New Hubble image of Messier 9 cluster resolves individual stars (NASA/ESA)
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First discovered by Charles Messier in 1764, the globular cluster Messier 9 is a vast swarm of ancient stars located 25,000 light-years away, close to the center of the galaxy. Too distant to be seen with the naked eye, the cluster’s innermost stars have never been individually resolved… until now.
This image from the Hubble Space Telescope is the most detailed view yet into Messier 9, capturing details of over 250,000 stars within it. Stars’ shape, size and color can be determined — giving astronomers more clues as to what the cluster’s stars are made of. (Download a large 10 mb JPEG file here.)
Hot blue stars as well as cooler red stars can be seen in Messier 9, along with more Sun-like yellow stars.
Unlike our Sun, however, Messier 9’s stars are nearly ten billion years old — twice the Sun’s age — and are made up of much less heavy elements.
Since heavy elements (such as carbon, oxygen and iron) are formed inside the cores of stars and dispersed into the galaxy when the stars eventually go supernova, stars that formed early on were birthed from clouds of material that weren’t yet rich in such elements.
Zoom into the Messier 9 cluster with a video from NASA and the European Space Agency below:
The Hubble Space Telescope is a project of international cooperation between ESA and NASA. See more at www.spacetelescope.org.
Image credit: NASA & ESA. Video: NASA, ESA, Digitized Sky Survey 2, N. Risinger (skysurvey.org)
Mosaic of infrared survey images from ESO's VISTA reveal over 200,000 distant galaxies. (ESO/UltraVISTA team. Acknowledgement: TERAPIX/CNRS/INSU/CASU.)
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See all those tiny points of light in this image? Most of them aren’t stars; they’re entire galaxies, seen by the European Southern Observatory’s VISTA survey telescope located at the Paranal Observatory in Chile.
This is a combination of over 6000 images taken with a total exposure time of 55 hours, and is the widest deep view of the sky ever taken in infrared light.
The galaxies in this VISTA image are only visible in infrared light because they are very far away. The ever-increasing expansion rate of the Universe shifts the light coming from the most distant objects (like early galaxies) out of visible wavelengths and into the infrared spectrum.
ESO’s VISTA (Visual and Infrared Survey Telescope for Astronomy) telescope is the world’s largest and most powerful infrared observatory, and has the ability to peer deep into the Universe to reveal these incredibly distant, incredibly ancient structures.
By studying such faraway objects astronomers can better understand how the structures of galaxies and galactic clusters evolved throughout time.
The region seen in this deep view is an otherwise “unremarkable” and apparently empty section of sky located in the constellation Sextans.
A unique galaxy, which holds clues to the evolution of galaxies billions of years ago, has now been discovered by an Indian-led international team of astronomers. The discovery, which will enable scientists to unearth new aspects about the formation of galaxies in the early universe, has been made using the Giant Meterwave Radio Telescope (GMRT) of the National Centre for Radio Astrophysics, Tata Institute of Fundamental Research (NCRA-TIFR). CREDIT: Hota et al., SDSS, NCRA-TIFR, NRAO/AUI/NSF.
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Its name is SPECA – a Spiral-host Episodic radio galaxy tracing Cluster Accretion. That’s certainly a mouthful of words for this unusual galaxy, but there’s a lot more going on here than just its name. “This is probably the most exotic galaxy with a black hole, ever seen. It is like a ‘missing-link’ between present day and past galaxies. It has the potential to teach us new lessons about how galaxies and clusters of galaxies formed in the early Universe,” said Ananda Hota, of the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), in Taiwan and who discovered this exotic galaxy.
Located about 1.7 billion light-years from Earth, Speca is a radio source that contains a central supermassive black hole. As we have learned, galaxies of this type produce relativistic “jets” which are responsible for being bright at the radio frequencies, but that’s not all they create. While radio galaxies are generally elliptical, Speca is a spiral – reason behind is really unclear. As the relativistic jets surge with time, they create lobes of sub-atomic material at the outer edges which fan out as the material slows down… and Speca is one of only two galaxies so far discovered to show this type of recurrent jet activity. Normally it occurs once – and rarely twice – but here it has happened three times! We are looking at a unique opportunity to unravel the mysteries of the beginning phase of a black hole jet.
“Both elliptical and spiral galaxies have black holes, but Speca and another galaxy have been seen to produce large jets. It is also one of only two galaxies to show that such activity occurred in three separate episodes.” explains Sandeep Sirothia of NCRA-TIFR. “The reason behind this on-off activity of the black hole to produce jets is unknown. Such activities have not been reported earlier in spiral galaxies, which makes this new galaxy unique. It will help us learn new theories or change existing ones. We are now following the object and trying to analyse the activities.”
Dr. Hota and an international team of scientists reached their first conclusions while studying combined data from the visible-light Sloan Digital Sky Survey (SDSS) and the FIRST survey done with the Very Large Array (VLA) radio telescope. Here they discovered an unusually high rate of star formation where there should be none and they then confirmed their findings with ultraviolet data from NASA’s GALEX space telescope. Then the team dug even deeper with radio information obtained from the NRAO VLA Sky Survey (NVSS). At several hundred million years old, these outer lobes should be beyond their reproductive years… Yet, that wasn’t all. GMRT images displayed yet another, tiny lobe located just outside the stars at the edge of Speca in plasma that is just a few million years old.
“We think these old, relic lobes have been ‘re-lighted’ by shock waves from rapidly-moving material falling into the cluster of galaxies as the cluster continues to accrete matter,” said Ananda. “All these phenomena combined in one galaxy make Speca and its neighbours a valuable laboratory for studying how galaxies and clusters evolved billions of years ago.”
As you watch the above galaxy merger simulation created by Tiziana Di Matteo, Volker Springel, and Lars Hernquist, you are taking part in a visualization of two galaxies combining which both have central supermassive black holes and the gas distribution only. As they merge, you time travel over two billion years where the brightest hues indicate density while color denotes temperature. Such explosive process for the loss of gas is needed to understand how two colliding star-forming spiral galaxies can create an elliptical galaxy… a galaxy left with no fuel for future star formation. Outflow from the supernovae and central monster blackholes are the prime drivers of this galaxy evolution.
“Similarly, superfast jets from black holes are supposed to remove a large fraction of gas from a galaxy and stop further star formation. If the galaxy is gas-rich in the central region, and as the jet direction changes with time, it can have an adverse effect on the star formation history of a galaxy. Speca may have once been part of such a scenario. Where multiple jets have kicked out spiral arms from the galaxy. To understand such a process Dr Hota’s team has recently investigated NGC 3801 which has very young jet in very early-phase of hitting the host galaxy. Dust/PAH, HI and CO emission shows an extremely warped gas disk. HST data clearly showa outflow of heated-gas. This gas loss, as visualised in the video, has possibly caused the decline of star formation. However, the biggest blow from the monster’s jets are about to give the knock-down punch the galaxy.
“It seems, we observe this galaxy at a rare stage of its evolutionary sequence where post-merger star formation has already declined and new powerful jet feedback is about to affect the gaseous star forming outer disk within the next 10 million years to further transform it into a red-and-dead early-type galaxy.” Dr. Hota says.
The causes behind why present day radio galaxies do not contain a young star forming disks are not clear. Speca and NGC 3801 are ideal laboratories to understand black hole galaxy co-evolution processes.
LEDA 074886: a dwarf galaxy with a curious rectangular shape
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It’s being called the “emerald-cut galaxy” — recently discovered by an international team of astronomers with the Swinburne University of Technology in Australia, LEDA 074886 is a dwarf galaxy located 70 million light-years (21 Mpc) away, within a group of about 250 other galaxies.
“It’s an exciting find,” Dr. Alister Graham, lead author and associate professor at Swinburne University Center for Astrophysics and Supercomputing told Universe Today in an email. “I’ve seen thousands of galaxies, and they don’t look like this one.”
The gem-cut galaxy was detected in a wide-field image taken with the Japanese Subaru Telescope by astrophysicist Dr. Lee Spitler.
It’s thought that the unusual shape is the result of a collision between two galaxies, possibly two former satellite galaxies of the larger NGC 1407, the brightest of all the approximately 250 galaxies within its local group.
“At first we thought that there was probably some gravitational-tidal interaction which has caused LEDA 074886 to have its unusual shape, but now we’re not so sure, as its features better match that of two colliding disk galaxies,” Dr. Graham said.
In addition to being oddly angular, LEDA 074886 also features a stellar disk inside it, aligned edge-on to our line of sight. This disk of stars is rotating at speeds of up to 33 km/second, although it can’t be discerned if it has a spiral structure or not because of our position relative to it.
False-color image of LEDA 074886 taken with Subaru Telescope's Suprime-Cam. Contrast enhanced to show central disk structure. (Graham et al.)
“It’s one of those things that just makes you smile because it shouldn’t exist, or rather you don’t expect it to exist.”
– Dr. Alister Graham, Associate Professor, Swinburne University of Technology
Although rectangular galaxies are rare, we may eventually become part of one ourselves.
“Curiously,” Dr. Graham said, “if the orientation was just right, when our own disc-shaped galaxy collides with the disc-shaped Andromeda galaxy about three billion years from now we may find ourselves the inhabitants of a square-looking galaxy.”
(Let’s hope that it’s still “hip to be square” in another 3 billion years!)
The team’s paper will be published in The Astrophysical Journal. Read more on the Swinburne University press release here or on the Subaru Telescope site.
Images of the six galaxies with detected inflows taken with the Advanced Camera for Surveys on the Hubble Space Telescope. Most of these galaxies have a disk-like, spiral structure, similar to that of the Milky Way. Star formation activity occurring in small knots is evident in several of the galaxies' spiral arms. Because the spirals appear tilted in the images, Rubin et al. concluded that we are viewing them from the side, rather than face-on. This orientation meshes well with a scenario of 'galactic recycling' in which gas is blown out of a galaxy perpendicular to its disk, and then falls back in at different locations along the edge of the disk. Credit: K. Rubin, MPIA
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Got a teenager? Then you know the story. Go to look for your favorite bag of chips and they’re gone. You eat one portion of meat and they need three. If you like those cookies, then you better have a darn good place to stash them. And, while you’re at it, their car needs gas. Apparently there’s a reason for the word “universal”, because teenage galaxies aren’t much different. Thanks to some new studies done by ESO’s Very Large Telescope, astronomers have been able to take a much closer look at adolescent galaxies and their “feeding habits” during their evolution. Some 3 to 5 billion years after the Big Bang they were happiest when just provided with gas, but later on they developed a voracious appetite… for smaller galaxies!
Scientists have long been aware that early galaxy structures were much smaller than the grand spirals and hefty ellipticals which fill the present Universe. However, figuring out exactly how galaxies put on weight – and where the bulk supply comes from – has remained an enigma. Now an international group of astronomers have taken on more than a hundred hours of observations taken with the VLT to help determine how gas-rich galaxies developed.
“Two different ways of growing galaxies are competing: violent merging events when larger galaxies eat smaller ones, or a smoother and continuous flow of gas onto galaxies.” explains team leader, Thierry Contini (IRAP, Toulouse, France). “Both can lead to lots of new stars being created.”
The undertaking is is MASSIV – the Mass Assembly Survey with the VIsible imaging Multi-Object Spectrograph, a powerful camera and spectrograph on the VLT. It’s incredible equipment used to measure distance and properties of the surveyed galaxies Not only did the survey observe in the near infrared, but also employed a integral field spectrograph and adaptive optics to refine the images. This enables astronomers to map inner galaxy movements and content, as well as leaving room for some very surprising results.
“For me, the biggest surprise was the discovery of many galaxies with no rotation of their gas. Such galaxies are not observed in the nearby Universe. None of the current theories predict these objects,” says Benoît Epinat, another member of the team.
“We also didn’t expect that so many of the young galaxies in the survey would have heavier elements concentrated in their outer parts — this is the exact opposite of what we see in galaxies today,” adds Thierry Contini.
These results point towards a major change during the galactic “teenage years”. At some time during the young Universe state, smooth gas flow was a considerable building block – but mergers would later play a more important role.
“To understand how galaxies grew and evolved we need to look at them in the greatest possible detail. The SINFONI instrument on ESO’s VLT is one of the most powerful tools in the world to dissect young and distant galaxies. It plays the same role that a microscope does for a biologist,” adds Thierry Contini.
The team plans on continuing to study these galaxies with future instruments on the VLT as well as using ALMA to study the cold gas in these galaxies. However, their work with gas isn’t the only “station” on the block. In a separate study led by Kate Rubin (Max Planck Institute for Astronomy), the Keck I telescope on Mauna Kea, Hawaii, has been used to examine gas associated with a hundred galaxies at distances between 5 and 8 billion light-years – the older teens. They have found initial evidence of gas flowing back into distant galaxies that are actively forming new stars.
Images of the six galaxies with detected inflows taken with the Advanced Camera for Surveys on the Hubble Space Telescope. Most of these galaxies have a disk-like, spiral structure, similar to that of the Milky Way. Star formation activity occurring in small knots is evident in several of the galaxies' spiral arms. Because the spirals appear tilted in the images, Rubin et al. concluded that we are viewing them from the side, rather than face-on. This orientation meshes well with a scenario of 'galactic recycling' in which gas is blown out of a galaxy perpendicular to its disk, and then falls back in at different locations along the edge of the disk. Credit: K. Rubin, MPIA
Apparently, like a teenager with the munchies, matter finds its way into those galactic tummies. One feeding theory is an inflow from huge low-density gas reservoirs filling the intergalactic voids… another is huge cosmic matter cycle. While there is very little evidence to support either hypothesis, gases have been observed to flow away from some galaxies and may be moshed around by several different sources – such as supernovae events or peer pressure from gigantic stars.
“As this gas drifts away, it is pulled back by the galaxy’s gravity, and could re-enter the same galaxy in time scales of one to several billion years. This process might solve the mystery: the gas we find inside galaxies may only be about half of the raw material that ends up as fuel for star formation.” says Dr. Rubin. “Large amounts of gas are caught in transit, but will re-enter the galaxy in due time. Add up the galaxy’s gas and the gas currently undergoing cosmic recycling, and there is a sufficient amount of raw matter to account for the observed rates of star formation.”
It might very well be a case of cosmic recycling… but I’d feel safer hiding my cookies.
Today's Journal Club is about a new addition to the Standard Model of fundamental particles.
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According to Wikipedia, a journal club is a group of individuals who meet regularly to critically evaluate recent articles in the scientific literature. And of course, the first rule of Journal Club is… don’t talk about Journal Club.
So, without further ado – today’s journal article is about dark matter being in the wrong place at the wrong time.
This time, rather than someone suggesting what the next journal club article would be (like that happens), I thought I would pick a topical scientific paper mentioned in one of Universe Today’s fabulously thought-provoking stories and enlarge on that a bit.
So, some might remember the Bullet Cluster – a seemingly clinching proof of dark matter, where two galactic clusters had collided in the past and what we see post-collision is that most of the mass of each cluster has passed straight through and out the other side. The only material remaining at the collision site is a huge jumbled clump of intergalactic gas.
This means that each galactic cluster, that has since moved on, has been stripped of much of its intergalactic gas. But lo and behold the seemingly empty intergalactic space within each of these stripped galactic clusters continues to distort the background field of view (a phenomenon known as weak gravitational lensing).
This seemed strong proof that the intergalactic spaces of each cluster must be filled with gravitationally-inducing, but otherwise invisible, stuff. In other words, dark matter. It makes sense that this dark matter would have moved straight on through the collision site because it is weakly interacting – whereas the gas caught up in the collision was not.
So, a cool finding and almost identical findings were discovered within the cluster collisions MACS J0025.4-1222, Abell 2744 and a couple of others. But now along comes Abell 520 with a completely counter example. Two or more galaxy clusters have collided, most of the visible contents have passed straight through, but back at the collision point is an apparent big clump of invisible stuff creating weak gravitational lensing – i.e. dark matter. It is the region labelled 3 on the figure at page 5 of the article.
This finding requires us to consider that we had naively concluded that the Bullet Cluster’s post-collision appearance was easily interpretable and that its outcome would surely be repeated in any equivalent collision of galaxy clusters.
But in the wake of Abell 520 we now may need to consider that the outcome of a collision between rapidly moving and utterly gargantuan collections of mass is much more complex and unpredictable than we had initially assumed. This doesn’t mean that the dark matter hypothesis has been debunked, it just means that the Bullet Cluster might not have been the clinching proof that we thought it was.
If we subsequently find fifty new Bullet cluster analogues and no more Abell 520 analogues, we might then assume that Abell 520 is just a weird outlier, which can be dismissed as an unrepresentative anomaly. But with only five or six such collision types known, one of which is Abell 520 – we can’t really call it an outlier at the moment.
So… comments? The authors offers six possible scenarios to explain this finding – got a seventh? Did we jump to conclusions with the Bullet Cluster? Could suggestions for an article for the next edition of Journal Club represent a form of negative energy?
An infared image of the cluster. Three narrow slices of the infrared spectrum are represented in this color composite. The colors have been balanced to accentuate the red galaxies at a distance of 10.5 billion light years. Credit: FourStar Galaxy Evolution Survey ("Z-FOURGE")
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Located some 10.5 billion light years away in the general direction of the constellation of Leo, the most distant cluster of red galaxies so far discovered has been hiding in plain sight… until now. Thanks to the advanced observing techniques of FourStar, a new and powerful near-infrared camera on the 6.5m Magellan Baade Telescope, we’re now able to peer beyond faint and into the realm of the faintest. It’s 30 galaxies packed like sardines in a tin and their formation is the earliest known “galaxy city” in the Universe!
“These are the first steps of accurately measuring the rate at which these large urban cities formed in a dark-matter-dominated universe,” says Texas A&M astronomer, Dr. Casey Papovich. “The rate at which they come together tests our understanding of how structures in the universe formed. The broader the timeline, the better our chances of being accurate. Instrumentation is key, and as it evolves, we’ll keep pushing the boundaries.”
Up until now, this galaxy conglomeration had remained undisclosed – despite thousand upon thousands of hours of survey images taken in their area. It is truly amazing that they were overlooked by the huge ground-based telescopes and space-based research instruments, including the Hubble Space Telescope. There was just no accurate distance estimations until the FourStar project came along. Headed by Eric Persson of the Carnegie Observatories, the stellar team includes Carnegie’s David Murphy, Andy Monson, Dan Kelson, Pat McCarthy, and Ryan Quadri – a group whose findings will be published in the Astrophysical Journal Letters.
Just what is FourStar? It’s a specialized camera set with a group of five very specific filters which are sensitively tuned to a very narrow portion of the near-infrared spectrum. “These new filters are a novel approach; it’s a bit like being able to do a CAT scan of the sky to rapidly make a 3-D picture of the early universe,” says Swinburne’s Karl Glazebrook, who is leading the Australian component of the international collaboration formed in 2009.What sets it apart is its ability to accurately measure distances between Earth and target galaxies one at a time. This allows the program to build an incredible three-dimensional look at the source point.
“Most other surveys were just looking at the tip of the iceberg,” Dr. Kim-Vy Tran explains. “The modern technology contained in this camera enabled us to detect the faintest light possible, allowing us to see much more of the iceberg than previously revealed. It’s like we’re using a comb to sift through the very distant universe. The combination of filters and depth provided by this camera give us the equivalent of more teeth, resulting in better measurements and more accurate results.”
The survey was built one deep over an 11×11 arcminute field each in COSMOS, CDFS and UDS. When it comes to galaxy properties, they are looking at 1-2% accurate redshifts and the current 3-D map is looking back to when the Universe was only 3 billion years old.
“This means the galaxy cluster is still young and should continue to grow into an extremely dense structure possibly containing thousands of galaxies,” explained lead author Lee Spitler of Australia’s Swinburne University of Technology.
The FourStar Galaxy Evolution Survey (“Z-FOURGE”) is just the beginning. Through studies of clusters like this one, astronomers can and will get a better understanding of how galaxy clusters evolve in relationship to their environments and – possibly – how they assemble into larger structures. The survey, led by Dr. Ivo Labbé, a former Carnegie postdoctoral fellow, now at Leiden Observatory in the Netherlands, will also strengthen our abilities to determine distances. In just a half a year, the team “has obtained accurate distances for faint galaxies over a region roughly one-fifth the apparent size of the Moon” locating about another thousand galaxies at even further extents.
“The excellent image quality and sensitivity of Magellan and FourStar really make the difference,” Labbé said. “We look forward to many more exciting and unexpected discoveries!”
Today's Journal Club is about a new addition to the Standard Model of fundamental particles.
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According to Wikipedia, a journal club is a group of individuals who meet regularly to critically evaluate recent articles in the scientific literature. And of course, the first rule of Journal Club is… don’t talk about Journal Club.
So, without further ado – today’s journal article is about dark matter and how to determine where it is and how dense it is – although still without actually seeing it.
We can see how the gravitational influence of invisible dark matter is affecting the general morphology of a galaxy and the motion of the stars within that galaxy. These factors can then hint at where the dark matter is and how dense it is.
Traditional thinking positions dark matter in a halo shape around a galaxy – meaning more of it is outward than inward – which helps explain why visible objects in the outer rim of a galaxy seem to orbit the galactic center at about the same periodicity as inner visible objects. This is contrary to our local Keplerian understanding of orbital mechanics where close-in Mercury orbits the Sun (containing over 99% of the solar system’s mass) in 88 days while distant Neptune takes a leisurely 165 years.
We assume galaxies’ relatively even periodicities are a result of each galaxy’s total mass (visible and dark) being distributed throughout its structure and not concentrated in its center.
The authors use the term ‘early-type’ galaxy to describe their target population for this research. ‘Early-type’ seems unnecessary jargon – being a reference to the Hubble sequence, for which Hubble explained at some length that he was just putting galaxies in a sequence for ease of classification and he did not mean to imply any temporal sequence from the arrangement.
As it happens, our modern understanding is that these ‘early’ types, the elliptical and lenticular galaxies, are actually some of the oldest galaxy forms around. Young galaxies tend to be bright spirals. Over time, these spirals either fade, so you no longer see their spiral arms (lenticulars), or they collide with other galaxies and their ageing stars get jumbled up into random orbits to form big, blobby shapes (ellipticals).
So everywhere you see ‘early-type’ in this article – you should substitute elliptical and lenticular. Jargon prevents the general reader from being able to follow the meaning of a specialist writer – you don’t have to do this to be a scientist.
Anyhow, the researchers conducted a statistical analysis of the estimated stellar mass values and velocity dispersions of star populations within different elliptical and lenticular galaxies. Their objective was to try and get a fix on the distribution of the invisible dark matter that we think all galaxies contain.
Their analysis found that dark matter was more concentrated towards the centers of elliptical and lenticular galaxies – and the authors conclude that nearby elliptical and lenticular galaxies might hence be ideal candidates for the identification of gamma ray output from dark matter annihilation.
The last suggestion seems a bit of an intellectual leap. There have been a few reported observations of radiation output of uncertain origin from the centers of galaxies. Dark matter annihilation has been one suggested cause – but you’d think there’s a lot of stuff going on in the center of a galaxy that could offer an alternate explanation.
I could not find in the paper any suggestions as to why ‘halo contraction’ (presumably jargon for ‘dark matter concentration’) occurs in these galaxy types more often than others – which seemed the more obvious point to offer speculation on.
So… comments? Why, when knowing diddly-squat about the particle nature of dark matter, should we assume it possesses the ability to self-annihilate? Is ‘early-type’ unnecessary jargon or entrenched terminology? Is the question ‘does anyone want to suggest an article for the next edition of Journal Club’ just rhetorical?
The sprawling northern constellation of Draco is home to a monumental galactic merger which left a singular spectacle – NGC 5907. Surrounded by an ethereal garment of wispy star trails and currents of stellar material, this spiral galaxy is the survivor of a “clash of the dragons” which may have occurred some 8 to 9 billion years ago. Recent theory suggests galaxies of this type may be the product of a larger galaxy encountering a smaller satellite – but this might not be the case. Not only is NGC 5907 a bit different in some respects, it’s a lot different in others… and peculiar motion is just the beginning.
“If the disc of many spirals is indeed rebuilt after a major merger, it is expected that tidal tails can be a fossil record and that there should be many loops and streams in their halos. Recently Martínez-Delgado et al. (2010) have conducted a pilot survey of isolated spiral galaxies in the Local Volume up to a low surface brightness sensitivity of ~28.5 mag/arcsec2 in V band. They find that many of these galaxies have loops or streams of various shapes and interpret these structures as evidence of minor merger or satellite infall.” says J. Wang of the Chinese Academy of Sciences. “However, if these loops are caused by minor mergers, the residual of the satellite core should be detected according to numerical simulations. Why is it hardly ever detected?”
The “why” is indeed the reason NGC 5907 is being intensively studied by a team of six scientists of the Observatoire de Paris, CNRS, Chinese Academy of Sciences, National Astronomical Observatories of China NAOC and Marseille Observatory. Even though NGC 5907 is a member of a galactic group, there are no galaxies near enough to it to be causing an interaction which could account for its streamers of stars. It is truly a warped galaxy with gaseous and stellar disks which extend beyond the nominal cut-off radius. But that’s not all… It also has a peculiar halo which includes a significant fraction of metal enriched stars. NGC 5907 just doesn’t fit the patterns.
“For some of our models, we assume a star formation history with a varying global efficiency in transforming gas to stars, in order to preserve enough gas from being consumed before fusion.” explains the research team. “Although this fine-tuned star formation history may have some physical motivations, its main role is also to ensure the formation of stars after the emergence of the gaseous disc just after fusion.”
On left, the NGC 5907 galaxy. It is compared to the simulations, on right. Both cases show an edge-on galactic disk surrounded by giant loops of old stars, which are witnessing of a former, gigantic collision. (Jay Gabany, cosmotography.com / Observatoire de Paris / CNRS / Pythéas / NAOC)
Now enter the 32- and 196-core computers at the Paris Observatory center and the 680-core Graphic Processor Unit supercomputer of Beijing NAOC with the capability to run 50000 billion operations per second. By employing several state of the art, hydrodynamical, and numerical simulations with particle numbers ranging from 200 000 to 6 millions, the team’s goal was to show the structure of NGC 5907 may have been the result of the clash of two dragon-sized galaxies… or was it?
“The exceptional features of NGC 5907 can be reproduced, together with the central galaxy properties, especially if we compare the observed loops to the high-order loops expected in a major merger model.” says Wang. “Given the extremely large number of parameters, as well as the very numerous constraints provided by the observations, we cannot claim that we have already identified the exact and unique model of NGC 5907 and its halo properties. We nevertheless succeeded in reproducing the loop geometry, and a disc-dominated, almost bulge-less galaxy.”
In the meantime, major galaxy merger events will continue to be a top priority in formation research. “Future work will include modelling other nearby spiral galaxies with large and faint, extended features in their halos.” concludes the team. “These distant galaxies are likely similar to the progenitors, six billion years ago, of present-day spirals, and linking them together could provide another crucial test for the spiral rebuilding disc scenario.”
The Galactic globular cluster M80 in the constellation Scorpius contains several hundred thousand stars. Credit: HST/NASA/ESA
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It seems logical to assume that long ago, the amount of globular clusters increased in our galaxy during star-making frenzies called ‘starbursts.’ But a new computer simulation shows just the opposite: 13 billion years ago, starbursts may have actually destroyed many of the globular clusters that they helped to create.
“It is ironic to see that starbursts may produce many young stellar clusters, but at the same time also destroy the majority of them,” said Dr. Diederik Kruijssen of the Max Planck Institute for Astrophysics. “This occurs not only in galaxy collisions, but should be expected in any starburst environment”
Astronomers have wondered why throughout the Universe, typical globular star clusters contain about the same number of stars. In contrast much younger stellar clusters can contain almost any number of stars, from fewer than 100 to many thousands.
The new computer simulation by Kruijssen and his team proposes that this difference could be explained by the conditions under which globular clusters formed early on in the evolution of their host galaxies.
In the early Universe, starbursts were common. Large galaxies were in clusters, and collisions occurred often. The computer simulation showed that during starbursts, gas, dust and stars were still being sloshed around from the galaxy collision, with the pull of gravity on the globular clusters constantly changing. This was enough to rip apart most of the globular clusters and only the biggest ones were strong enough to survive. The simulations showed most of the star clusters were destroyed shortly after their formation, when the galactic environment was still very hostile to the young clusters. But after the environment calmed down, the surviving globular clusters have survived – now living quietly – and we can still enjoy their beauty.
In their paper, the astronomers say that this explains why the number of stars contained within globular clusters is roughly the same across the entire Universe. “It therefore makes perfect sense that all globular clusters have approximately the same large number of stars,” said Kruijssen. “Their smaller brothers and sisters that didn’t contain as many stars were doomed to be destroyed.”
Kruijssen and his team said that while the very brightest and largest clusters were capable of surviving the galaxy collision due to their own gravitational attraction, numerous smaller clusters were effectively destroyed by the rapidly changing gravitational forces.
The fact that globular clusters are comparable everywhere then indicates that the environments in which they formed were very similar, regardless of the galaxy they currently reside in. Kruijssen and his team says globular clusters can therefore be used to shed more light on how the first generations of stars and galaxies were born.
“In the nearby Universe, there are several examples of galaxies that have recently undergone large bursts of star formation,” said Kruijssen. “It should therefore be possible to see the rapid destruction of small stellar clusters in action. If this is indeed found by new observations, it will confirm our theory for the origin of globular clusters.”
This new finding may also tie in with other recent findings from Spitzer and ESO that starburst activity may have only lasted around 100 million years and may have also been cut short when black holes formed at the center of galaxies.
