) shines at an apparent magnitude of +4.3. Located 63 light years distant, the system consists of two +5th magnitude F-type stars each about 3 times more luminous than our Sun locked in a 26 year orbital embrace. The physical separation of the pair is about 10 astronomical units: place Alpha Comae Berenices in our solar system, and the pair would fit nicely between the Sun and Saturn.
The orbital plane of the pair is inclined nearly along our line of sight as seen from the Earth, and it’s long been thought that catching a grazing or central eclipse of the pair might just be possible. No eclipse was recorded last time ‘round back in February 1989, but times have changed lots in observational astronomy. Today, there are enough backyard observers armed with dedicated observatories and rigs that’d be the envy of a small university that documenting such an eclipse might just be possible. In fact, a central eclipse might just dim the star by 0.8 magnitudes, and should be noticeable to the naked eye.
The binary nature of Alpha Comae Berenices was first noted by F. G. W. Struve in 1827, and the split is a challenging one during the best of years with a maximum angular separation of just 0.7 arc seconds. The pair also has a third faint +10th magnitude companion located about 89 arc seconds away.
A simplified diagram depicting an eclipsing binary event along our line of sight. Created by the author.
The American Association of Variable Star Observers (AAVSO) has an Alert Notice calling for sky watchers worldwide to monitor the star. We also understand the orbit of Alpha Comae Berenices much better in 2015 than back in 1989, and the suspected eclipse should occur somewhere between January 22nd and January 28th and may last anywhere from 28 to 45 hours. This lingering ambiguity means that having a dedicated team of observers worldwide may well be key to nabbing this eclipse.
Alpha Comae Berenices rising. Photo by the author.
The Navy Precision Optical Interferometer (NPOI) has already begun refining measurements of the brightness of the star last month, and professional facilities, to include the Fairborn Observatory atop Mt Hopkins in Arizona and the CHARA (the Center for High Angular Resolution Astronomy) Array at Mount Wilson Observatory in southern California will also be monitoring the event.
Sky and Telescope magazine also has an excellent article in their January 2015 issue on the prospects for catching this eclipse.
Looking eastward past local midnight. Credit: Stellarium.
In late January, the constellation of Coma Berenices rises high to the northeast just after local midnight. It’s worth noting that, if the eclipsing binary nature of Alpha Comae Berenices is confirmed, it would be the longest period known, beating out 14.6 year Gamma Persei discovered in 1990 by more than a decade. A system with as wide a separation as Alpha Comae Berenices would have about a 1 in 1,200 chance in eclipsing along our line of sight due to random chance.
Note: Epsilon Aurigae does have a comparable 27 year period involving a debris disk surrounding its host star. Thanks to sharp-eyed reader Dr. John Barentine for pointing this out!
Of course, the universe does provide us with lots of near misses, allowing for an ‘occasional Diadem’ to indeed occur. Most famous eclipsing variables, such as Algol or Beta Lyrae have periods measured over the span of days or hours. Incidentally, these also make great ‘practice stars’ to test your skills as a visual athlete leading up to the big event next week. A skilled visual observer can note a change as slight as a 0.1 of a magnitude, and it’s a good idea to begin familiarizing yourself with the environs of the star now. The Coma Cluster of galaxies, the globular cluster M53, and the galactic plane crossing intruder Arcturus all lie nearby.
The Coma Cluster as seen by Spitzer Space Telescope and the Sloan Digital Sky Survey. Credit: NASA/Spitzer.
Why study eclipsing binaries? Well, said fleeting mutual events when coupled with spectroscopic measurements and determinations of parallax can tell us a good deal about the astrophysical nature of the stars involved. Eclipsing binary stars have even been used to back up standard candle measurements over extragalactic distances. And of course, orbiting observatories such as Kepler and TESS (to be launched in 2017) look for transiting exoplanets using virtually the same method.
Have a scope+DSLR? Then you can make refined measurements of eclipsing variable stars. Credit: Brad Timerson/IOTA.
But beyond its practical application, we just think that it’s plain cool that you can actually see something out beyond our solar system changing in the span of just a few days or hours.
Observers also still carry out visual observations of variable stars, just like those pipe-smoking, pocket watch carrying astronomers of yore. This involves merely comparing the target star to nearby stars of the same brightness. If you have a DSLR or a CCD rig plus a telescope, the AAVSO also has instructions for how to monitor a star’s brightness as well. No pocket watch required.
A homemade ‘card interferometer’ used to measure the separation of close double stars. Photo by author.
Unless, of course, you want to carry a pocket watch just for good luck. Don’t let the cold January winters keep you from joining the hunt. Let’s make some astrophysical history!
The dark nebula LDN 483 imaged by ESO's La Silla Observatory in Chile (ESO)
What may appear at first glance to be an eerie, empty void in an otherwise star-filled scene is really a cloud of cold, dark dust and molecular gas, so dense and opaque that it obscures the distant stars that lie beyond it from our point of view.
Similar to the more well-known Barnard 68, “dark nebula” LDN 483 is seen above in an image taken by the MPG/ESO 2.2-meter telescope’s Wide Field Imager at the La Silla Observatory in Chile.
While it might seem like a cosmic no-man’s-land, no stars were harmed in the making of this image – on the contrary, dark nebulae like LDN 483 are veritable maternity wards for stars. As their cold gas and dust contracts and collapses new stars form inside them, remaining cool until they build up enough density and gravity to ignite fusion within their cores. Then, shining brightly, the young stars will gradually blast away the remaining material with their outpouring wind and radiation to reveal themselves to the galaxy.
The process may take several million years, but that’s just a brief flash in the age of the Universe. Until then, gestating stars within LDN 483 and many other clouds like it remain dim and hidden but keep growing strong.
Wide-field view of the LDN 483 region. (Credit: ESO and Digitized Sky Survey 2)
To a distant observer, our own Milky Way and the Andromeda galaxy would probably look very similar. Although Andromeda is longer, more massive, and more luminous than the Milky Way, both galaxies are vast spirals composed of hundreds of millions of stars. But new research presented at this week’s AAS conference in Seattle suggests that there are other differences as well – namely, in the movement and behavior of certain stellar age groups. This observation is the first of its kind, and raises new questions about the factors that contribute to the formation of spiral galaxies like our own.
Armed with data from both the Hubble Space Telescope and the Keck Observatory in Hawaii, a group of astronomers from UC Santa Cruz resolved 10,000 tiny points of light in the Andromeda galaxy into individual stars and used their spectra to calculate the stars’ ages and velocities – a feat never before accomplished for a galaxy outside of our own.
Led by Puragra Guhathakurta, a professor of astrophysics, and Claire Dorman, a graduate student, the researchers found that in Andromeda, the behavior of older stars is surprisingly more frazzled than that of their younger counterparts; that is, they have a much wider range of velocities around the galactic center. Meanwhile, in the Milky Way, stars of all ages seem to coexist far more peacefully, moving along at the same speed in a consistent, ordered pack.
The astronomers believe that this asymmetry causes Andromeda to look more distinct from our own galaxy than previously thought. “If you could look at [Andromeda’s] disk edge on, the stars in the well-ordered, coherent population would lie in a very thin plane, whereas the stars in the disordered population would form a much puffier layer,” said Dorman.
What could account for such disorderly conduct among Andromeda’s older generation? It is possible that these more mature stars could have been disturbed long ago, during episodes of the kind of “galactic cannibalism” that is thought to go on among most spiral galaxies. Indeed, trails of stars in its outer halo suggest that Andromeda has collided with and consumed a number of smaller galaxies over the course of its lifetime; however, these effects cannot completely account for the jumbled flow of Andromeda’s most elderly stars.
A few examples of galactic cannibalism. NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University), K. Noll (STScI), and J. Westphal (Caltech)
Astronomers believe that a second explanation could fill in the blanks – one that owes to events occurring far earlier in history, during the birth of the galaxy itself. After all, if Andromeda originated from a lumpy, irregular gas cloud, its oldest stars would naturally appear fairly disordered. Over time, the parent gas would have settled down, giving rise to ever more organized generations of stars.
Guhathakurta, Dorman, and the rest of the team hope that their work will encourage other scientists to create simulations that will better constrain these possibilities. To them, understanding Andromeda is a vital key to learning more about our own galaxy. Guhathakurta explained, “In the Andromeda galaxy we have the unique combination of a global yet detailed view of a galaxy similar to our own. We have lots of detail in our own Milky Way, but not the global, external perspective.”
Now, thanks to this new research, scientists can cite our own galaxy’s comparative orderliness as strong evidence that we live in a quieter, less cannibalistic neighborhood than most other spiral galaxies in the Universe. “Even the most well ordered Andromeda stars are not as well ordered as the stars in the Milky Way’s disk,” said Dorman.
At least until 4 billion years from now, when the Milky Way and Andromeda collide.
We may as well enjoy the A+ for conduct while we can.
A colorful photo of the "Tulip Nebula" taken by Julian Hancock.
We often publish photos from professional observatories, but it’s important to note that amateurs can also do a great job taking pictures of the sky with modest equipment and photo processing software.
On Universe Today’s Flickr pool, we’re proud to showcase the work of all the fans of the cosmos. Included here are some of the best shots of galaxies and nebulas that we’ve seen uploaded to the site in recent days.
The Milky Way shines over Termas de Chillán in this photo taken by “Miss Andrea” on Flickr.The center of the Heart Nebula captured by David Wills on Flickr.Simeis 147, the “Spaghetti Nebula”, shines in hydrogen alpha in this image captured by Rick Stevenson on Flickr.The Tarantula Nebula imaged in Ha, OIII and SII by Alan Tough on Flickr.
