This Large Binocular Telescope image below of the Whirlpool Galaxy, otherwise known as M51, is part of a new galaxy survey by Ohio State University, where astronomers are searching for signs that stars are about to go supernova. The insets show one particular binary star system before (left) and after (right) one of its stars went supernova. Image by Dorota Szczygiel, courtesy of Ohio State University.
[/caption] This past year has given both backyard and professional astronomers a rare treat – a very visible supernova event. Hosted in the Whirlpool Galaxy (M51), these stellar death throes may have been clued to us by a rather ordinary binary star system. In a recent study done by researchers at Ohio State University, a galaxy survey may have captured evidence of a “stellar signal” just before it went supernova!
Employing the Large Binocular Telescope located in Arizona, the OSU team was undertaking a survey of 25 galaxies for stars that changed their magnitude in usual ways. Their goal was to find a star just before it ended its life – a three-year undertaking. As luck would have it, a binary star system located in M51 produced just the results they were looking for. One star dropped amplitude just a short period of time before the other exploded. While the probability factor of them getting the exact star might be slim, chances are still good they caught its brighter partner. Despite that, principal investigator Christopher Kochanek, professor of astronomy at Ohio State and the Ohio Eminent Scholar in Observational Cosmology, remains optimistic as their results prove a theory.
“Our underlying goal is to look for any kind of signature behavior that will enable us to identify stars before they explode,” he said. “It’s a speculative goal at this point, but at least now we know that it’s possible.”
“Maybe stars give off a clear signal of impending doom, maybe they don’t,” said study co-author Krzystof Stanek, professor of astronomy at Ohio State, “But we’ll learn something new about dying stars no matter the outcome.”
Postdoctoral researcher Dorota Szczygiel, the leader of the supernova study tells us why the galaxy survey remains paramount.
“The odds are extremely low that we would just happen to be observing a star for several years before it went supernova. We would have to be extremely lucky,” she said. “With this galaxy survey, we’re making our own luck. We’re studying all the variable stars in 25 galaxies, so that when one of them happens go supernova, we’ve already compiled data on it.”
On May 31, 2011, the whole astronomy world was abuzz when SN2011dh gave both amateurs and professionals a real thrill as an easily observable event. As luck would have it, it was a binary star system being studied by the OSU team, and consisted of both a blue and red star. At this point, the astronomers surmise the red star was the one that dimmed significantly over the three-year period while the blue one blew its top. When reviewing the LBT data, the Ohio team found that when compared with Hubble images, the red star dimmed at about 10% over the final three-year period at an estimated 3% per previous years. As a curiosity, the researchers surmise the red star may have actually survived the supernova event.
“After the light from the explosion fades away, we should be able to see the companion that did not explode,” Szczygiel said.
As the team continues to collect valuable information, they estimate they could also detect another candidate set of stars at a rate of about one per year. There is also a strong possibility these detections could act as a type of test bed to predict future supernova events… looking for signals of impending doom. However, according to the news release, the Sun won’t be one to bother with.
“There’ll be no supernova for the Sun – it’ll just fizzle out,” Kochanek said. “But that’s okay – you don’t want to live around an exciting star.”
Galaxy Cluster MACS J0329.6-0211 lenses several background galaxies including a distant dwarf galaxy. CREDIT: A. Zitrin, et al.
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Gravitational lensing is a powerful tool for astronomers that allows them to explore distant galaxies in far more detail than would otherwise be allowed. Without this technique, galaxies at the edge of the visible universe are little more than tiny blobs of light, but when magnified dozens of times by foreground clusters, astronomers are able to explore the internal structural properties more directly.
Recently, astronomers at the University of Heidelberg discovered a gravitational lensed galaxy that ranked among the most distant ever seen. Although there’s a few that beat this one out in distance, this one is remarkable for being a rare quadruple lens.
The images for this remarkable discovery were taken using the Hubble Space Telescope in August and October of this year, using a total of 16 different colored filters as well as additional data from the Spitzer infrared telescope. The foreground cluster, MACS J0329.6-0211, is some 4.6 billion light years distant. In the above image, the background galaxy has been split into four images, labelled by the red ovals and marked as 1.1 – 1.4. They are enlarged in the upper right.
Assuming that the mass of the foreground cluster is concentrated around the galaxies that were visible, the team attempted to reverse the effects the cluster would have on the distant galaxy, which would reverse the distortions. The restored image, also corrected for redshift, is shown in the lower box in the upper right corner.
After correcting for these distortions, the team estimated that the total mass of the distant galaxy is only a few billion times the mass of the Sun. In comparison, the Large Magellanic Cloud, a dwarf satellite to our own galaxy, is roughly ten billion solar masses. The overall size of the galaxy was determined to be small as well. These conclusions fit well with expectations of galaxies in the early universe which predict that the large galaxies in today’s universe were built from the combination of many smaller galaxies like this one in the distant past.
The galaxy also conforms to expectations regarding the amount of heavy elements which is significantly lower than stars like the Sun. This lack of heavy elements means that there should be little in the way of dust grains. Such dust tends to be a strong block of shorter wavelengths of light such as ultraviolet and blue. Its absence helps give the galaxy its blue tint.
Star formation is also high in the galaxy. The rate at which they predict new stars are being born is somewhat higher than in other galaxies discovered around the same distance, but the presence of brighter clumps in the restored image suggest the galaxy may be undergoing some interactions, driving the formation of new stars.
NGC7600 is an elliptical galaxy and is around 50 Mpc in distance. This image shows an interleaved system of shells that are described in this Astronomical Journal Letters here. These types of structures around elliptical galaxies were first revealed by Malin & Carter in 1980. This deep image of NGC7600 shows faint features not previously seen. Credit: Ken Crawford
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As a professional astronomy journalist, I read a lot of science papers. It hasn’t been all that long ago that I remember studying about galaxy groups – with the topic of dark matter and dwarf galaxies in particular. Imagine my surprise when I learn that two of my friends, who are highly noted astrophotographers, have been hard at work doing some deep blue science. If you aren’t familiar with the achievements of Ken Crawford and R. Jay Gabany, you soon will be. Step inside here and let us tell you why “it matters”…
According to Ken’s reports, Cold Dark Matter (or CDM) is a theory that most of the material in the Universe cannot be seen (dark) and that it moves very slowly (cold). It is the leading theory that helps explain the formation of galaxies, galaxy groups and even the current known structure of the universe. One of the problems with the theory is that it predicts large amounts of small satellite galaxies called dwarf galaxies. These small galaxies are about 1000th the mass of our Milky Way but the problem is, these are not observed. If this theory is correct, then where are all of the huge amounts of dwarf galaxies that should be there?
Enter professional star stream hunter, Dr. David Martinez-Delgado. David is the principal investigator of the Stellar Tidal Stream Survey at the Max-Planck Institute in Heidelberg, Germany. He believes the reason we do not see large amounts of dwarf galaxies is because they are absorbed (eaten) by larger galaxies as part of the galaxy formation. If this is correct, then we should find remnants of these mergers in observations. These remnants would show up as trails of dwarf galaxy debris made up mostly of stars. These debris trails are called star streams.
“The main aim of our project is to check if the frequency of streams around Milky Way-like galaxies in the local universe is consistent with CDM models similar to that of the movie.” clarifies Dr. Martinez-Delgado. “However, the tidal destruction of galaxies is not enough to solve the missing satellite problem of the CDM cosmology. So far, the best given explanation is that some dark matter halos are not able to form stars inside, that is, our Galaxy would surround by a few hundreds of pure dark matter satellites.”
Enter the star stream hunters professional team. The international team of professional astronomers led by Dr. David Martinez-Delgado has identified enormous star streams on the periphery of nearby spiral galaxies. With deep images he showed the process of galactic cannibalism believed to be occurring between the Milky Way and the Sagittarius dwarf galaxy. This is in our own back yard! Part of the work is using computer modeling to show how larger galaxies merge and absorb the smaller ones.
This image has been inverted and contrast enhanced to help display the faint shell features and debris fragments. The farthest fragment is 140 kpc in projection from the center of the galaxy. Credit: Ken Crawford“Our observational approach is based on deep color-magnitude diagrams that provide accurate distances, surface brightness, and the properties of stellar population of the studied region of this tidal stream.” says Dr. Martinez-Delgado (et al). “These detections are also strong observational evidence that the tidal stream discovered by the Sloan Digitized Sky Survey is tidally stripped material from the Sagittarius dwarf and support the idea that the tidal stream completely enwraps the Milky Way in an almost polar orbit. We also confirm these detections by running numerical simulations of the Sagittarius dwarf plus the Milky Way. This model reproduces the present position and velocity of the Sagittarius main body and presents a long tidal stream formed by tidal interaction with the Milky Way potential.”
Enter the team of amateurs led by R. Jay Gabany. David recruited a small group of amateur astrophotographers to help search for and detect these stellar fossils and their cosmic dance around nearby galaxies, thus showing why there are so few dwarf galaxies to be found.
“Our observations have led to the discovery of six previously undetected, gigantic, stellar structures in the halos of several galaxies that are likely associated with debris from satellites that were tidally disrupted far in the distant past. In addition, we also confirmed several enormous stellar structures previously reported in the literature, but never before interpreted as being tidal streams.” says the team. “Our collection of galaxies presents an assortment of tidal phenomena exhibiting strikingly diverse morphological characteristics. In addition to identifying great circular features that resemble the Sagittarius stream surrounding the Milky Way, our observations have uncovered enormous structures that extend tens of kiloparsecs into the halos of their host’s central spiral. We have also found remote shells, giant clouds of debris within galactic halos, jet-like features emerging from galactic disks and large-scale, diffuse structures that are almost certainly related to the remnants of ancient, already thoroughly disrupted satellites. Together with these remains of possibly long defunct companions, our survey also captured surviving satellites caught in the act of tidal disruption. Some of these display long tails extending away from the progenitor satellite very similar to the predictions forecasted by cosmological simulations.”
The .5 meter Ritchey-Chretien Telescope of the Blackbird Observatory is situated at 7300 ft.(2225 meters) elevation under spectacularly clear and dark skies in the south central Sacramento Mountains of New Mexico, near Mayhill. Photo credit: R. Wodaski
Can you imagine how exciting it is to be part of deep blue science? It is one thing to be a good astrophotographer – even to be an exceptional astrophotographer – but to have your images and processing to be of such high quality as to be contributory to true astronomical research would be an incredible honor. Just ask Ken Crawford…
“Several years ago I was asked to become part of this team and have made several contributions to the survey. I am excited to announce that my latest contribution has resulted in a professional letter that has been recently accepted by the Astronomical Journal.” comments Ken. “There are a few things that make this very special. One, is that Carlos Frenk the director of the Institute for Computational Cosmology at Durham University (UK) and his team found that my image of galaxy NGC7600 was similar enough to help validate their computer model (simulation) of how larger galaxies form by absorbing satellite dwarf galaxies and why we do not see large number of dwarf galaxies today.”
Dr. Carlos Frenk has been featured on several television shows on the Science and Discovery channels, to name a few, to explain and show some of these amazing simulations. He is the director of the Institute for Computational Cosmology at Durham University (UK), was one of the winners of the 2011 Cosmology Prize of The Peter and Patricia Gruber Foundation.
“The cold dark matter model has become the leading theoretical picture for the formation of structure in the Universe. This model, together with the theory of cosmic inflation, makes a clear prediction for the initial conditions for structure formation and predicts that structures grow hierarchically through gravitational instability.” says Frenk (et al). “Testing this model requires that the precise measurements delivered by galaxy surveys can be compared to robust and equally precise theoretical calculations.”
The Rancho Del Sol Observatory is located in the foothills of the northern California's Sierra Mountains approximately one hour north of Sacramento. It houses a .5 meter Ritchey-Chretien Telescope. Credit: Ken CrawfordAnd it requires very accurate depictions of studies. According to the team, this pilot survey was conducted with three privately owned observatories equipped with modest sized telescopes located in the USA and Australia. Each observing site features very dark, clear skies with seeing that is routinely at and often below 1.5 arcseconds. These telescopes are manufactured by RC Optical Systems and follow a classic Ritchey-Chretien design. The observatories are commanded with on-site computers that allow remote operation and control from any global location with highband web accesses. Each observatory uses proven, widely available remote desktop control software. Robotic orchestration of all observatory and instrument functions, including multiple target acquisition and data runs, is performed using available scripting software. Additional use of a wide field instrument was employed for those galaxies with an extended angular size. For this purpose, they selected the Astro Physics Starfire 160EDF6, a short focal length (f/7) 16 cm aperture refractor that provides a FOV of 73.7 × 110.6 arcmin. But, it’s more than just taking a photograph. The astrophotographer needs to completely understand what needs to be drawn out of the exposure. It’s more than just taking a “pretty picture”… it’s what matters.
“The galaxy I want to show you has some special features called ‘shells’. I had to image very deep to detect these structures and carefully process them so you can see the delicate structures within.” explains Crawford. “The galaxy name is NGC7600 and these shell structures have not been captured as well in this galaxy before. The movie above shows my image of NGC7600 blending into the simulation at about the point when the shells start to form. The movie below shows the complete simulation.”
“What is ground breaking is that the simulation uses the cold dark matter theory modeling the dark matter halos of the galaxies and as you can see, it is pretty convincing.” concludes Crawford. “So now you all know why we do not observe lots of dwarf galaxies in the Universe.”
But, we can observe some very incredible science done by some very incredible friends. It’s what matters…
Distant quasars shine through the gas-rich "fog" of hot plasma encircling galaxies. At ultraviolet wavelengths, Hubble's Cosmic Origins Spectrograph (COS) is sensitive to absorption from many ionized heavy elements, such as nitrogen, oxygen, and neon. COS's high sensitivity allows many galaxies that happen to lie in front of the much more distant quasars. The ionized heavy elements serve as proxies for estimating how much mass is in a galaxy's halo. (Credit: NASA; ESA; A. Feild, STScI)
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It’s a great question that’s now been validated by the Hubble Space Telescope. Recent observations have shown how galaxies are able to recycle huge amounts of hydrogen gas and heavy elements within themselves. In a process which begins at initial star formation and lasts for billions of years, galaxies renew their own energy sources.
Thanks to the HST’s Cosmic Origins Spectrograph (COS), scientists have now been able to investigate the Milky Way’s halo region along with forty other galaxies. The combined data includes instruments from large ground-based telescopes in Hawaii, Arizona and Chile whose goal was determine galaxy properties. In this colorful instance, the shape and spectra of each individual galaxy would appear to be influenced by gas flow through the halo in a type of “gas-recycling phenomenon”. The results are being published in three papers in the November 18 issue of Science magazine. The leaders of the three studies are Nicolas Lehner of the University of Notre Dame in South Bend, Ind.; Jason Tumlinson of the Space Telescope Science Institute in Baltimore, Md.; and Todd Tripp of the University of Massachusetts at Amherst.
The focus of the research centered on distant stars whose spectra illuminated influxing gas clouds as they pass through the galactic halo. This is the basis of continual star formation, where huge pockets of hydrogen contain enough fuel to ignite a hundred million stars. But not all of this gas is just “there”. A substantial portion is recycled by both novae and supernovae events – as well as star formation itself. It not only creates, but “replenishes”.
The color and shape of a galaxy is largely controlled by gas flowing through an extended halo around it. All modern simulations of galaxy formation find that they cannot explain the observed properties of galaxies without modeling the complex accretion and "feedback" processes by which galaxies acquire gas and then later expel it after chemical processing by stars. Hubble spectroscopic observations show that galaxies like our Milky Way recycle gas while galaxies undergoing a rapid starburst of activity will lose gas into intergalactic space and become "red and dead." (Credit: NASA; ESA; A. Feild, STScI)
However, this process isn’t unique to the Milky Way. Hubble’s COS observations have recorded these recycling halos around energetic star-forming galaxies, too. These heavy metal halos are reaching out to distances of up to 450,000 light years outside the visible portions of their galactic disks. To capture such far-reaching evidence of galactic recycling wasn’t an expected result. According to the Hubble Press Release, COS measured 10 million solar masses of oxygen in a galaxy’s halo, which corresponds to about one billion solar masses of gas – as much as in the entire space between stars in a galaxy’s disk.
So what did the research find and how was it done? In galaxies with rapid star formation, the gases are expelled outward at speed of up to two million miles per hour – fast enough to be ejected to the point of no return – and with it goes mass. This confirms the theories of how a spiral galaxy could eventually evolve into an elliptical. Since the light from this hot plasma isn’t within the visible spectrum, the COS used quasars to reveal the spectral properties of the halo gases. Its extremely sensitive equipment was able to detect the presence of heavy elements, such as nitrogen, oxygen, and neon – indicators of mass of a galaxy’s halo.
So what happens when a galaxy isn’t “green”? According to these new observations, galaxies which have ceased star formation no longer have gas. Apparently, once the recycling process stops, stars will only continue to form for as long as they have fuel. And once it’s gone?
The circled cluster of stars is the dwarf galaxy Andromeda 29, which University of Michigan astronomers have discovered. The bright star within the circle is a foreground star within our own Milky Way galaxy. This image was obtained with the Gemini Multi-Object Spectrograph at the Gemini North telescope in Hawaii. Credit: Gemini Observstory/AURA/Eric Bell
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Yep. It’s that time of year again. Time to enjoy the Andromeda Galaxy at almost every observing opportunity. But now, rather than just look at the nearest spiral to the Milky Way and sneaking a peak at satellites M32 and M110, we can think about something more when we peer M31’s way. There are two newly discovered dwarf galaxies that appear to be companions of Andromeda!
Eric Bell, an associate professor in astronomy, and Colin Slater, an astronomy Ph.D. student, found Andromeda 28 and Andromeda 29 by utilizing the Sloan Digital Sky Survey and a recently developed star counting technique. To back up their observations, the team employed data from the Gemini North Telescope in Hawaii. Located at 1.1 million and 600,000 light-years respectively, Andromeda XXVIII and Andromeda XXIX have the distinction of being the two furthest satellite galaxies ever detected away from the host – M31. Can they be spotted with amateur equipment? Not hardly. This pair comes in about 100,000 fainter than Andromeda itself and can barely be discerned with some of the world’s largest telescopes. They’re so faint, they haven’t even been classified yet.
“With presently available imaging we are unable to determine whether there is ongoing or recent star formation, which prevents us from classifying it as a dwarf spheroidal or a dwarf irregular.” explains Bell.
The dwarf galaxy Andromeda 29, which University of Michigan astronomers have discovered, is clustered toward the middle of this image, obtained with the Gemini North telescope in Hawaii. Credit: Gemini Observstory/AURA/Eric Bell
In their work – published in a recent edition of the edition of the Astrophysical Journal Letters – the team of Bell and Slater explains how they were searching for dwarf galaxies around Andromeda to help them understand how physical matter relates to theoretical dark matter. While we can’t see it, hear it, touch it or smell it, we know it’s there because of its gravitational influence. And when it comes to gravity, many astronomers are convinced that dark matter plays a role in organizing galaxy structure.
“These faint, dwarf, relatively nearby galaxies are a real battleground in trying to understand how dark matter acts at small scales,” Bell said. “The stakes are high.”
Right now, current consensus has all galaxies embedded in surrounding dark matter… and each “bed” of dark matter should have a galaxy. Considering the volume of the Universe, these predictions are pretty much spot on – if we take only large galaxies into account.
“But it seems to break down when we get to smaller galaxies,” Slater said. “The models predict far more dark matter halos than we observe galaxies. We don’t know if it’s because we’re not seeing all of the galaxies or because our predictions are wrong.”
“The exciting answer,” Bell said, “would be that there just aren’t that many dark matter halos.” Bell said. “This is part of the grand effort to test that paradigm.”
Right or wrong… pondering dark matter and dwarf galaxies while observing Andromeda will add a whole new dimension to your observations!
For Further Reading: Andromeda XXVIII: A Dwarf Galaxy more than 350 kpc from Andromeda and Andromeda XXIX: A New Dwarf Spheroidal Galaxy 200 kpc from Andromeda.
A team of scientists has used the NASA/ESA Hubble Space Telescope to observe a quasar accretion disc — a brightly glowing disc of matter that is slowly being sucked into its galaxy’s central black hole. Their study makes use of a novel technique that uses gravitational lensing to give an immense boost to the power of the telescope. The incredible precision of the method has allowed astronomers to directly measure the disc’s size and plot the temperature across different parts of the disc. Image credit: NASA, ESA, J.A. Munoz (University of Valencia)
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Thanks to the magic of the NASA/ESA Hubble Space Telescope, a team of international astronomers have made an incredible observation – a quasar accretion disc surrounding a black hole. By employing a technique known as gravitation lensing, the researchers have been able to get an accurate size measurement and spectral data. While you might not think this exciting at first, know that this type of observation is akin to spotting individual grains of sand on the Moon!
Of course, we know we can’t see a black hole – but we’ve learned a lot about them with time. One of their properties is a bright, visible phenomenon called a quasar. These glowing discs of matter are engaged in orbit around the black hole, much like a coil on an electric stove. As energy is applied, the “coil” heats up and unleashes bright radiation.
“A quasar accretion disc has a typical size of a few light-days, or around 100 billion kilometres across, but they lie billions of light-years away. This means their apparent size when viewed from Earth is so small that we will probably never have a telescope powerful enough to see their structure directly,” explains Jose Munoz, the lead scientist in this study.
Because of the diminutive size of the quasar, most of our understanding of how they work has been based on theory… but great minds have found a way to directly observe their effects. By employing the gravity of stars in an intervening galaxy like a scanning microscope, astronomers have been able to observe the quasar’s light as the stars move. While most of these types of features would be too small to see, the gravitation lensing effect ramps up the strength of the quasar’s light and allows study of the spectra as it cruises across the accretion disc.
This diagram shows how Hubble is able to observe a quasar, a glowing disc of matter around a distant black hole, even though the black hole would ordinarily be too far away to see clearly. Credit: NASA and ESA
By observing a group of gravitationally lensed quasars, the team was able to paint a vivid color portrait of the activity. They were able to pick out small changes between single images and spectral shifts over a period of time. What causes these kaleidoscopic variances? For the most part, it’s the different properties in the gases and dust of the lensing galaxies. Because they travel at different angles to the quasar’s light, scientists were even able to distinguish extinction laws at work.
But there was something special about one of the quasars. Says the Hubble Team, “There were clear signs that stars in the intervening galaxy were passing through the path of the light from the quasar. Just as the gravitational effect due to the whole intervening galaxy can bend and amplify the quasar’s light, so can that of the stars within the intervening galaxy subtly bend and amplify the light from different parts of the accretion disc as they pass through the path of the quasar’s light.”
By documenting these color changes, the team could build a profile of the accretion disc. Unlike our Earthly electric stove coil which glows red as it heats up, the accretion disc of a black hole turns blue as it gets closer to the event horizon. By measuring the blue hue, the team was able to measure the disc diameter and the various tints gave them an indicator of distances from its center. In this case, they found that the disc is between four and eleven light-days across (approximately 100 to 300 billion kilometres). Of course, these are only rough estimates, but considering just how far away we’re looking at such a small object gives these types of observations great potential for future studies… and even improvements on accuracy.
“This result is very relevant because it implies we are now able to obtain observational data on the structure of these systems, rather than relying on theory alone,” says Munoz. “Quasars’ physical properties are not yet well understood. This new ability to obtain observational measurements is therefore opening a new window to help understand the nature of these objects.”
Light echo of dust illuminated by nearby star V838 Monocerotis as it became 600,000 times more luminous than our Sun in January 2002. Credit: NASA/ESA
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Some supermassive black holes are obscured by oddly shaped dust clouds which resemble doughnuts. These clouds have been an unsolved puzzle, but last week a scientist at the University of Leicester proposed a new theory to explain the origins of these clouds, saying that they could be the results of high-speed collisions between planets and asteroids in the central region of galaxies, where the supermassive black holes reside.
While black holes are a death knell for any objects wandering too close, this may mean even planets in a region nearby a black hole are doomed — but not because they would be sucked in. The central regions of galaxies just may be mayhem for planets.
“Too bad for life on these planets, ” said Dr. Sergei Nayakshin, whose paper will be published in the Monthly Notices of the Royal Astronomical Society journal.
In the center of nearly all galaxies are supermassive black holes. Previous studies show that about half of supermassive black holes are obscured by dust clouds.
Nayakshin and his team found inspiration for their new theory from our Solar System, and based their theory on the zodiacal dust which is known to originate from collisions between solid bodies such as asteroids and comets.
The central point of Nayakshin’s theory is that not only are black holes present in the central region of a galaxy, but stars, planets and asteroids as well.
The team’s theory asserts that any collisions between planets and asteroids in the central region of a galaxy would occur at speeds of up to 1000 km/sec. Given the tremendous speeds and energy present in such collisions, eventually rocky objects would be pulverized into microscopic dust grains.
Nayakshin also mentioned that the central region of a galaxy is an extremely harsh environment, given high amounts of deadly radiation and frequent collisions, both of which would make any planets near a supermassive black hole inhospitable well before they were destroyed in any collisions.
While Nayakshin said the frequent collisions would be bad news for any life that may exist on the planets, he added, “On the other hand the dust created in this way blocks much of the harmful radiation from reaching the rest of the host galaxy. This in turn may make it easier for life to prosper elsewhere in the rest of the central region of the galaxy.”
Nayakshin believes that a greater understanding of the origins of the dust near black holes is important to better understand how black holes grow and affect their host galaxy, and concluded with, “We suspect that the supermassive black hole in our own Galaxy, the Milky Way, expelled most of the gas that would otherwise turn into more stars and planets. Understanding the origin of the dust in the inner regions of galaxies would take us one step closer to solving the mystery of the supermassive black holes.”
Composite tricolor images of Stephan's Quintet using H? filters with a recession velocity of 0 (left image) and a recession velocity of 4,200 miles per second (right image).
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While this isn’t a true “cross eye” image, you can darn sure open the larger version, set it to screen size, cross your eyes and get a pretty astonishing result. If you don’t “get it”, then don’t worry. Just look at the pictures separately, because the Subaru Telescope has added a whole new dimension to a seasonal favorite – Stephen’s Quintet. Located in the constellation of Pegasus (RA 22 35 57.5 – Dec +33 57 36), this awesome little galaxy group also known as HIckson Compact Group 92 and Arp 319. In visual observation terms, there’s five – but only four are actually a compact group. The fifth is much closer…
While literally volumes could be written about this famous group, the focus of this article is on the latest observations done by the Subaru Telescope. Each time the “Quints” are observed, it would seem we get more and more information on them! By employing a variety of specialized filters with Subaru’s Prime Focus Camera (Suprime-Cam), the two above images reveal different types of star-formation activity between the closer galaxy – NGC7320 – and the more distant members. It captures Stephen’s Quintet in three dimensions.
So how is it done? Suprime-Cam has the capability of wide field imaging. By utilizing specialized filters, researchers can narrow the photographic process to specific goals. In this instance, they use narrowband filters to reveal star-forming regions within the grouping and their structures. These H-alpha filters are very specific – only allowing a particular wavelength of light to pass through – revealing the hydrogen emissions of starbirth. But here’s the tricky part. The images were taken with two different types of H-alpha filters – each one with a different recession velocity. With a setting of zero, we have an object which is moving away from the observer and close. The other has a greater recession velocity of 4200 miles (6,700 km) per second. This is an indicator of distant objects. For a color palette, red indicates the H-alpha emission lines while blue and green colors assigned to the images from the blue and red filters captured light so that the composite tricolor images aligned with human color perception in red, green, and blue.
When processed, we get the two different views of Stephen’s Quintet as seen above. Says the imaging team; “The image on the left shows the galaxies when the observers used the Ha filter with a recession velocity of 0 while the one on the right shows them when they used the Ha filter with a recession velocity of 4,200 miles per second. The left image shows Ha emissions that indicate an active star-forming region in the spiral arms of NGC7320 in the lower left quadrant but not in the other galaxies. The right image contrasts with the left and shows a region of H-alpha emissions in the upper three galaxies but none from NGC7320. Two (NGC7318A and NGC7318B) of the four galaxies are shedding gas because of a collision while a third (NGC7319) is crashing in, creating shock waves that trigger vigorous star formation.”
But that’s not all. In the figure below we can see the relationship of the galaxies. “Gas stripped from these three galaxies during galactic collisions is ionized by two mechanisms: shock waves and strong ultraviolet light emanating from the newborn stars.” reports the Subaru team. “This ionized gas emits bright light, which the H-alpha filter reveals. Thus the researchers believe that NGC7319 as well as NGC7318A/B are driving the star-forming regions in the Ha emitting region around NGC7318A/B.”
A diagram of the member galaxies of Stephan's Quintet. NGC7320 is a closer galaxy and has a recession velocity of 0. The remaining four are a group of more distant galaxies 300 million light years away. The researchers believe that the merging of NGC7318A/B and NGC7319's crashing into them are responsible for the active star formation regions in the Ha emitting region around NGC7318A/B.
But star-forming activity isn’t all you can derive from these images – they are also an indicator of distance. By exposing opposing recession velocities in the same image, observers are able to deduce where objects are located at different distances, yet close to each other. “The contrasting images show that NGC7320 is closer than the other galaxies, which show active star formation at a significantly higher recession velocity (4,200 miles per second) than NGC7320 (0).” explains the team. “NGC7320 is about 50 million light years away while the other four galaxies are about 300 million light years away. This explains the intriguing arrangement of the galaxies in Stephan’s Quintet.”
Now is a great time to observe this cool cluster of galaxies for yourself… Before the Moon interferes again!
Galactic Wrecks Far from Earth: These images from NASA's Hubble Space Telescope's ACS in 2004 and 2005 show four examples of interacting galaxies far away from Earth. The galaxies, beginning at far left, are shown at various stages of the merger process. The top row displays merging galaxies found in different regions of a large survey known as the AEGIS. More detailed views are in the bottom row of images. (Credit: NASA; ESA; J. Lotz, STScI; M. Davis, University of California, Berkeley; and A. Koekemoer, STScI)
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Big galaxies… Little galaxies… But how often do they meet? Thanks to information from some of the latest Hubble surveys, astronomers have been able to more closely estimate galaxy collision rates than ever before. Apparently those that have happened within the last eight to nine billion years have occurred somewhere in-between previous estimates.
When it comes to galaxy evolution, the collision rate is an indicator of how individual galaxies accumulated mass over time. While it’s pretty much a standard measurement, there’s a large margin with no information of how often it might have occurred in the very distant past. By taking a look at in deep-field surveys made by NASA’s Hubble Space Telescope, astronomers were able to get a general look – one that showed a merger rate of anywhere from 5 percent to 25 percent of those studied.
The science team, led by Jennifer Lotz of the Space Telescope Science Institute in Baltimore, Maryland, took a close look at galaxy interactions spaced over vast distances. This allowed the group to essentially study mergers which occurred at different times. What they found was larger galaxies had a merger rate of once every nine billion years, while smaller ones crashed up more often. When taking a look a dwarf galaxies compared to massive ones, the team found it happened three times more often than the rate for large galaxies.
“Having an accurate value for the merger rate is critical because galactic collisions may be a key process that drives galaxy assembly, rapid star formation at early times, and the accretion of gas onto central supermassive black holes at the centers of galaxies,” Lotz explains.
While there were past studies of galaxy mergers done with Hubble information, astronomers used a different method and came up with different results. “These different techniques probe mergers at different ‘snapshots’ in time along the merger process,” Lotz says. “It is a little bit like trying to count car crashes by taking snapshots. If you look for cars on a collision course, you will only see a few of them. If you count up the number of wrecked cars you see afterwards, you will see many more. Studies that looked for close pairs of galaxies that appeared ready to collide gave much lower numbers of mergers than those that searched for galaxies with disturbed shapes, evidence that they’re in smashups.”
To help determine how often the merger rate occurred with time, Lotz and her team had to know how long an encountered galaxy would appear disrupted. In order to get a good working model, the team used computer simulations and then mapped them compared to Hubble images of galaxy interactions. While this effort took a great deal of time, the team did their best to create every possible scenario – from a pair of galaxies with equal mass to disparate ones. They also took into account orbits, collisional events and even orientation. Of these studies, 57 different situations and 10 viewing angles were accounted for. “Viewing the simulations was akin to watching a slow-motion car crash,” Lotz says. These computer created scenarios followed the galaxies for 2 billion to 3 billion years, starting at the merger beginning and ending a billion years later when completed. “Our simulations offer a realistic picture of mergers between galaxies,” explains Lotz.
While it was easy enough to see what happens with a giant galaxy, it was a bit more difficult to observe what happens with diminutive ones. Observing a dwarf merger is far more difficult simply because they are so much more dim – but plentiful. “Dwarf galaxies are the most common galaxy in the universe,” Lotz says. “They may have contributed to the buildup of large galaxies. In fact, our own Milky Way galaxy had several such mergers with small galaxies in its recent past, which helped to build up the outer regions of its halo. This study provides the first quantitative understanding of how the number of galaxies disturbed by these minor mergers changed with time.”
However, studies of this type just don’t happen with a handful of photos. Lotz and the team had to compare the simulations with literally thousands of galaxy images taken from some of Hubble’s largest surveys, including the All-Wavelength Extended Groth Strip International Survey (AEGIS), the Cosmological Evolution Survey (COSMOS), and the Great Observatories Origins Deep Survey (GOODS), as well as mergers identified by the DEEP2 survey with the W.M. Keck Observatory in Hawaii. At the beginning they found a wide variety of merger rates, but ended up with about a thousand merger candidates. “When we applied what we learned from the simulations to the Hubble surveys in our study, we derived much more consistent results,” Lotz says.
What’s next for Lotz and her team? It’s time to take a look at galaxy interactions that happened about 11 billion years ago. Their goal is to check out when star formation across the Universe reached its greatest as compared to the merger rate. Perhaps there might be a correlation between encounters and rapid star birth!
Two examples of galaxy pairs in the COSMOS survey (courtesy of the Chandra X-ray Center). The Hubble Space Telescope images show galaxies undergoing a close encounter (shown in gold). X-rays, as detected by Chandra, indicate which of the two galaxies hosts an AGN. In addition, diffuse X-ray emission from hot gas is present thus highlighting that such galaxy associations tend to reside in galaxy groups, an environment of rapid galaxy and black hole growth.
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Yep. It’s true. Almost all galaxies are guilty of having a supermassive black hole in their centers. Some even tip the scales at millions – or even billions – of times more mass than the Sun. However, how they came to be so weighty is a true enigma. Thanks to research done by Dr. John Silverman (IPMU) and the international COSMOS team, the Chandra X-Ray Observatory and the European Southern Observatory’s Very Large Telescope have revealed that galaxy interactions may be responsible for the growth of supermassive black holes – and they’ve left behind some very important clues…
If you’re big – you’re big. As a general rule, supermassive black holes like to hang out in massive galaxies. Their mass is usually directly related to the central bulge. Now the consensus is that massive galaxies gained their girth (at least in part) by mergers and interactions with smaller galaxies. This act of cannibalism in galactic evolution has been postulated to explain how matter gathers toward the middle, eventually resulting in a supermassive black hole.
How do we determine this? One way is to take a closer look at galaxies currently in merger as compared to ones in isolation. While the concept is easy, carrying out the test hasn’t been. A supermassive black hole leaves visual observations “blinded by the light” while a quasar can effectively “outshine” an entire host galaxy, leaving an interactor almost impossible to detect. But, like a bulging waistline, such interactions should distort the overall contours of the galaxy.
Now the COSMOS team might have an answer to the riddle.. by assuming a galaxy is interacting if it has a nearby neighbor. It’s a test that can happen without needing to know if distortion is present in optical images. What makes it possible are accurate distance measurements of about 20,000 galaxies in the COSMOS field as provided by the zCOSMOS redshift survey with the European Southern Observatory’s Very Large Telescope. Isolated galaxies are used to give a comparison sample to lay the foundation as to whether an active galactic nucleus is common to interacting galaxies. With help from NASA’s Chandra Observatory, X-ray observations pinpoint galaxies which host an AGN. The X-ray emission signature dominates in growing SMBHs and X-rays are capable of cutting through the gas and dust of star-forming regions.
In their report to The Astrophysical Journal the team states that galaxies in close pairs are twice as likely to harbor AGNs as compared to galaxies in isolation. This answer may prove that beginning galaxy interactions can lead to “enhanced black hole growth”. Because it’s not a drastically common occcurrance, it means that only about 20% of SMBHs that break the scale happen via a merger event and that “final coalescence” might also play a role.
One thing we do know is that galaxies and their black holes, like people and their waistlines, all get a little heavier with time.
