NASA mission to go on with private funding

For nine years the Galaxy Evolution Explorer surveyed the sky with ultraviolet eyes in a NASA mission to catalog hundreds of millions of galaxies spanning 10 billion years of cosmic time.

The spacecraft was placed in standby mode Feb. 7 while NASA and Caltech worked out a Space Act Agreement, signed May 14, to allow the university to resume spacecraft operations and data management for the mission, the agency reported.

"NASA sees this as an opportunity to allow the public to continue reaping the benefits from this space asset that NASA developed using federal funding," said Paul Hertz, director of the agency's astrophysics division at NASA headquarters in Washington.

"This is an excellent example of a public/private partnership that will help further astronomy in the United States."Under the agreement, NASA maintains ownership and liability for the spacecraft until Caltech completes science activities, at which time it will decommission the spacecraft for NASA.The mission's batteries and solar panels have an expected lifetime of 12 years or more, NASA said.

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NASA's Chandra Sees Remarkable Outburst From Old Black Hole

An extraordinary outburst produced by a black hole in a nearby galaxy has provided direct evidence for a population of old, volatile stellar black holes. The discovery, made by astronomers using NASA's Chandra X-ray Observatory, provides new insight into the nature of a mysterious class of black holes that can produce as much energy in X-rays as a million suns radiate at all wavelengths.

Researchers used Chandra to discover a new ultraluminous X-ray source, or ULX. These objects give off more X-rays than most binary systems, in which a companion star orbits the remains of a collapsed star. These collapsed stars form either a dense core called a neutron star or a black hole.

The extra X-ray emission suggests ULXs contain black holes that might be much more massive than the ones found elsewhere in our galaxy.

The companion stars to ULXs, when identified, are usually young, massive stars, implying their black holes are also young. The latest research, however, provides direct evidence that ULXs can contain much older black holes and some sources may have been misidentified as young ones.

The intriguing new ULX is located in M83, a spiral galaxy about 15 million light years from Earth, discovered in 2010 with Chandra. Astronomers compared this data with Chandra images from 2000 and 2001, which showed the source had increased in X-ray brightness by at least 3,000 times and has since become the brightest X-ray source in M83.

The sudden brightening of the M83 ULX is one of the largest changes in X-rays ever seen for this type of object, which do not usually show dormant periods. No sign of the ULX was found in historical X-ray images made with Einstein Observatory in 1980, ROSAT in 1994, the European Space Agency's XMM-Newton in 2003 and 2008, or NASA's Swift observatory in 2005.

"The flaring up of this ULX took us by surprise and was a sure sign we had discovered something new about the way black holes grow," said Roberto Soria of Curtin University in Australia, who led the new study. The dramatic jump in X-ray brightness, according to the researchers, likely occurred because of a sudden increase in the amount of material falling into the black hole.

In 2011, Soria and his colleagues used optical images from the Gemini Observatory and NASA's Hubble Space Telescope to discover a bright blue source at the position of the X-ray source. The object had not been previously observed in a Magellan Telescope image taken in April 2009 or a Hubble image obtained in August 2009.

The lack of a blue source in the earlier images indicates the black hole's companion star is fainter, redder and has a much lower mass than most of the companions that previously have been directly linked to ULXs. The bright, blue optical emission seen in 2011 must have been caused by a dramatic accumulation of more material from the companion star.

"If the ULX only had been observed during its peak of X-ray emission in 2010, the system easily could have been mistaken for a black hole with a massive, much younger stellar companion, about 10 to 20 million years old," said co-author William Blair of Johns Hopkins University in Baltimore.

The companion to the black hole in M83 is likely a red giant star at least 500 million years old, with a mass less than four times the sun's. Theoretical models for the evolution of stars suggest the black hole should be almost as old as its companion.

Another ULX containing a volatile, old black hole recently was discovered in the Andromeda galaxy by Amanpreet Kaur, from Clemson University, and colleagues and published in the February 2012 issue of Astronomy and Astrophysics.

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NASA’s Chandra Finds Largest Galaxy Cluster in Early Universe

An exceptional galaxy cluster, the largest seen in the distant universe, has been found using NASA’s Chandra X-ray Observatory and the National Science Foundation-funded Atacama Cosmology Telescope (ACT) in Chile.

Officially known as ACT-CL J0102-4915, the galaxy cluster has been nicknamed “El Gordo” (“the big one” or “the fat one” in Spanish) by the researchers who discovered it. The name, in a nod to the Chilean connection, describes just one of the remarkable qualities of the cluster, which is located more than 7 billion light years from Earth. This large distance means it is being observed at a young age.

“This cluster is the most massive, the hottest, and gives off the most X-rays of any known cluster at this distance or beyond,” said Felipe Menanteau of Rutgers University in New Brunswick, N.J., who led the study.

Galaxy clusters, the largest objects in the universe that are held together by gravity, form through the merger of smaller groups or sub-clusters of galaxies. Because the formation process depends on the amount of dark matter and dark energy in the universe, clusters can be used to study these mysterious phenomena.

Dark matter is material that can be inferred to exist through its gravitational effects, but does not emit and absorb detectable amounts of light. Dark energy is a hypothetical form of energy that permeates all space and exerts a negative pressure that causes the universe to expand at an ever-increasing rate.

“Gigantic galaxy clusters like this are just what we were aiming to find,” said team member Jack Hughes, also of Rutgers. “We want to see if we can understand how these extreme objects form using the best models of cosmology that are currently available.”

Although a cluster of El Gordo’s size and distance is extremely rare, it is likely that its formation can be understood in terms of the standard Big Bang model of cosmology. In this model, the universe is composed predominantly of dark matter and dark energy, and began with a Big Bang about 13.7 billion years ago.

The team of scientists found El Gordo using ACT thanks to the Sunyaev-Zeldovich effect. In this phenomenon, photons in the cosmic microwave background interact with electrons in the hot gas that pervades these enormous galaxy clusters. The photons acquire energy from this interaction, which distorts the signal from the microwave background in the direction of the clusters. The magnitude of this distortion depends on the density and temperature of the hot electrons and the physical size of the cluster.

X-ray data from Chandra and the European Southern Observatory’s Very Large Telescope, an 8-meter optical observatory in Chile, show El Gordo is, in fact, the site of two galaxy clusters colliding at several million miles per hour. This and other characteristics make El Gordo akin to the well-known object called the Bullet Cluster, which is located almost 4 billion light years closer to Earth.

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NASA's Hubble Confirms That Galaxies Are the Ultimate Recyclers

New observations by NASA's Hubble Space Telescope are expanding astronomers' understanding of the ways in which galaxies continuously recycle immense volumes of hydrogen gas and heavy elements. This process allows galaxies to build successive generations of stars stretching over billions of years.

This ongoing recycling keeps some galaxies from emptying their "fuel tanks" and stretches their star-forming epoch to over 10 billion years.

This conclusion is based on a series of Hubble Space Telescope observations that flexed the special capabilities of its Cosmic Origins Spectrograph (COS) to detect gas in the halo of our Milky Way and more than 40 other galaxies. Data from large ground-based telescopes in Hawaii, Arizona and Chile also contributed to the studies by measuring the properties of the galaxies.

Astronomers believe that the color and shape of a galaxy is largely controlled by gas flowing through an extended halo around it. The three studies investigated different aspects of the gas-recycling phenomenon.

The results are being published in three papers in the November 18 issue of Science magazine. The leaders of the three studies are Nicolas Lehner of the University of Notre Dame in South Bend, Ind.; Jason Tumlinson of the Space Telescope Science Institute in Baltimore, Md.; and Todd Tripp of the University of Massachusetts at Amherst.

The COS observations of distant stars demonstrate that a large mass of clouds is falling through the giant halo of our Milky Way, fueling its ongoing star formation. These clouds of hot hydrogen reside within 20,000 light-years of the Milky Way disk and contain enough material to make 100 million suns. Some of this gas is recycled material that is continually being replenished by star formation and the explosive energy of novae and supernovae, which kicks chemically enriched gas back into the halo.

The COS observations also show halos of hot gas surrounding vigorous star-forming galaxies. These halos, rich in heavy elements, extend as much as 450,000 light-years beyond the visible portions of their galactic disks. The amount of heavy-element mass discovered far outside a galaxy came as a surprise. COS measured 10 million solar masses of oxygen in a galaxy's halo, which corresponds to about one billion solar masses of gas -- as much as in the entire space between stars in a galaxy’s disk.

Researchers also found that this gas is nearly absent from galaxies that have stopped forming stars. In these galaxies, the “recycling” process ignites a rapid firestorm of star birth which can blow away the remaining fuel, essentially turning off further star-birth activity.

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NASA's Hubble Observes Young Dwarf Galaxies Bursting With Stars

Using its near-infrared vision to peer 9 billion years back in time, NASA's Hubble Space Telescope has uncovered an extraordinary population of young dwarf galaxies brimming with star formation. While dwarf galaxies are the most common type of galaxy in the universe, the rapid star-birth observed in these newly found examples may force astronomers to reassess their understanding of the ways in which galaxies form.

The galaxies are a hundred times less massive, on average, than the Milky Way, yet churn out stars at such a furious pace that their stellar content would double in just 10 million years. By comparison, the Milky Way would take a thousand times longer to double its star population.

The universe is estimated to be 13.7 billion years old, and these newly discovered galaxies are extreme even for the young universe -- when most galaxies were forming stars at higher rates than they are today. Astronomers using Hubble's instruments could spot the galaxies because the radiation from young, hot stars has caused the oxygen in the gas surrounding them to light up like a bright neon sign.

"The galaxies have been there all along, but up until recently astronomers have been able only to survey tiny patches of sky at the sensitivities necessary to detect them," said Arjen van der Wel of the Max Planck Institute for Astronomy in Heidelberg, Germany, lead author of a paper on the results being published online on Nov. 14 in The Astrophysical Journal. "We weren't looking specifically for these galaxies, but they stood out because of their unusual colors."

The observations were part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), an ambitious three-year study to analyze the most distant galaxies in the universe. CANDELS is the first census of dwarf galaxies at such an early epoch.

"In addition to the images, Hubble has captured spectra that show us the oxygen in a handful of galaxies and confirmed their extreme star-forming nature," said co-author Amber Straughn at NASA's Goddard Space Flight Center in Greenbelt, Md. "Spectra are like fingerprints. They tell us the galaxies' chemical composition."

The resulting observations are somewhat at odds with recent detailed studies of the dwarf galaxies that are orbiting as satellites of the Milky Way.

"Those studies suggest that star formation was a relatively slow process, stretching out over billions of years," explained Harry Ferguson of the Space Telescope Science Institute (STScI) in Baltimore, Md., co-leader of the CANDELS survey. "The CANDELS finding that there were galaxies of roughly the same size forming stars at very rapid rates at early times is forcing us to re-examine what we thought we knew about dwarf galaxy evolution."

The CANDELS team uncovered the 69 young dwarf galaxies in near-infrared images taken with Hubble's Wide Field Camera 3 and Advanced Camera for Surveys.

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