Astronomers solve puzzle about bizarre object at the center of our galaxy

Telescopes from Hawaii's W.M. Keck Observatory use a powerful technology called adaptive optics, which enabled UCLA astronomers to discover that G2 is a pair of binary stars that merged together, cloaked in gas and dust. 

Credit: Ethan Tweedie

For years, astronomers have been puzzled by a bizarre object in the center of the Milky Way that was believed to be a hydrogen gas cloud headed toward our galaxy's enormous black hole.

Having studied it during its closest approach to the black hole this summer, UCLA astronomers believe that they have solved the riddle of the object widely known as G2.

A team led by Andrea Ghez, professor of physics and astronomy in the UCLA College, determined that G2 is most likely a pair of binary stars that had been orbiting the black hole in tandem and merged together into an extremely large star, cloaked in gas and dust, its movements choreographed by the black hole's powerful gravitational field.

The research is published today in the journal Astrophysical Journal Letters.

Astronomers had figured that if G2 had been a hydrogen cloud, it could have been torn apart by the black hole, and that the resulting celestial fireworks would have dramatically changed the state of the black hole.

"G2 survived and continued happily on its orbit; a simple gas cloud would not have done that," said Ghez, who holds the Lauren B. Leichtman and Arthur E. Levine Chair in Astrophysics. "G2 was basically unaffected by the black hole. There were no fireworks."

Black holes, which form out of the collapse of matter, have such high density that nothing can escape their gravitational pull, not even light.

They cannot be seen directly, but their influence on nearby stars is visible and provides a signature, said Ghez, a 2008 MacArthur Fellow.

Ghez, who studies thousands of stars in the neighborhood of the supermassive black hole, said G2 appears to be just one of an emerging class of stars near the black hole that are created because the black hole's powerful gravity drives binary stars to merge into one.

She also noted that, in our galaxy, massive stars primarily come in pairs. She says the star suffered an abrasion to its outer layer but otherwise will be fine.

Ghez and her colleagues, who include lead author Gunther Witzel, a UCLA postdoctoral scholar, and Mark Morris and Eric Becklin, both UCLA professors of physics and astronomy, conducted the research at Hawaii's W.M. Keck Observatory, which houses the world's two largest optical and infrared telescopes.

When two stars near the black hole merge into one, the star expands for more than 1 million years before it settles back down, said Ghez, who directs the UCLA Galactic Center Group. "This may be happening more than we thought.

The stars at the center of the galaxy are massive and mostly binaries. It's possible that many of the stars we've been watching and not understanding may be the end product of mergers that are calm now."

Ghez and her colleagues also determined that G2 appears to be in that inflated stage now. The body has fascinated many astronomers in recent years, particularly during the year leading up to its approach to the black hole.

"It was one of the most watched events in astronomy in my career," Ghez said.

Ghez said G2 now is undergoing what she calls a "spaghetti-fication", a common phenomenon near black holes in which large objects become elongated.

At the same time, the gas at G2's surface is being heated by stars around it, creating an enormous cloud of gas and dust that has shrouded most of the massive star.

Witzel said the researchers wouldn't have been able to arrive at their conclusions without the Keck's advanced technology.

"It is a result that in its precision was possible only with these incredible tools, the Keck Observatory's 10-meter telescopes," Witzel said.

The telescopes use adaptive optics, a powerful technology pioneered in part by Ghez that corrects the distorting effects of the Earth's atmosphere in real time to more clearly reveal the space around the supermassive black hole.

The technique has helped Ghez and her colleagues elucidate many previously unexplained facets of the environments surrounding supermassive black holes.

"We are seeing phenomena about black holes that you can't watch anywhere else in the universe," Ghez added.

"We are starting to understand the physics of black holes in a way that has never been possible before."

More information: Astrophysical Journal Letters, iopscience.iop.org/2041-8205/796/1/L8/article

Mysterious signal detected in galaxy 240 million light years away

Astronomers have detected a mysterious signal 240 million light years away from Earth. The unidentified signal is a 'spike of intensity at a very specific wavelength of x-ray light', but scientists don't yet know what the origin is.

Picked up in the Perseus Cluster, one of the biggest objects in the universe, the discovery is said to be the best evidence of dark matter yet.

Astronomers believe dark matter constitutes 85 per cent of the matter in the universe, but doesn't emit or absorb light like normal matter such as protons or electrons, which are known to make up the familiar elements seen in planets, stars, and galaxies.

Researchers suggest intensity coming from the Perseus Cluster could be a signature from the decay of a 'sterile neutrino,' which are a hypothetical type of neutrino thought to interact with normal matter via gravity but while holding exciting potential, the results must be confirmed with additional data to rule out other explanations and to see whether it is plausible that dark matter has been observed.

ESA XMM-Newton: Unique pair of supermassive black holes discovered

Artist’s impression of a pair of black holes. 

One of them is accreting the 'debris' of the disrupted star, while the second is temporarily interrupting the stream of gas toward the other black hole. 

Credit: ESA /C. Carreau

A pair of supermassive black holes in orbit around one another have been discovered by an international research team including Stefanie Komossa from the Max Planck Institute for Radio Astronomy in Bonn, Germany. This is the first time such a pair could be found in an ordinary galaxy.

Stefanie Komossa

They were discovered because they ripped apart a star when ESA's space observatory XMM-Newton happened to be looking in their direction.

The findings are published in the May 10 issue of the Astrophysical Journal, and appeared online today at the astrophysics preprint server.

Most massive galaxies in the universe are thought to harbor at least one supermassive black hole at their center.

Two supermassive black holes are the smoking gun that the galaxy has merged with another.

Thus, finding binary supermassive black holes can tell astronomers about how galaxies evolved into their present-day shapes and sizes.

To date, only a few candidates for close binary supermassive black holes have been found. All are in active galaxies where they are constantly ripping gas clouds apart, in the prelude to crushing them out of existence.

In the process of destruction, the gas is heated so much that it shines at many wavelengths, including X-rays. This gives the galaxy an unusually bright center, and leads to it being called active.

Fukun Liu

The new discovery, reported by Fukun Liu from Peking University in China, and colleagues, is important because it is the first to be found in a galaxy that is not active.

"There might be a whole population of quiescent galaxies that host binary black holes in their centers," says co-author Stefanie Komossa, Max-Planck-Institut für Radioastronomie, Bonn, Germany.

But finding them is a difficult task because in quiescent galaxies, there are no gas clouds feeding the black holes, and so the cores of these galaxies are truly dark.

The only hope that the astronomers have is to be looking in the right direction at the moment one of the black holes goes to work, and rips a star to pieces. Such an occurrence is called a 'tidal disruption event.'

As the star is pulled apart by the gravity of the black hole, it gives out a flare of X-rays.

In an active galaxy, the black hole is continuously fed by gas clouds. In a quiescent galaxy, the black hole is fed by tidal disruption events that occur sporadically and are impossible to predict.

So, to increase the chances of catching such an event, researchers use ESA's X-ray observatory, XMM-Newton, in a novel way.

ESA's X-ray observatory, XMM-Newton

Artist's impression of XMM-Newton spacecraft in orbit around the Earth. 

The X-ray emission from galaxy SDSS J120136.02+300305.5 was detected in slew modus of the space observatory. 

Credit: ESA /D. Ducros

Usually, the observatory collects data from designated targets, one at a time.

Once it completes an observation, it slews to the next.

The trick is that during this movement, XMM-Newton keeps the instruments turned on and recording.

Effectively this surveys the sky in a random pattern, producing data that can be analyzed for unknown or unexpected sources of X-rays.

On 10 June 2010, a tidal disruption event was spotted by XMM-Newton in galaxy SDSS J120136.02+300305.5, approximately 2 billion light-years away.

NASA's Swift satellite

Komossa and her colleagues were scanning the data for such events and scheduled follow-up observations just days later with XMM-Newton and NASA's Swift satellite.

The galaxy was still spilling X-rays into space.

It looked exactly like a tidal disruption event caused by a supermassive black hole but as they tracked the slowly fading emission day after day something strange happened.

The X-rays fell below detectable levels between days 27 and 48 after the discovery. Then they re-appeared and continued to follow a more expected fading rate, as if nothing had happened.

Now, thanks to Fukun Liu, this behaviour can be explained. "This is exactly what you would expect from a pair of supermassive black holes orbiting one another," says Liu.

More information: "A milliparsec supermassive black hole binary candidate in the galaxy SDSS J120136.02+300305.5," by F. K. Liu, Shuo Li, and S. Komossa, 2014, Astrophysical Journal, Volume 786, Article 103 (May 10). DOI: 10.1088/0004-637X/786/2/103 . Preprint: arxiv.org/abs/1404.4933

Green Bank Telescope: Hidden details revealed in nearby starburst galaxy

This composite image of starburst galaxy M82 shows the distribution of dense molecular gas as seen by the GBT (yellow and red) and the background stars and dust as seen by the Hubble Space telescope (blue).

The yellow areas correspond to regions of intense star formation.

The red areas trace outflows of gas from the disk of the galaxy. 

Credit: Bill Saxton (NRAO/AUI/NSF); Hubble/NASA

Using the new, high-frequency capabilities of the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT), astronomers have captured never-before-seen details of the nearby starburst galaxy M82.

These new data highlight streamers of material fleeing the disk of the galaxy as well as concentrations of dense molecular gas surrounding pockets of intense star formation.

M82, which is located approximately 12 million light-years away in the constellation Ursa Major, is a classic example of a starburst galaxy—one that is producing new stars tens- to hundreds-of-times faster than our own Milky Way.

Its relatively nearby location made it an ideal target for the GBT's newly equipped "W-Band" receiver, which is capable of detecting the millimeter wavelength light that is emitted by molecular gas.

This new capability makes the GBT the world's largest single-dish, millimeter-wave telescope.

Amanda Kepley

"With this new vision, we were able to look at M82 to explore how the distribution of molecular gas in the galaxy corresponded to areas of intense star formation," said Amanda Kepley, a post-doctoral fellow at the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, and lead author on a paper accepted for publication in the Astrophysical Journal Letters.

"Having this new capability may help us understand why stars form where they do."

Astronomers recognize that dense molecular gas goes hand-in-hand with areas of star formation, but the connection is poorly understood and this relationship may be different in different types of galaxies.

By creating wide-angle maps of the gas in galaxies, astronomers hope to better understand this complex interplay.

To date, however, these kinds of observations have not been easy since molecules that are used to map the distribution of dense gas, like HCN (hydrogen cyanide) and HCO+ (formylium), shine feebly in millimeter light.

With its new W-Band receiver, the GBT was able to make highly sensitive, wide-angle images of these gases in and around M82.

"The GBT data clearly show billowing concentrations of dense molecular gas huddled around areas that are undergoing bursts of intense star formation," said Kepley.

"They also reveal giant outflows of ionized gas fleeing the disk of the galaxy. These outflows are driven by star formation deep within the galaxy."

This capability will enable astronomers to quickly survey entire galaxies and different parts within galaxies.

Such surveys would complement higher resolution observations with new Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile.

The 100-meter GBT is located in the National Radio Quiet Zone and the West Virginia Radio Astronomy Zone, which protect the incredibly sensitive telescope from unwanted radio interference.

NRAO VLA: Surprising image provides new tool for studying galaxy

The edge-on spiral galaxy UGC 10288 (horizontal) appeared to be a single object in previous radio telescope observations. 

However, new, detailed radio data (cyan in this image) from the NRAO's VLA reveals that the large perpendicular (vertical) extension really is a distant background galaxy with radio jets.

The foreground image of UGC 10288 includes data from optical, infrared and radio telescopes.

Astronomers studying gas halos around nearby galaxies were surprised when detailed studies with the National Science Foundation's Karl G. Jansky Very Large Array (VLA) showed that one of their subjects is not a single galaxy, but rather two, nearly perfectly superimposed on the sky to masquerade as one.

The discovery allowed them to use the alignment to learn otherwise-unobtainable facts about the nearer galaxy.

As part of a study of 35 galaxies, the astronomers observed one called UGC 10288, a spiral galaxy more than 100 million light-years distant that appears edge-on as seen from Earth.

Their multiple VLA observations in 2011 and 2012 produced the best radio-telescope images of that galaxy ever made.

The detailed images surprisingly revealed a more-distant galaxy, with strong radio emission, almost directly behind UGC 10288. In previous images, the two galaxies had been blended together.

The background galaxy is nearly 7 billion light-years from Earth.

"This changed the picture, quite literally," said Judith Irwin, of Queen's University in Ontario, Canada.

"It changed our understanding of the characteristics of UGC 10288, but also gave us an unexpected new tool for learning more about that galaxy," Irwin added.

The alignment of a foreground galaxy with such a strongly-emitting background galaxy with extended jets probably is the first such alignment found, the astronomers said.

The first insight gleaned from the improved images was that UGC 10288 is not forming stars as rapidly as the astronomers first thought.

This is because much of the radio emission in the previous, blended images came from the background galaxy.

The new images also showed that the gas in the galaxy's "outskirts," high above its spiral disk of stars, is not a single, smooth halo-like envelope, but instead forms smaller, discrete features.

One of these features is arc-like, rising more than 11,000 light-years above the disk.

The background galaxy, and the fact that it is aligned with its radio jets perpendicular to UGC 10288's disk, provides a valuable means of studying the nearer galaxy.

"We can use the radio waves from the background galaxy, coming through the nearer one, as a way to measure the properties of the nearer galaxy," said Jayanne English, of the University of Manitoba.

Preliminary use of the more-distant galaxy in this manner has given the scientists some magnetic-field measurements of different portions of UGC 10288.

The researchers plan to do additional analysis of their data to make more such measurements.

"We're getting a nice scientific reward from the unexpected discovery of the background galaxy," Irwin said.

"Ironically, we would not have included UGC 10288 in our original study if its radio brightness had not been boosted by the background galaxy in the earlier images," she added.

Irwin and English worked with an international team of astronomers from North America, Europe, and India who are part of the Continuum Halos in Nearby Galaxies—an EVLA Survey (CHANG-ES) consortium.

The scientists reported their findings in the Astronomical Journal.

Hubble and Keck: Most Distant Galaxy (so far) revealed

z8_GND_5296 is churning out stars at a remarkable rate, say astronomers

An international team of astronomers has detected the most distant galaxy yet.

The galaxy is about 30 billion light-years away and is helping scientists shed light on the period that immediately followed the Big Bang.

It was found using the Hubble Space Telescope and its distance was then confirmed with the ground-based Keck Observatory in Hawaii.

The study is published in the journal Nature.

Because it takes light so long to travel from the outer edge of the Universe to us, the galaxy appears as it was 13.1 billion years ago (its distance from Earth of 30 billion light-years is because the Universe is expanding).

Steven Finkelstein

Lead researcher Steven Finkelstein, from the University of Texas at Austin, US, said: "This is the most distant galaxy we've confirmed. We are seeing this galaxy as it was 700 million years after the Big Bang."

The far-off galaxy goes by the catchy name of z8_GND_5296.

Astronomers were able to measure how far it was from Earth by analysing its colour.

Because the Universe is expanding and everything is moving away from us, light waves are stretched. This makes objects look redder than they actually are.

Astronomers rate this apparent colour-change on a scale that is called redshift.

They found that this galaxy has a redshift of 7.51, beating the previous record-holder, which had a redshift of 7.21.

This makes it the most distant galaxy ever found.

The system is small: about 1-2% the mass of the Milky Way and is rich in heavier elements.

But it has a surprising feature: it is turning gas and dust into new stars at a remarkable rate, churning them out hundreds of times faster than our own galaxy can.

It is the second far-flung galaxy known that has been found to have a high star-production rate.

Prof Finkelstein said: "One very interesting way to learn about the Universe is to study these outliers and that tells us something about what sort of physical processes are dominating galaxy formation and galaxy evolution.

"What was great about this galaxy is not only is it so distant, it is also pretty exceptional."

He added that in the coming years, astronomers are likely to discover even more distant galaxies when Nasa's James Webb Space Telescope (JWST) is launched and other ground-based telescopes come online.

Powerful jets discovered blowing material out of galaxy

Radio-Telescope Image of the galaxy 4C12.50, nearly 1.5 billion light-years from Earth. 

Inset shows detail of location at end of superfast jet of particles, where a massive gas cloud (yellow-orange) is being pushed by the jet. 

Credit: Morganti et al., NRAO /AUI /NSF

Astronomers using a worldwide network of radio telescopes have found strong evidence that a powerful jet of material propelled to nearly light speed by a galaxy's central black hole is blowing massive amounts of gas out of the galaxy.

This process, they said, is limiting the growth of the black hole and the rate of star formation in the galaxy, and thus is a key to understanding how galaxies develop.

Astronomers have theorized that many galaxies should be more massive and have more stars than is actually the case.

Scientists proposed two major mechanisms that would slow or halt the process of mass growth and star formation -- violent stellar winds from bursts of star formation and pushback from the jets powered by the galaxy's central, supermassive black hole.

Raffaella Morganti

"With the finely-detailed images provided by an intercontinental combination of radio telescopes, we have been able to see massive clumps of cold gas being pushed away from the galaxy's center by the black-hole-powered jets," said Raffaella Morganti, of the Netherlands Institute for Radio Astronomy and the University of Groningen.

The scientists studied a galaxy called 4C12.50, nearly 1.5 billion light-years from Earth. They chose this galaxy because it is at a stage where the black-hole "engine" that produces the jets is just turning on.

As the black hole, a concentration of mass so dense that not even light can escape, pulls material toward it, the material forms a swirling disk surrounding the black hole.

Processes in the disk tap the tremendous gravitational energy of the black hole to propel material outward from the poles of the disk.

At the ends of both jets, the researchers found clumps of hydrogen gas moving outward from the galaxy at 1,000 kilometers per second.

One of the clouds has much as 16,000 times the mass of the Sun, while the other contains 140,000 times the mass of the Sun. The larger cloud, the scientists said, is roughly 160 by 190 light-years in size.

"This is the most definitive evidence yet for an interaction between the swift-moving jet of such a galaxy and a dense interstellar gas cloud," Morganti said.

"We believe we are seeing in action the process by which an active, central engine can remove gas -- the raw material for star formation -- from a young galaxy," she added.

The scientists also said their observations indicate that the jets from the galaxy's core can stretch and deform clouds of interstellar gas to expand their "pushing" effect beyond the narrow width of the jets themselves.

In addition, they reported that, at 4C12.50's stage of development, the jets may turn on and off and so periodically repeat the process of removing gas from the galaxy.

In July, another team of scientists, using the Atacama Large Millimeter/submillimeter Array (ALMA), announced they had found gas being blown from a more-nearby galaxy, called NGC 253, by an intense burst of star formation.

"Both processes are thought to be at work, often simultaneously, in young galaxies to regulate the growth of their central black holes as well as the rate at which they can form new stars," Morganti said.

Morganti and her team used radio telescopes in Europe and the U.S., combining their signals to make one giant, intercontinental telescope.

Journal Reference:
R. Morganti, J. Fogasy, Z. Paragi, T. Oosterloo, M. Orienti. Radio Jets Clearing the Way Through a Galaxy: Watching Feedback in Action. Science, 2013; 341 (6150): 1082 DOI: 10.1126/science.1240436

GRB Explosion illuminates invisible galaxy in the dark ages

Before light from the gamma-ray burst arrives at the Earth for astronomers to study, it passes through interstellar gas in its host galaxy (close-up view, left), and intergalactic gas between the distant galaxy and us (wide view, right).

This gas filters the light by absorbing some colors and leaves a signature on the light that can be seen in its spectrum.

This "signature" allows scientists to characterize the gamma-ray burst, its environment, and the material between us and the distant galaxy.

Credit: Gemini Observatory/AURA, artwork by Lynette Cook

More than 12 billion years ago a star exploded, ripping itself apart and blasting its remains outward in twin jets at nearly the speed of light. At its death it glowed so brightly that it outshone its entire galaxy by a million times.

This brilliant flash traveled across space for 12.7 billion years to a planet that hadn't even existed at the time of the explosion - our Earth.

By analyzing this light, astronomers learned about a galaxy that was otherwise too small, faint and far away for even the Hubble Space Telescope to see.

Ryan Chornock

"This star lived at a very interesting time, the so-called dark ages just a billion years after the Big Bang," says lead author Ryan Chornock of the Harvard-Smithsonian Center for Astrophysics (CfA).

"In a sense, we're forensic scientists investigating the death of a star and the life of a galaxy in the earliest phases of cosmic time," he adds.

The star announced its death with a flash of gamma rays, an event known as a gamma-ray burst (GRB).

GRB 130606A was classified as a long GRB since the burst lasted for more than four minutes.

It was detected by NASA's Swift spacecraft on June 6th. Chornock and his team quickly organized follow-up observations by the MMT Telescope in Arizona and the Gemini North telescope in Hawaii.

"We were able to get right on target in a matter of hours," Chornock says. "That speed was crucial in detecting and studying the afterglow."

A GRB afterglow occurs when jets from the burst slam into surrounding gas, sweeping that material up like a snowplow, heating it, and causing it to glow.

As the afterglow's light travels through the dead star's host galaxy, it passes through clouds of interstellar gas.

Chemical elements within those clouds absorb light at certain wavelengths, leaving "fingerprints." By splitting the light into a rainbow spectrum, astronomers can study those fingerprints and learn what gases the distant galaxy contained.

All chemical elements heavier than hydrogen, helium, and lithium had to be created by stars.

As a result those heavy elements, which astronomers collectively call "metals," took time to accumulate. Life could not have existed in the early universe because the elements of life, including carbon and oxygen, did not exist.

Chornock and his colleagues found that the GRB galaxy contained only about one-tenth of the metals in our solar system. Theory suggests that although rocky planets might have been able to form, life probably could not thrive yet.

"At the time this star died, the universe was still getting ready for life. It didn't have life yet, but was building the required elements," says Chornock.

At a redshift of 5.9, or a distance of 12.7 billion light-years, GRB 130606A is one of the most distant gamma-ray bursts ever found.

"In the future we will be able to find and exploit even more distant GRBs with the planned Giant Magellan Telescope," says Edo Berger of the CfA, a co-author on the publication.

ESA Herschel: Shining a light on cool pools of gas in the galaxy

This illustration shows a newfound reservoir of stellar fuel discovered by the Herschel space observatory (red). 

Credit: ESA/NASA/JPL-Caltech

Newly formed stars shine brightly, practically crying out, "Hey, look at me!" But not everything in our Milky Way galaxy is easy to see.

The bulk of material between the stars in the galaxy -- the cool hydrogen gas from which stars spring -- is nearly impossible to find.

A new study from the Hershel Space Observatory, a European Space Agency mission with important NASA participation, is shining a light on these hidden pools of gas, revealing their whereabouts and quantities.

In the same way that dyes are used to visualize swirling motions of transparent fluids, the Herschel team has used a new tracer to map the invisible hydrogen gas.

The discovery reveals that the reservoir of raw material for making stars had been underestimated before -- almost by one third -- and extends farther out from our galaxy's center than known before.

Jorge Pineda

"There is an enormous additional reservoir of material available to form new stars that we couldn't identify before," said Jorge Pineda of NASA's Jet Propulsion Laboratory, Pasadena, Calif., lead author of a new paper on the findings published in the journal Astronomy and Astrophysics.

"We had to go to space to solve this mystery because our atmosphere absorbs the specific radiation we wanted to detect," said William Langer of JPL, principal investigator of the Herschel project to map the gas.

"We also needed to see far-infrared light to pinpoint the location of the gas. For both these reasons, Herschel was the only telescope for the job."

Stars are created from clouds of gas, made of hydrogen molecules. The first step in making a star is to squeeze gas together enough that atoms fuse into molecules.

William Langer

The gas starts out sparse but, through the pull of gravity and sometimes other constricting forces, it collects and becomes denser.

When the hydrogen gets dense enough, nuclear fusion takes place and a star is born, shining with starlight.

Astronomers studying stars want to follow this journey, from a star's humble beginnings as a cloud of molecules to a full-blown blazing orb.

To do so requires mapping the distribution of the stellar hydrogen fuel across the galaxy.

Unfortunately, most hydrogen molecules in space are too cold to give off any visible light. They lurk unseen by most telescopes.

For decades, researchers have turned to a tracer molecule called carbon monoxide, which goes hand-in-hand with the hydrogen molecules, revealing their location, but this method has limitations.

In regions where the gas is just beginning to pool -- the earliest stage of cloud formation -- there is no carbon monoxide.

"Ultraviolet light destroys the carbon monoxide," said Langer. "In the space between stars, where the gas is very thin, there is not enough dust to shield molecules from destruction by ultraviolet light."

A different tracer -- ionized carbon -- does, however, linger in these large but relatively empty spaces, and can be used to pin down the hydrogen molecules.

Researchers have observed ionized carbon from space before, but Herschel has, for the first time, provided a dramatically improved geographic map of its location and abundance in the galaxy.

"Thanks to Herschel's incredible sensitivity, we can separate material moving at different speeds," said Paul Goldsmith, a co-author and the NASA Herschel Project Scientist at JPL. "We finally can get the whole picture of what's available to make future generations of stars."

Read a more in-depth story about this research from the European Space Agency at http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=51909 .

The technical paper is online at http://arxiv.org/abs/1304.7770

Galaxy in Throes of Death Spied for 1st Time

Astronomers believe a bright dwarf galaxy relatively close to Earth’s Milky Way and trailing fireballs is the first clear example of a galaxy in the act of dying. 

The galaxy, in the Virgo Cluster, is called IC3418.

CREDIT: Yale

A galaxy has been observed in its cosmic death-throes for the first time.

New research shows that a bright dwarf galaxy in a cluster near the Milky Way is losing its gas, creating a tail of fireballs expelled from the innards of the galaxy.

The galaxy, called IC 3418, appears to be moving from one phase of galactic evolution into another.

"We think we're witnessing a critical stage in the transformation of a gas-rich dwarf irregular galaxy into a gas-poor dwarf elliptical galaxy — the depletion of its lifeblood," the principal investigator of the study, Jeffrey Kenney of Yale University, said in a statement.

"Until now, there has been no clear example of this transformation happening."

IC 3418 is located in the Virgo Cluster — a group of about 1,000 galaxies and the cluster closest to the Milky Way's Local Group of galaxies.

Scientists think that IC 3418 stopped making new stars about 200 to 300 million years ago, rendering the galaxy effectively infertile, the researchers said. "Stars, planets, and life can form only if a galaxy has gas to make them," Kenney said.

The galaxy's fireball tail, however, does show signs of new star formation. The gas within IC 3418 is forced outside of the galaxy by pressure given off by other galaxies in the cluster.

"If you hold popcorn and unpopped kernels of corn in your hand and stick it out the car window as you drive, the wind caused by the car’s motion through the air will blow away the popcorn but leave the denser unpopped kernels in your hand," Kenney said.

"This is like the gas clouds in galaxies being blown out of the galaxy by the wind of cluster gas, while the denser stars remain behind."

Gas cloud reveals Black Holes near centre of Milky Way galaxy

Colour composite image of Centaurus A, revealing the lobes and jets emanating from the active galaxy’s central black hole. 

Composite images: ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray)

A team of researchers from Columbia University has published a paper in Physical Review Letters in which they suggest that the movement of gas cloud G2 near the center of our galaxy may reveal previously hidden small black holes.

They note also that observation of G2's movement might lead to direct evidence of the existence of intermediate size black holes.

G2, a massive cloud of gasses three times the size of Pluto's orbit (but just 3 times the mass of Earth) was discovered moving through our galaxy two years ago by researchers at the Max Planck Institute.

After noting its projected path, the researchers at Columbia have found that it will likely pass through a region of space that is thought to harbor as many as 20,000 small black holes (a single massive black hole is believed to exist at the center of our galaxy.)

They suggest that researchers here on Earth might be able to actually see the interaction between the gas cloud and any black holes that are encountered.

As the gas cloud comes near a black hole, they believe some of the gas will begin to spiral as it's pulled in by its gravity.

That, they say, should cause a lot of heat to be expelled and x-ray light to be emitted—enough to be observable using x-ray telescopes.

They go so far as to estimate that researchers might be able to see evidence of as many as 16 interactions.

More exciting to some in the field, is the possibility that the movement of G2 through our galaxy may give direct evidence of what are known as intermediate sized black holes—believed by some to be several times the mass of our sun.

To date, their existence is purely theoretical. If G2 comes across one, and interacts with it, the event could prove that they really do exist.

They, like the many small black holes in the universe, are believed to reside near the center of the galaxy, which is where G2 is heading.

The researchers estimate it will reach the best position for study this September, giving researchers plenty of time to prepare.

One unknown attribute of G2 could throw a wrench into the project however—the density of the gas cloud is not yet known.

If it's not dense enough, any interactions with a black hole may not create enough light to be seen from Earth.

More information: Gas Cloud G2 Can Illuminate the Black Hole Population Near the Galactic Center, Phys. Rev. Lett. 110, 221102 (2013) prl.aps.org/abstract/PRL/v110/i22/e221102

Abstract
Galactic nuclei are expected to be densely populated with stellar- and intermediate-mass black holes.

Exploring this population will have important consequences for the observation prospects of gravitational waves as well as understanding galactic evolution.

The gas cloud G2 currently approaching Sgr A* provides an unprecedented opportunity to probe the black hole and neutron star population of the Galactic nucleus.

We examine the possibility of a G2-cloud–black-hole encounter and its detectability with current x-ray satellites, such as Chandra and NuSTAR.

We find that multiple encounters are likely to occur close to the pericenter, which may be detectable upon favorable circumstances.

This opportunity provides an additional important science case for leading x-ray observatories to closely follow G2 on its way to the nucleus.

Astronomers Modeling galaxy mergers

An generated optical image of stars in a pair of colliding galaxies after a time of 0.5 billion years, as simulated with a new computer code. 

Credit: P. Hopkins

Astronomers think that many galaxies, including our own Milky Way, have undergone similar collisions during their lifetimes.

Although galaxy collisions are important and common, what happens during these encounters is not very well understood.

For example, it seems likely that massive black hole(s) will form during the interactions, as the two galaxies' nuclei approach each other.

Galaxy-galaxy interactions also stimulate vigorous star formation as gravitational effects during the encounters induce interstellar gas to condense into stars.

The starbursts in turn light up the galaxies, especially at infrared wavelengths, making some systems hundreds or even thousands of times brighter than the Milky Way while the starbursts are underway.

Studying these luminous galaxies not only sheds light on how galaxies evolve and form stars, since they act as lanterns over cosmological distances it also helps scientists study the early universe.

All this impressive progress, however, hinges on an accurate understanding of mergers and how they work.

The general approach is to study many local examples to categorize their behaviors, and then model these cases with computational codes that simulate mergers.

The combination of precise observations and detailed modeling, iteratively applied, helps scientists improve both their understanding of the galaxies and the physical parameters and processes included in the modeling codes.

With these in hand, astronomers can start to probe the more distant universe where the objects are not as easy to measure.

Lars Hernquist

CfA astronomer Lars Hernquist and five of his Harvard colleagues (many of whom were his past students) have now shown that feedback processes from bursts of star formation play a key role in determining how merging galaxies develop, at least when two massive galaxies collide.

Prior models did not fully account for the role played by gas that is driven away by the radiation from a star burst, but which can sometimes fall back the galaxy.

The new paper is particularly effective in describing star formation in the tails and bridges of interacting systems, something had previously been lacking.

NASA Chandra: Black Hole-Powered Jets Collides with nearby Galaxy

Image Credit: NASA

This composite image of a galaxy illustrates how the intense gravity of a supermassive black hole can be tapped to generate immense power. 

The image contains X-ray data from NASA's Chandra X-ray Observatory (blue), optical light obtained with the Hubble Space Telescope (gold) and radio waves from the NSF’s Very Large Array (pink).

This multi-wavelength view shows 4C+29.30, a galaxy located some 850 million light years from Earth. 

The radio emission comes from two jets of particles that are speeding at millions of miles per hour away from a supermassive black hole at the center of the galaxy. 

The estimated mass of the black hole is about 100 million times the mass of our Sun. The ends of the jets show larger areas of radio emission located outside the galaxy.

The X-ray data show a different aspect of this galaxy, tracing the location of hot gas. The bright X-rays in the center of the image mark a pool of million-degree gas around the black hole. 

Some of this material may eventually be consumed by the black hole, and the magnetized, whirlpool of gas near the black hole could in turn, trigger more output to the radio jet.

Most of the low-energy X-rays from the vicinity of the black hole are absorbed by dust and gas, probably in the shape of a giant doughnut around the black hole. 

This doughnut, or torus blocks all the optical light produced near the black hole, so astronomers refer to this type of source as a hidden or buried black hole. 

The optical light seen in the image is from the stars in the galaxy.

The Milky Way Galaxy Viewed over Mount Rainier National Park

The Milky Way Galaxy Viewed over Mount Rainier National Park.

ESA Hubble Image: Sparkling Hook, a nearby starburst galaxy

Credit: ESA Hubble

Visible as a small, sparkling hook in the dark sky, this beautiful object is known as J082354.96 for short.

It is a starburst galaxy, so named because of the incredibly (and unusually) high rate of star formation occurring within it.

One way in which astronomers probe the nature and structure of galaxies like this is by observing the behaviour of their dust and gas components; in particular, the Lyman-alpha emission.

This occurs when electrons within a hydrogen atom fall from a higher energy level to a lower one, emitting light as they do so.

This emission is interesting because this light leaves its host galaxy only after extensive scattering in the nearby gas—meaning that this light can be used as a pretty direct probe of what a galaxy is made up of.

The study of this Lyman-alpha emission is common in very distant galaxies, but now a study named LARS (Lyman Alpha Reference Sample) is investigating the same effect in galaxies that are closer by. The study is published in Astrophysical Journal Letters.

Astronomers chose fourteen galaxies, including this one, and used spectroscopy and imaging to see what was happening within them.

They found that these Lyman-alpha photons can travel much further if a galaxy has less dust—meaning that we can use this emission to infer how dusty the source galaxy is likely to be.

Ring Galaxy Zw II 28: Galaxy With the Hole in the Middle

Galaxy Zw II 28 possesses a mysterious ring shape. 

Researchers believe ring galaxies form when one galaxy slices through the disc of another, larger, one, though without much destruction as might be expected, as galaxies mostly contain empty space. 

This disruption should redistribute the material in both galaxies to form a dense central core, encircled by bright stars, iintensely forming new stars in the outer ring. 

The pink and purple loop of Zw II 28 does not represent a typical ring galaxy due to its lack of a visible central companion. 

However, a companion may lurk just inside the ring. Image released March 11, 2013.

Credit: ESA/Hubble & NASA, Acknowledgement: Judy Schmidt

Youngest-Known Supernova Remnants in the Milky Way Galaxy

G306.3–0.9 in context with star-formation regions in southern Centaurus. Chandra X-ray observations (blue), Spitzer infrared data (red, cyan), and radio observations (purple) from the Australia Telescope Compact Array are merged in this composite.

The image is one degree across, which corresponds to 450 light-years at the remnant's estimated distance. 

Credit: X-ray: NASA/CXC/Univ. of Michigan/M. Reynolds et al; Infrared: NASA/JPL-Caltech; Radio: CSIRO/ATNF/ATCA

While performing an extensive X-ray survey of our galaxy's central regions, NASA's Swift satellite has uncovered the previously unknown remains of a shattered star. The full report here and at NASA Goddard

Designated G306.3-0.9 after the coordinates of its sky position, the new object ranks among the youngest-known supernova remnants in our Milky Way galaxy.

"Astronomers have previously cataloged more than 300 supernova remnants in the galaxy," said lead scientist Mark Reynolds, a postdoctoral researcher at the University of Michigan in Ann Arbor.

"Our analysis indicates that G306.3-0.9 is likely less than 2,500 years old, making it one of the 20 youngest remnants identified."

Astronomers estimate that a supernova explosion occurs once or twice a century in the Milky Way.

The expanding blast wave and hot stellar debris slowly dissipate over hundreds of thousands of years, eventually mixing with and becoming indistinguishable from interstellar gas.

Like fresh evidence at a crime scene, young supernova remnants give astronomers the best opportunity for understanding the nature of the original star and the details of its demise.

Supernova remnants emit energy across the electromagnetic spectrum, from radio to gamma rays, and important clues can be found in each energy band.

X-ray observations figure prominently in revealing the motion of the expanding debris, its chemical content, and its interaction with the interstellar environment, but supernova remnants fade out in X-ray light after 10,000 years.

Indeed, only half of those known in the Milky Way galaxy have been detected in X-rays at all.

Reynolds leads the Swift Galactic Plane Survey, a project to image a two-degree-wide strip along the Milky Way's central plane at X-ray and ultraviolet energies at the same time. Imaging began in 2011 and is expected to complete this summer.

"The Swift survey leverages infrared imaging previously compiled by NASA's Spitzer Space Telescope and extends it into higher energies," said team member Michael Siegel, a research associate at the Swift Mission Operations Center (MOC) in State College, Pa., which is operated by Penn State University.

"The infrared and X-ray surveys complement each other because light at these energies penetrates dust clouds in the galactic plane, while the ultraviolet is largely extinguished."

On Feb. 22, 2011, Swift imaged a survey field near the southern border of the constellation Centaurus.

Although nothing unusual appeared in the ultraviolet exposure, the X-ray image revealed an extended, semi-circular source reminiscent of a supernova remnant.

A search of archival data revealed counterparts in Spitzer infrared imagery and in radio data from the Molonglo Observatory Synthesis Telescope in Australia.

To further investigate the object, the team followed up with an 83-minute exposure using NASA's Chandra X-ray Observatory and additional radio observations from the Australia Telescope Compact Array (ATCA), located near the town of Narrabri in New South Wales.

"The fantastic sensitivity of ATCA has enabled us to image what, at radio wavelengths, turns out to be the dimmest remnant we have ever seen in our galaxy," said team member Cleo Loi, an undergraduate student at the University of Sydney who led the analysis of the radio observations.

A paper describing the team's findings will appear in an upcoming edition of The Astrophysical Journal and was published online on Friday.

Using an estimated distance of 26,000 light-years for G306.3-0.9, the scientists determined that the explosion's shock wave is racing through space at about 1.5 million mph (2.4 million km/h).

The Chandra observations reveal the presence of iron, neon, silicon and sulfur at temperatures exceeding 50 million degrees F (28 million C), a reminder not only of the energies involved but of the role supernovae play in seeding the galaxy with heavy elements produced in the hearts of massive stars.

"We don't yet have enough information to determine what type of supernova this was and therefore what type of star exploded, but we've planned a further Chandra observation to improve the picture," said coauthor Jamie Kennea, also a researcher at the Swift MOC.

"We see no compelling evidence that the explosion formed a neutron star, and this is something we hope can be determined one way or the other by future work."

Supernova Explosion: Galaxy's Youngest Black Hole

W49B is much more barrel-shaped than most other remnants in X-rays and several other wavelengths, pointing to an unusual demise for this star.

The highly distorted supernova remnant shown in this image may contain the most recent black hole formed in the Milky Way galaxy. 

The image combines X-rays from NASA's Chandra X-ray Observatory in blue and green, radio data from the NSF's Very Large Array in pink, and infrared data from Caltech's Palomar Observatory in yellow.

The remnant, called W49B, is about a thousand years old, as seen from Earth, and is at a distance of about 26,000 light years away.

The supernova explosions that destroy massive stars are generally symmetrical, with the stellar material blasting away more or less evenly in all directions.

However, in the W49B supernova, material near the poles of the doomed rotating star was ejected at a much higher speed than material emanating from its equator. Jets shooting away from the star's poles mainly shaped the supernova explosion and its aftermath.

By tracing the distribution and amounts of different elements in the stellar debris field, researchers were able to compare the Chandra data to theoretical models of how a star explodes.

For example, they found iron in only half of the remnant while other elements such as sulfur and silicon were spread throughout. This matches predictions for an asymmetric explosion.

Also, W49B is much more barrel-shaped than most other remnants in X-rays and several other wavelengths, pointing to an unusual demise for this star.

The authors also examined what sort of compact object the supernova explosion left behind. Most of the time, massive stars that collapse into supernovas leave a dense spinning core called a neutron star.

VST Image: Star-forming Region Messier 17 - Omega Nebula

The first released VST image shows the spectacular star-forming region Messier 17, also known as the Omega Nebula or the Swan Nebula, as it has never been seen before. 

This vast region of gas, dust and hot young stars lies in the heart of the Milky Way in the constellation of Sagittarius (The Archer). 

The VST field of view is so large that the entire nebula, including its fainter outer parts, is captured — and retains its superb sharpness across the entire image. 

The data was processed using the Astro-WISE software system developed by E.A. Valentijn and collaborators at Groningen and elsewhere.

Credit: ESO/INAF-VST/OmegaCAM. Acknowledgement: OmegaCen/Astro-WISE/Kapteyn Institute

When Galaxies Collide: Skater Galaxies

Connected via a long stellar bridge, the two galaxies in UGC 8335 are pulling one another gravitationally with all their might.

The collision is happening 400 million light-years away in the constellation Ursa Major.

Image: NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)