NASA's Fermi Telescope Detects Gamma Rays From 'Star Factories' In Other Galaxies

Nearby galaxies undergoing a furious pace of star formation also emit lots of gamma rays, say astronomers using NASA's Fermi Gamma-ray Space Telescope. Two so-called "starburst" galaxies, plus a satellite of our own Milky Way galaxy, represent a new category of gamma-ray-emitting objects detected both by Fermi and ground-based observatories.

"Starburst galaxies have not been accessible in gamma rays before," said Fermi team member Seth Digel, a physicist at SLAC National Accelerator Laboratory in Menlo Park, Calif. "Most of the galaxies Fermi sees are exotic and distant blazars, which produce jets powered by matter falling into enormous black holes. But these new galaxies are much closer to us and much more like our own."

Gamma rays are the most energetic form of light. Fermi has detected more than a thousand point sources and hundreds of gamma-ray bursts, but the satellite also detects a broad glow that roughly follows the plane of our galaxy. This diffuse gamma-ray emission results when fast-moving particles called cosmic rays strike galactic gas or even starlight.

Cosmic rays are hyperfast electrons, positrons, and atomic nuclei moving at nearly the speed of light. But, although Earth is constantly bombarded by these particles, their origin remains a mystery nearly a century after their discovery. Astronomers suspect that the rapidly expanding shells of exploded stars somehow accelerate cosmic ray particles to their fantastic energy.

"For the first time, we're seeing diffuse emission from star-forming regions in galaxies other than our own," noted Jürgen Knödlseder, a Fermi collaborator at the Center for the Study of Space Radiation in Toulouse, France. He spoke to reporters today at the 2009 Fermi Symposium, a Washington gathering of hundreds of astrophysicists involved in the Fermi mission and related studies. The meeting continues through Nov. 5.

Knödlseder revealed an image captured by Fermi's Large Area Telescope (LAT) of a star-forming region known as 30 Doradus within the Large Magellanic Cloud (LMC). Located 170,000 light-years away in the southern constellation Dorado, the LMC is the largest of several small satellite galaxies that orbit our own.

More stars form in the 30 Doradus "star factory" than in any similar location in the Milky Way. "The region is an intense source of gamma rays, and the diffuse emission we see with Fermi follows the glowing gas we see in visible light," Knödlseder explained.

The region lights up in gamma rays for the same reason the Milky Way does -- because cosmic rays strike gas clouds and starlight. But Fermi shows that the LMC's brightest diffuse emission remains close to 30 Doradus and doesn't extend across the galaxy. This implies that the stellar factory itself is the source of the cosmic rays producing the glow.

"Star-forming regions produce lots of massive, short-lived stars, which explode when they die," Digel said. "The connection makes sense."

"The tangled magnetic fields near 30 Doradus probably confine the cosmic rays to their acceleration sites," Knödlseder said.

Fermi's LAT sees diffuse emission from the starburst galaxies M82 and NGC 253, both of which were also seen this year by ground-based observatories sensitive to gamma rays hundreds of times more energetic than the LAT can detect. They do this by imaging faint flashes in the upper atmosphere caused by the absorption of gamma rays carrying trillions of times the energy of visible light.

"The core of M82 forms stars at a rate ten times greater than the entire Milky Way galaxy," said Niklas Karlsson, a postdoctoral fellow at Adler Planetarium in Chicago. He is also a member of the science team for VERITAS, an array of gamma-ray telescopes in Arizona that detected M82, which lies 12 million light-years away in the constellation Ursa Major.

"These very-high-energy gamma rays probe physical processes in other galaxies that will help us understand how and where cosmic rays become accelerated," Karlsson explained.

"Our sensitivity to gamma-rays -- both in space and on the ground -- has increased enormously thanks to Fermi and observatories like VERITAS," Digel said. "This is opening up the detailed study of high-energy processes in galaxies very close to home." NASA's Fermi Gamma Ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy, along with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

Galaxy Cluster Smashes Distance Record

The most distant galaxy cluster yet has been discovered by combining data from NASA's Chandra X-ray Observatory and optical and infrared telescopes. The cluster is located about 10.2 billion light years away, and is observed as it was when the Universe was only about a quarter of its present age.

The galaxy cluster, known as JKCS041, 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 found at the cusp 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."

Distant galaxy clusters are often detected first with optical and infrared observations that reveal their component galaxies dominated by old, red stars. 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?

The paper describing the results on JKCS041 from Andreon and his colleagues will appear in an upcoming issue of the journal Astronomy and Astrophysics. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington, DC. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass

Bizarre Galaxy Is Result Of Pair Of Spiral Galaxies Smashing Together

A recent NASA/ESA Hubble Space Telescope image captures what appears to be one very bright and bizarre galaxy, but is actually the result of a pair of spiral galaxies that resemble our own Milky Way smashing together at breakneck speeds. The product of this dramatic collision, called NGC 2623, or Arp 243, is about 250 million light-years away in the constellation of Cancer (the Crab).

Not surprisingly, interacting galaxies have a dramatic effect on each other. Studies have revealed that as galaxies approach one another massive amounts of gas are pulled from each galaxy towards the centre of the other, until ultimately, the two merge into one massive galaxy. The object in the image, NGC 2623, is in the late stages of the merging process with the centres of the original galaxy pair now merged into one nucleus. However, stretching out from the centre are two tidal tails of young stars showing that a merger has taken place. During such a collision, the dramatic exchange of mass and gases initiates star formation, seen here in both the tails.

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 have 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 harbour very young stars in the early stages of their evolutionary journey.

Some mergers (including NGC 2623) can result in an active galactic nucleus, where one of the supermassive black holes found at the centres 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 some of the most advanced space-based telescopes, including Hubble. Additional data from infrared and X-ray telescopes can further characterise objects like active galactic nuclei and nuclear star formation by revealing what is unseen at visible wavelengths.

The GOALS project includes data from NASA/ESA's Hubble Space Telescope, NASA's Spitzer Space Telescope, NASA's Chandra X-ray Observatory and NASA's Galaxy Evolution Explorer (GALEX). The joint efforts of these powerful observing facilities have provided a clearer picture of our local Universe.

This data used for this colour composite were taken in 2007 by the Advanced Camera for Surveys (ACS) aboard Hubble. The observations were led by astronomer Aaron S. Evans. A team of over 30 astronomers, including Evans, recently published an important 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.

Let There Be Blobs: Mystery Object Spotted in the Early Universe

Looking deep into the sky—and, by extension, far back in time—astronomers have spotted a curious space blob that existed when the universe was only 800 million years old, about 6 percent of its present age.

Masami Ouchi, a fellow at The Observatories of the Carnegie Institution in Pasadena, Calif., who led the research reported in the May 10 issue of the Astrophysical Journal, says that the luminous gas cloud, which spans some 55,000 light-years (about half the diameter of the Milky Way), is unique for its time. "There are no extended objects found at such an early epoch," he says. Other known objects in its class, called Lyman-alpha blobs, are from somewhat more recent history, Ouchi says—at least two billion to three billion years after the big bang.

Lyman-alpha blobs are an astronomical mystery that may be primordial galaxies. "The consensus is that these are enormous protogalaxies, which over the course of time will yield very massive old galaxies such as we see in the local universe," says Dan Smith, a postdoctoral researcher at Liverpool John Moores University in England. Smith, who was not involved in the study, calls the detection of such an early Lyman-alpha blob "a very exciting result."

But as of now, it is not known what Lyman-alpha blobs are or what causes them to glow. Resolving the proposed explanations for these early objects could shed light on how galaxies such as the Milky Way take shape. Some theories hold that Lyman-alpha blobs are formed by inflows of cold streams of gas, a mechanism that Smith points out has recently been suggested by some researchers as the dominant mode of galaxy growth. Other explanations posit that the blobs' gas emits radiation due to heating by an active galactic nucleus harboring a churning object such as a supermassive black hole or by an accelerated phase of star formation known as a starburst.

The Lyman-alpha blob has been dubbed Himiko, after a queen in ancient Japan. "I found the name of Himiko is very suitable," Ouchi says, "given the fact that this object was discovered in an ancient universe [by] the Subaru Telescope," which is operated by the National Astronomical Observatory of Japan.

Seeking Out the Sun's Long-Lost Siblings

For decades astronomers have been on the hunt for so-called "solar twins"—stars with the same ages, masses, temperatures, luminosities and chemical abundances as our own sun.

But seeking out solar twins in this way is akin to looking for people on the street wearing a coat like yours and calling them family, says Simon Portegies Zwart, a computational astrophysicist at the University of Amsterdam in the Netherlands.

Instead, Portegies Zwart wants to search for our star's true siblings—those that actually formed alongside our own star and still have the stellar bloodlines to prove it.

Until now, mainstream astronomers have dismissed the idea of actually finding any of our wayward kin, some 4.3 billion years after our stellar birth cluster is believed to have dissipated. But Portegies Zwart, in a new paper (being reviewed for publication in Astrophysical Journal Letters), offers up what may be a credible way to find 50 or 60 of our own sun's original siblings, that small fraction of the estimated 1,000 to 6,000 original cluster members Portegies Zwart thinks is located within some 300 light-years of Earth.

Portegies Zwart proposes identifying stellar relatives via their proper motion, or apparent movement across our line of sight, their position in the sky, and their chemical signatures, which he likens to their stellar DNA. Such stars, he says, would be roughly one solar mass (the size of the sun) or less and have chemical abundances similar to the sun.

"Several months ago," the astrophysicist says, "I would have said looking for the sun's siblings would be absolutely useless."

But Portegies Zwart changed his mind after calculating the sun's velocity backward over the past 4.6 billion years. From that putative starting point in the Centaurus constellation, he then projected how stellar members of our birth cluster would actually disperse forward in time.

"To my surprise," he says, "these stars all sort of stayed in the neighborhood with their proper motions and positions pretty much intact. Whether we can really recognize these stars is still not completely clear. Out of about a million stars within some 300 light-years, the expectation is that about 50 of them are siblings."

Leslie Looney, an astrophysicist at the University of Illinois at Urbana–Champaign, praises the idea in principle but says that astronomers will never know for sure if any given star is a sibling. He believes researchers will, however, be able to narrow down a group of stars that are "likely" kin.

And if observational astronomers were able to identify a few dozen of the sun's relatives, Portegies Zwart says, it would bring a sea change in our understanding of how the solar system formed and evolved.

One of his graduate students is already combing stellar catalogues to find candidates on which to try out the methodology. Portegies Zwart says the best place to look is in the plane of the galaxy, in the constellations of Vela and Cygnus, along the sun's trajectory around the galactic center.

The European Space Agency's 2011 Gaia mission, due to measure the position and motions of a billion stars in our part of the galaxy, should give the effort a boost.

But Eric Mamajek, a University of Rochester astronomer who specializes in stellar dynamics, likens Portegies Zwart's proposal to searching for members of his own 1993 high school class from a random sampling of Manhattan thirtysomethings.

"You might run into a few after an exhaustive search," Mamajek says, "but trying to extrapolate from whence they came based on their current trajectories in life would only lead to frustration."

If galaxies are all moving apart, how can they collide?

"If galaxies are all moving apart at ever increasing speed, how can they collide?"

—J. Gow, Fairfax, Va.

Cosmologist Tamara Davis, a research fellow at the University of Queensland in Australia and  an associate of the Dark Cosmology Center in Denmark, brings together an answer:

The dynamics of the universe are governed by competing forces whose influence varies with scale, so local forces can override universal forces in discrete regions. On scales larger than galaxy clusters, all galaxies are indeed moving apart at an ever increasing rate. The mutual gravitational attraction between two galaxies at that distance is too small to have a significant effect, so the galaxies more or less follow the general flow of the expansion. But it is a different story in a galaxy's local neighborhood. There the gravitational attraction can be very significant and the interactions much more exciting.

Dark energy, believed to be causing the acceleration of the expansion of the universe, provides a constant outward force that does not dilute as the universe expands. Pitted against this relentless push is the gravitational pull from the rest of the matter and energy in the universe. Early on, the universe was much denser than it is today, and the attractive force of gravity was winning the battle, on scales both large and small. Clouds of gas condensed to form stars and galaxies, and galaxies drew together to form clusters. If there had been more matter around, the universe might have started to recollapse before it ever had the chance to accelerate. But matter and energy do dilute as the volume of the universe increases, so dark energy slowly came to dominate. Since about six billion years ago (about a billion years before Earth formed), the expansion has, on average, been accelerating.

Nevertheless, the cosmic dance continues. Galaxies that had been pulled together before the universe began accelerating still have the chance to collide. Collectively they form overdense patches of the universe in which gravity still reigns. In our neighborhood the Andromeda galaxy, our largest companion, is actually falling toward us, and we will have our first close encounter with it in just a few billion years' time.

Our local group comprises Andromeda, the Magellanic Clouds and about 35 other galaxies, all of which lie in an even larger cluster called Virgo. Together we will travel through the expanding universe, and we had better learn to like the company any galaxies that have not yet won the gravity war have missed their chance. The universe is now split into pockets of interaction that will drift alone through the expanding cosmos.

Like revelers on a ship, the galaxies in our group will continue to collide and interact in myriad interesting ways, but we will be forever separated from the revelers on other ships sailing away from us in the vast universe.

Astronomical Survey Reveals Andromeda's Galaxy-Gorging Past

A highly detailed survey of the nearby Andromeda Galaxy, which as a nearby spiral galaxy is something of an observational proxy for our own Milky Way, shows the remnants of smaller galaxies that our neighbor appears to have cannibalized.

The Pan-Andromeda Archaeological Survey is not yet complete but is already producing scientific results such as those in this week's Nature. (Scientific American is part of the Nature Publishing Group.) The study's high-resolution look at Andromeda provides further confirmation of the prevailing theory of galactic growth—that today's giant galaxies fed on smaller companions to reach their present size.

The survey, which relies on observations made at the Canada–France–Hawaii Telescope atop Mauna Kea in Hawaii, is led by astrophysicist Alan McConnachie, a research fellow at the National Research Council Canada's Herzberg Institute of Astrophysics in Victoria, British Columbia.

Astronomers enjoy studying Andromeda in part because of its proximity—at 2.5 million light-years away it is close enough to us that individual stars can be resolved within the galaxy. And Andromeda can be seen in its entirety, unlike the Milky Way, in which we are deeply embedded. "If you're inside a city, and you're trying to figure out what that city looks like, it's much harder," McConnachie says. What is more, he adds, Andromeda appears to be a fairly representative spiral galaxy, based on comparisons with others in the universe at large, so unraveling the history of its formation may help astronomers understand how galactic processes work in general.

The dominant cosmological theory holds that galaxies grow through a process of accretion—by cannibalizing smaller galaxies and incorporating their mass in an ever-growing amalgamation. In agreement with similar observations of the Milky Way, the Andromeda survey has found a sort of archaeological record of this process—the fossilized remains of devoured galaxies.

"We have this idea of how we think galaxies form, and that's to do with the merging together of smaller galaxies," McConnachie says. "And if that's true, then when we look over the vast area around a galaxy, we should actually be able to see remnants of the formation process." Those remnants, which McConnachie calls "the partially digested remains of these dwarf galaxies," take the form of large, diffuse streams of stars, former galactic groupings that have been pulled apart by the larger galaxy's gravitational pull.

The Andromeda survey is turning up several of those remnants, just as predicted by the accretion theory. "When I look at this picture, it really makes me happy," says James Bullock, a cosmologist at the University of California, Irvine, who has worked on what galactic formation residues should look like. "This is exactly the kind of thing that we would expect—these streams of stars, this pretty clear evidence that you've had all these past accretion events."

Bullock notes that this is not the first time such evidence has been found—in fact, some of McConnachie's co-authors published evidence for galactic cannibalism in Andromeda in 2001. But each increasingly detailed look at the galaxy provides more examples and, hence, a more convincing case. "You're never that confident in your theory until you really see it proved by observation," Bullock says. "So it's not humdrum; it's exciting in that sense."

The new survey also indicates that Andromeda's growth continues apace, and on a massive scale to boot. The panoramic portrait reveals a possible past interaction between the galaxy and a smaller neighbor, Triangulum, as evidenced by a newly discovered stellar appendage on Triangulum that extends in Andromeda's direction. That feature, based on the research team's simulations, could be explained by a close encounter between the two galaxies in the past few billion years that ripped a section of stars from Triangulum.

"It actually looks as if it is being destroyed by Andromeda," McConnachie says, which would be a surprise given how much distance separates the galaxies. If this assessment is correct, McConnachie says, then in a few billion years' time—around the same time Andromeda and the Milky Way are expected to come together—Andromeda will finish off Triangulum, creating an even larger supergalaxy.

Strange Shapes Seen In Milky Way's Tiny Neighbor

A stunning new image of one of the Milky Way's nearest galactic neighbors, Barnard's Galaxy, reveals rich star formation and curiously-shaped nebulas.


At the relatively close distance of about 1.6 million light-years, Barnard's Galaxy is a member of the Local Group, an archipelago of galaxies that includes our home, the Milky Way.


The galaxy, also known as NGC 6822, was discovered by the American astronomer Edward Emerson Barnard in 1884.


The new image, taken by one of the telescopes at the European Southern Observatory in La Silla, Chile, shows Barnard's Galaxy beneath a sea of foreground stars in the direction of the constellation of Sagittarius (the Archer).


Barnard's Galaxy is a dwarf galaxy that lacks the spiral arms of its neighbors, the Milky Way, Andromeda and the Triangulum galaxies. It is about a tenth of the Milky Way's size, with about 10 million stars — a far cry from the Milky Way's estimated 400 billion.


Reddish nebulas in the new image reveal regions of active star formation, where young, hot stars heat up nearby gas clouds.


Prominent in the upper left of the image is a striking bubble-shaped nebula. At the nebula's center, 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. When two galaxies collide, their gravitational interaction can warp the shapes of the galaxies.