galaxies Archives

November 18, 2009December 24, 2015 by Nancy Atkinson

“X” Marks Puzzling Galactic Bulge

Looking at a galaxy edge-on provides astronomers the opportunity to study different aspects of galaxies than a face-on view offers. This Hubble image of NGC 4710 is part of a survey conducted to provide more information about the puzzling bulges that form around the middle of some galaxies. Have these galaxies been “eating” too much, or is it just part of a “middle-age spread” similar to what humans experience? Astronomers aren’t sure why bulges evolve and become a substantial component of most spiral galaxies.

This image was taken by the Advanced Camera for Surveys in 2006, before the recent Hubble Servicing Mission.

A faint, ethereal “X”-shaped structure is also visible. Such a feature, which astronomers call a “boxy” or “peanut-shaped” bulge, is due to the vertical motions of the stars in the galaxy’s bar and is only evident when the galaxy is seen edge-on. This curiously shaped puff is often observed in spiral galaxies with small bulges and open arms, but is less common in spirals with arms tightly wrapped around a more prominent bulge, such as NGC 4710.

Click here to watch a movie zooming into this galaxy.

When targeting spiral galaxy bulges, astronomers often seek edge-on galaxies, as their bulges are more easily distinguishable from the disc. This exceptionally detailed edge-on view of NGC 4710 taken by the Advanced Camera for Surveys (ACS) aboard Hubble reveals the galaxy’s bulge in the brightly coloured centre. The luminous, elongated white plane that runs through the bulge is the galaxy disc. The disc and bulge are surrounded by eerie-looking dust lanes.

A wide-field image of the region around NGC 4710 constructed from Digitized Sky Survey 2 data. The field of view is approximately 2.8 degrees x 2.9 degrees. Credit: NASA, ESA and Digitized Sky Survey 2. Acknowledgment: Davide De Martin (ESA/Hubble)

NGC 4710 is a member of the giant Virgo Cluster of galaxies and lies in the northern constellation of Coma Berenices (the Hair of Queen Berenice). It is not one of the brightest members of the cluster, but can easily be seen as a dim elongated smudge on a dark night with a medium-sized amateur telescope. In the 1780s, William Herschel discovered the galaxy and noted it simply as a “faint nebula”. It lies about 60 million light-years from the Earth and is an example of a lenticular or S0-type galaxy – a type that seems to have some characteristics of both spiral and elliptical galaxies.

Astronomers are scrutinizing these systems to determine how many globular clusters they host. Globular clusters are thought to represent an indication of the processes that can build bulges. Two quite different processes are believed to be at play regarding the formation of bulges in spiral galaxies: either they formed rather rapidly in the early Universe, before the spiral disc and arms formed; or they built up from material accumulating from the disc during a slow and long evolution. In this case of NGC 4710, researchers have spotted very few globular clusters associated with the bulge, indicating that its assembly mainly involved relatively slow processes.

Source: STSci

November 3, 2009December 24, 2015 by Nancy Atkinson

Hints of More Extra-Galactic Planets

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We regularly report on the discovery of extrasolar planets in our galaxy, but earlier this year came news of possibly the first planet discovered outside of the Milky Way. Now comes news of the potential discovery of dozens of extragalactic planetary systems. Erin Mentuch and her colleagues at the University of Toronto in Canada have analyzed 88 remote galaxies and found a broad continuum excess in the near-infrared. They conclude the most likely explanation for the 2-5 micron excess is the light from circumstellar disks, or young solar systems, forming around massive young stars. “[This] presents us with an exciting opportunity to measure the formation rate of planetary systems at cosmic epochs before our own Solar System formed,” the team writes in their paper.

The light from the galaxies studied was emitted when the universe was between a quarter and half its current age – making them far too remote for their stars to be seen individually. The galaxies’ light output peaks at two distinct wavelengths. One represents the combined light of a galaxy’s stars; the other, at longer wavelengths, comes from the glow of its interstellar dust.

In each case, the team noticed a faint third component between the two peaks. Whatever produces this light is too cold to be stars and too warm to be dust. The most likely source is circumstellar discs – embryonic solar systems around young stars. “It’s the most surprising result I’ve ever worked on,” said Roberto Abraham, one of the team members.

The opportunity to study discs that existed so long ago could help reveal how the rate of planet formation across the universe has changed over time, says Mentuch.

Read the team’s paper.

Source: Daily Mail

November 3, 2009December 24, 2015 by Nancy Atkinson

Do “Skeleton” Filaments Give Structure to the Universe?

This 3D illustration shows the position of the galaxies and reveals the extent of this gigantic structure. The galaxies located in the newly discovered structure are shown in red. Galaxies that are either in front or behind the structure are shown in blue. Credit: ESO

Are there “skeletons” out in the Universe –structures that form the framework of how galaxies are distributed? Astronomers have tracked down a gigantic, previously unknown assembly of galaxies located almost seven billion light-years away from us, which seems to point to a prominent galaxy structure in the distant Universe, providing further insight into the cosmic web and how it formed. “Matter is not distributed uniformly in the Universe,” says Masayuki Tanaka from ESO, who led the new study. “In our cosmic vicinity, stars form in galaxies and galaxies usually form groups and clusters of galaxies. The most widely accepted cosmological theories predict that matter also clumps on a larger scale in the so-called ‘cosmic web’, in which galaxies, embedded in filaments stretching between voids, create a gigantic wispy structure.”

The filament is located about 6.7 billion light-years away from us and extends over at least 60 million light-years. The newly uncovered structure does probably extend further, beyond the field probed by the team, and hence future observations have already been planned to obtain a definite measure of its size.

These filaments are millions of light years long and constitute the skeleton of the Universe: galaxies gather around them, and immense galaxy clusters form at their intersections, lurking like giant spiders waiting for more matter to digest. Scientists are struggling to determine how they swirl into existence. Although massive filamentary structures have been often observed at relatively small distances from us, solid proof of their existence in the more distant Universe has been lacking until now.

The galaxies located in the newly discovered structure are shown in red. Galaxies that are either in front or behind the structure are shown in blue. Credit: ESO

The team led by Tanaka discovered a large structure around a distant cluster of galaxies in images they obtained earlier. They have now used two major ground-based telescopes to study this structure in greater detail, measuring the distances from Earth of over 150 galaxies, and, hence, obtaining a three-dimensional view of the structure. The spectroscopic observations were performed using the VIMOS instrument on ESO’s Very Large Telescope and FOCAS on the Subaru Telescope, operated by the National Astronomical Observatory of Japan.

With these and other observations, the astronomers were able to make a real demographic study of this structure, and have identified several groups of galaxies surrounding the main galaxy cluster. They could distinguish tens of such clumps, each typically ten times as massive as our own Milky Way galaxy — and some as much as a thousand times more massive — while they estimate that the mass of the cluster amounts to at least ten thousand times the mass of the Milky Way. Some of the clumps are feeling the fatal gravitational pull of the cluster, and will eventually fall into it.

Image of the assembly of galaxies. Credit: ESO

“This is the first time that we have observed such a rich and prominent structure in the distant Universe,” says Tanaka. “We can now move from demography to sociology and study how the properties of galaxies depend on their environment, at a time when the Universe was only two thirds of its present age.”

Source: ESO

November 2, 2009April 26, 2016 by Nancy Atkinson

Solving the Mystery of Cosmic Rays’ Origins

What accelerates cosmic rays to nearly the speed of light? Astronomer have pondered that question for nearly 100 years, and now new evidence supports a theory held for two decades that cosmic rays likely are powered by exploding stars and stellar winds. “This discovery has been predicted for almost 20 years, but until now no instrument was sensitive enough to see it,” said Wystan Benbow, an astrophysicist at the Smithsonian Astrophysical Observatory who coordinated this project for the Very Energetic Radiation Imaging Telescope Array System (VERITAS) collaboration.

Nearly 100 years ago, scientists detected the first signs of cosmic rays, which are actually not rays or beams but subatomic particles (mostly protons) that zip through space at nearly the speed of light. The most energetic cosmic rays hit with the punch of a 98-mph fastball, even though they are smaller than an atom. Astronomers questioned what natural force could accelerate particles to such a speed.

The rarest cosmic rays carry over 100 billion times as much energy as generated by any particle accelerator on Earth. Astronomers have devised ingenious methods for detecting cosmic rays that hit Earth’s atmosphere. However, detecting cosmic rays from a distance requires much more effort.

This representative-color figure shows the very-high-energy gamma-ray emission observed by VERITAS coming from the Cigar Galaxy, also known as Messier 82. The black star is the location of the active starburst region. The emission from M82 is effectively point-like for VERITAS, and the white circle indicates the size of a simulated point source. The entire galaxy would be contained within the circle. Credit: CfA/V.A. Acciari

VERITAS has found new evidence for cosmic rays in the “Cigar Galaxy,” also known as Messier 82 (M82), which is located 12 million light-years from Earth in the direction of the constellation Ursa Major, which strongly support the long-held theory that supernovae and stellar winds from massive stars are the dominant accelerators of cosmic-ray particles.

Galaxies with high levels of star formation like M82, also known as “starburst” galaxies, have large numbers of supernovae and massive stars. If the theory holds, then starburst galaxies should contain more cosmic rays than normal galaxies. The VERITAS discovery confirms that expectation, indicating that the cosmic-ray density in M82 is approximately 500 times the average density in our Galaxy, the Milky Way.

“This discovery provides fundamental insight into the origin of cosmic rays,” said Rene Ong, a professor of physics at the University of California, Los Angeles, and the spokesperson for the VERITAS collaboration.

Using gamma rays to infer cosmic rays

VERITAS could not detect M82’s cosmic rays directly because they are trapped within the Cigar Galaxy. Instead, VERITAS looked for clues to the presence of cosmic rays: gamma rays. Gamma rays are the most energetic form of light, far more powerful than ultraviolet light or even X-rays. When cosmic rays interact with interstellar gas and radiation within M82, they produce gamma rays, which can then escape their home galaxy and reach Earthbound detectors.

It took two years of dedicated data collection to tease out the faint signal coming from M82.

“We knew that the detection of M82 would have important scientific implications. As a result, we scheduled an exceptionally long exposure immediately after the experiment became fully operational” said Benbow. “The data needed to be meticulously analyzed to extract the gamma-ray signal, which is over a million times smaller than the background noise. Although the signal is only a tiny fraction of the data, we made many checks for possible bias and we are confident that the signal is genuine.”

“The detection of M82 indicates that the universe is full of natural particle accelerators, and as ground-based gamma-ray observatories continue to improve, further discoveries are inevitable.” said Martin Pohl, a professor of physics at Iowa State University who helped lead the study. A next-generation VHE gamma-ray observatory, the Advanced Gamma-ray Imaging System (AGIS), is already under development.

VERITAS is operated by a collaboration of more than 100 scientists from 22 different institutions in the United States, Ireland, England and Canada. Click here for more information on VERITAS.

Lead image caption: A composite of multi-wavelength images of the active galaxy M82 from Hubble, Chandra, and Spitzer. Credit: NASA, ESA, CXC, and JPL-Caltech

Source: Harvard Smithsonian Center for Astrophysics

October 22, 2009December 24, 2015 by Nancy Atkinson

Galaxy Cluster Far, Far Away Smashes Distance Record

JKC041 galaxy cluster. Credit: X-ray: NASA/CXC/INAF/S.Andreon et al Optical: DSS; ESO/VLT

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A galaxy cluster located about 10.2 billion light years from Earth has been discovered by combining data from NASA’s Chandra X-ray Observatory with optical and infrared telescopes. The cluster, JKCS041, is the most distant galaxy cluster yet observed, and we see it as when the Universe was only about a quarter of its present age. The cluster’s distance beats the previous record holder by about a billion light years.

Galaxy clusters are the largest gravitationally bound objects in the Universe. Finding such a large structure at this very early epoch can reveal important information about how the Universe evolved at this crucial stage.

JKCS041 is at the brink of when scientists think galaxy clusters can exist in the early Universe based on how long it should take for them to assemble. Therefore, studying its characteristics – such as composition, mass, and temperature – will reveal more about how the Universe took shape.

“This object is close to the distance limit expected for a galaxy cluster,” said Stefano Andreon of the National Institute for Astrophysics (INAF) in Milan, Italy. “We don’t think gravity can work fast enough to make galaxy clusters much earlier.”

JKCS041 was originally detected in 2006 in a survey from the United Kingdom Infrared Telescope (UKIRT). The distance to the cluster was then determined from optical and infrared observations from UKIRT, the Canada-France-Hawaii telescope in Hawaii and NASA’s Spitzer Space Telescope. Infrared observations are important because the optical light from the galaxies at large distances is shifted into infrared wavelengths because of the expansion of the universe.

The Chandra data were the final – but crucial – piece of evidence as they showed that JKCS041 was, indeed, a genuine galaxy cluster. The extended X-ray emission seen by Chandra shows that hot gas has been detected between the galaxies, as expected for a true galaxy cluster rather than one that has been caught in the act of forming.

Also, without the X-ray observations, the possibility remained that this object could have been a blend of different groups of galaxies along the line of sight, or a filament, a long stream of galaxies and gas, viewed front on. The mass and temperature of the hot gas detected estimated from the Chandra observations rule out both of those alternatives.

The extent and shape of the X-ray emission, along with the lack of a central radio source argue against the possibility that the X-ray emission is caused by scattering of cosmic microwave background light by particles emitting radio waves.

It is not yet possible, with the detection of just one extremely distant galaxy cluster, to test cosmological models, but searches are underway to find other galaxy clusters at extreme distances.

“This discovery is exciting because it is like finding a Tyrannosaurus Rex fossil that is much older than any other known,” said co-author Ben Maughan, from the University of Bristol in the United Kingdom. “One fossil might just fit in with our understanding of dinosaurs, but if you found many more, you would have to start rethinking how dinosaurs evolved. The same is true for galaxy clusters and our understanding of cosmology.”

The previous record holder for a galaxy cluster was 9.2 billion light years away, XMMXCS J2215.9-1738, discovered by ESA’s XMM-Newton in 2006. This broke the previous distance record by only about 0.1 billion light years, while JKCS041 surpasses XMMXCS J2215.9 by about ten times that.

“What’s exciting about this discovery is the astrophysics that can be done with detailed follow-up studies,” said Andreon.

Among the questions scientists hope to address by further studying JKCS041 are: What is the build-up of elements (such as iron) like in such a young object? Are there signs that the cluster is still forming? Do the temperature and X-ray brightness of such a distant cluster relate to its mass in the same simple way as they do for nearby clusters?

Source: EurekAlert

October 14, 2009December 24, 2015 by Nancy Atkinson

Straight From the Island of Misfit Galaxies: Barnard

Barnard’s Galaxy, from the MPG/ESO telescope at ESO’s La Silla Observatory in northern Chile. Credit: ESO

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By galactic standards, Barnard is a misfit. This galaxy is diminutive, oddly shaped, and hard to see. But give the little box-shaped guy credit: this dwarf galaxy has no shortage of stellar splendor and pyrotechnics. Some feisty star formation is taking place, and a few curious nebulae dot the landscape with scorching stars sending waves of matter smashing into the surrounding stellar material. Plus, Barnard has a storied past: it likely was the victim of cannibalization. But cosmic misfits like Barnard’s Galaxy help researchers understand how galaxies interact, evolve and occasionally feed on each other, leaving behind radiant, star-filled scraps.

In this new image from ESO, Barnard’s Galaxy glows beneath a sea of foreground stars in the direction of the constellation of Sagittarius (the Archer). Also known as NGC 6822, the nicknamed comes its discoverer, American astronomer Edward Emerson Barnard, who spied it with his 125-millimeter aperture refractor in 1884. At the relatively close distance of about 1.6 million light-years, Barnard’s Galaxy is a member of the Local Group (ESO 11/96), the archipelago of galaxies that includes our home, the Milky Way.

Astronomers obtained this latest portrait using the Wide Field Imager (WFI) attached to the 2.2-metre MPG/ESO telescope at ESO’s La Silla Observatory in northern Chile.

At only about a tenth of the Milky Way’s size, Barnard’s Galaxy fits its dwarfish classification. All told, it contains about 10 million stars — a far cry from the Milky Way’s estimated 400 billion. In the Local Group, as elsewhere in the Universe, however, dwarf galaxies outnumber their larger, shapelier cousins, such as the Milky Way, the Andromeda and the Triangulum galaxies.

Even though Barnard’s Galaxy lacks the majestic spiral arms and glowing, central bulge that grace its big galactic neighbors, the Milky Way, the Andromeda and the Triangulum galaxies, there is a lot going on in this dwarf galaxy.

Reddish nebulae in this image reveal regions of active star formation, where young, hot stars heat up nearby gas clouds. Also prominent in the upper left of this new image is a striking bubble-shaped nebula. At the nebula’s centre, a clutch of massive, scorching stars send waves of matter smashing into the surrounding interstellar material, generating a glowing structure that appears ring-like from our perspective. Other similar ripples of heated matter thrown out by feisty young stars are dotted across Barnard’s Galaxy.

Irregular dwarf galaxies like Barnard’s Galaxy get their random, blob-like forms from close encounters with or “digestion” by other galaxies. Like everything else in the Universe, galaxies are in motion, and they often make close passes or even go through one another. The density of stars in galaxies is quite low, meaning that few stars physically collide during these cosmic dust-ups. Gravity’s fatal attraction, however, can dramatically warp and scramble the shapes of the passing or crashing galaxies. Groups of stars are pulled or flung from their galactic home, in turn forming irregularly shaped dwarf galaxies like NGC 6822.

Click here to see a zoom-in video (choose from various formats) of Barnard’s Galaxy.

The image was made from data obtained through four different filters (B, V, R, and H-alpha). The field of view is 35 x 34 arcmin. North is up, East to the left.

Source: ESO

October 13, 2009April 26, 2016 by Nancy Atkinson

New Hubble Release: Dramatic Galaxy Collision

NGC 2623, or Arp 243, is about 250 million light-years away in the constellation of Cancer (the Crab). Image credit: NASA, ESA and A. Evans (Stony Brook University, New York & National Radio Astronomy Observatory, Charlottesville, USA)

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At first glance, this latest image release from Hubble appears to be one really bizarre-looking galaxy. But actually, this is a pair of spiral galaxies that resemble our own Milky Way smashing together at breakneck speeds. The centers have already merged into one nucleus, and the two tidal tails stretching out from the center are sparkling with active star formation, prompted by the exchange of mass and gases from the dramatic collision. This object, NGC 2623, or Arp 243, is about 250 million light-years away in the constellation of Cancer (the Crab), and is in the late stages of the merging process.

The prominent lower tail is richly populated with bright star clusters — 100 of them have been found in these observations. The large star clusters that the team has observed in the merged galaxy are brighter than the brightest clusters we see in our own vicinity. These star clusters may have formed as part of a loop of stretched material associated with the northern tail, or they may have formed from debris falling back onto the nucleus. In addition to this active star-forming region, both galactic arms harbor very young stars in the early stages of their evolutionary journey.

Watch this video for more information on NGC 2623:

Some mergers (including NGC 2623) can result in an active galactic nucleus, where one of the supermassive black holes found at the centers of the two original galaxies is stirred into action. Matter is pulled toward the black hole, forming an accretion disc. The energy released by the frenzied motion heats up the disc, causing it to emit across a wide swath of the electromagnetic spectrum.

NGC 2623 is so bright in the infrared that it belongs to the group of very luminous infrared galaxies (LIRG) and has been extensively studied as the part of the Great Observatories All-sky LIRG Survey (GOALS) project that combines data from Hubble, the Spitzer Space Telescope, Chandra X-ray Observatory and the Galaxy Evolution Explorer (GALEX). The combination of resources is helping astronomers characterize objects like active galactic nuclei and nuclear star formation by revealing what is unseen at visible wavelengths.

The data used for this color composite were actually taken in 2007 by the Advanced Camera for Surveys (ACS) aboard Hubble, but is just being released now, as a team of over 30 astronomers, led by Aaron S. Evans, recently published an overview paper, detailing the first results of the GOALS project. Observations from ESA’s X-ray Multi-Mirror Mission (XMM-Newton) telescope contributed to the astronomers’ understanding of NGC 2623.

NGC 2623 paper
GOALS Overview paper
GOALS website

Source: European Hubble website

September 30, 2009December 24, 2015 by Nancy Atkinson

Hubble Sees Galaxies Stripped by Ram Pressure

This composite shows the two ram pressure stripping galaxies NGC 4522 and NGC 4402. Credit: NASA & ESA

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Strange forces of nature are stripping away gas from galaxies in the Virgo cluster. An extremely hot X-ray emitting gas known as the intra-cluster medium permeates the regions between galaxies inside clusters and, as fast moving galaxies whip through this medium, strong winds tear through galaxies distorting their shape and even halting star formation with a process known as “ram pressure stripping.” Hubble spied two galaxies “losing it” to these forces.

Ram pressure is the drag force that results when something moves through a fluid — much like the wind you feel in your face when bicycling, even on a still day — and occurs in this context as galaxies orbiting about the centre of the cluster move through the intra-cluster medium, which then sweeps out gas from within the galaxies.

The two galaxies — NGC 4522 and NGC 4402 – were imaged by the old Advanced Camera for Surveys on Hubble before it suffered from a power failure in 2007. Astronauts on Servicing Mission 4 in May 2009 were able to restore ACS during their 13-day mission.

This image shows NGC 4522 within the context of the Virgo Cluster. Credit: NASA, ESA and the Digitized Sky Survey 2. Acknowledgment: Davide De Martin (ESA/Hubble)

The spiral galaxy NGC 4522 is located some 60 million light-years away from Earth and it is a spectacular example of a spiral galaxy currently being stripped of its gas content. Astronomers estimate the galaxy is moving at more than 10 million kilometers per hour, and its rapid motion within the cluster results in strong winds across the galaxy as the gas within is left behind. A number of newly formed star clusters that developed in the stripped gas can be seen in the Hubble image.

The image provides a vivid view of the ghostly gas being forced out of it. Bright blue pockets of new star formation can be seen to the right and left of centre. The image is sufficiently deep to show distant background galaxies.

The image of NGC 4402 also highlights some telltale signs of ram pressure stripping such as the curved, or convex, appearance of the disc of gas and dust, a result of the forces exerted by the heated gas. Light being emitted by the disc backlights the swirling dust that is being swept out by the gas. Studying ram pressure stripping helps astronomers better understand the mechanisms that drive the evolution of galaxies, and how the rate of star formation is suppressed in very dense regions of the Universe like clusters.

Source: Hubble Science Center

September 16, 2009December 24, 2015 by Nancy Atkinson

Best Ever View of Andromeda in Ultraviolet

Andromeda by the Swift Telescope. Credit: NASA/Swift/Stefan Immler (GSFC) and Erin Grand (UMCP)

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Normally, the Swift satellite is searching for distant cosmic explosions. But recently it took some time to take a long look (total exposure time: 24 hours) with its ultraviolet eyes at the Andromeda galaxy, a.k.a. M31. The result is this gorgeous image. “Swift reveals about 20,000 ultraviolet sources in M31, especially hot, young stars and dense star clusters,” said Stefan Immler, a research scientist on the Swift team at NASA’s Goddard Space Flight Center. “Of particular importance is that we have covered the galaxy in three ultraviolet filters. That will let us study M31’s star-formation processes in much greater detail than previously possible.”

Compare this image to an optical version taken by a ground-based telescope:

Andromeda. Credit: Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF

M31, also known as the Andromeda Galaxy, is more than 220,000 light-years across and lies 2.5 million light-years away. On a clear, dark night, the galaxy is faintly visible as a misty patch to the naked eye.

Between May 25 and July 26, 2008, Swift’s Ultraviolet/Optical Telescope (UVOT) acquired 330 images of M31 at wavelengths of 192.8, 224.6, and 260 nanometers.

“Swift is surveying nearby galaxies like M31 so astronomers can better understand star- formation conditions and relate them to conditions in the distant galaxies where we see gamma-ray bursts occurring,” said Neil Gehrels, the mission’s principal investigator. Since Swift’s November 2005 launch, the satellite has detected more than 400 gamma-ray bursts — massive, far-off explosions likely associated with the births of black holes.

For more info on this image see this page from NASA. There’s also a podcast from Swift about this image, as well.

September 3, 2009December 24, 2015 by Nancy Atkinson

Andromeda Galaxy Eating the Neighborhood

An artist's rendering shows the spiral galaxy of Andromeda, center right, over a period of about three billion years as repeated, but modified views of the dwarf galaxy Triangulum, move away from it, clockwise towards Earth, then back towards it, where Triangulum will be ultimately devoured by the Andromeda galaxy says astronomer John Dubinski. (AP Photo/Illustration by John Dubinski and Larry Widrow)

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From Earth, the Andromeda Galaxy looks like a calm, bright galaxy, and is visible with the naked eye in our night sky. But astronomers have discovered things aren’t as tranquil as it seems over at M31. Andromeda is eating the neighbors.

The Andromeda Galaxy contains a trillion stars and lies only about 2.5 million light-years away, so it is a great object to observe and study. But recently astronomers observed wispy streams of stars on the outer fringes of Andromeda, and realized they were leftovers from a cannibalistic feeding frenzy of smaller galaxies it has absorbed.

“This is a startling visual demonstration of the truly vast scale of galaxies,” said Dr. Mike Irwin from the University of Cambridge. “The survey has produced an unrivalled panorama of galaxy structure which reveals that galaxies are the result of an ongoing process of accretion and interaction with their neighbours.”

The cannibalism continues and another victim lies in wait: M33 in the constellation of Triangulum, is destined for a future meal.

“Ultimately, these two galaxies may end up merging completely,” Dr. Scott also from the University of Cambridge. “Ironically, galaxy formation and galaxy destruction seem to go hand in hand.”

Astronomers from Cambridge were part of an international team that made a million light-year-wide survey of the Andromeda Galaxy and its surroundings using a powerful digital camera on the giant Canada-France-Hawaii telescope on Mauna Kea, Hawaii.

They discovered that many of these stars could not have formed within Andromeda itself because the density of gas so far from the galaxy’s core would have been too low to allow formation to take place. Therefore, the team reason that they are almost certainly the remnants of other, smaller galaxies which have been absorbed by Andromeda – and that Andromeda itself is still in a state of expansion.

The team’s paper argues that the larger-scale substructures identified on the galaxy’s fringes are probably the “undigested” remains of previously accreted dwarf galaxies. In all likelihood, they originally belonged to dwarf galaxies or other, proto-galactic fragments.

Article in Nature.

Source: PhysOrg