Monster Black Hole Caught Feeding in Galaxy Crash
NASA's black-hole-hunting space telescope NuSTAR has identified a monster black hole gobbling up a pair of colliding galaxies called Arp 299. NuSTAR's view of the galaxy crash is at left, with the Hubble Space Telescope's view on the right. Data from both space telescopes are combined in the central panel.
Credit: NASA/JPL-Caltech/GSFC

A NASA space telescope has spotted a colossal black hole chowing down on gas from a distant collision between two doomed galaxies. Views of the cosmic smashup, which the swirl of gas and dust previously hid, will likely shed light on the evolution of galaxies, scientists say.

The new view of the colliding galaxies — known collectively as Arp 299 — was captured by NASA's Nuclear Spectroscopic Telescope Array (NuSTAR), an X-ray space telescope built to hunt black holes. The galaxies in Arp 299 are about 130 million light-years from Earth and made a close pass by each other about 700 million years ago, sparking a fierce burst of star formation. Now, some stars from the galaxies are turning to dust via huge supernova explosions.

But star formation isn't the only result of such supermassive collisions. As two galaxies merge, the chaos should send gas flowing to the central black holes. This collision-induced feeding frenzy by black holes helps explain how the objects grow to be millions to billions of times the mass of the sun. [NuSTAR: NASA's Black Hole Telescope in Pictures]

"We want to understand the mechanisms that trigger the black holes to turn on and start consuming the gas," the study's lead researcher, Andrew Ptak, of NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in a statement.

Although previous space telescopes, including NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton, have observed Arp 299, they were only able to probe the low-energy X-rays emitted by the collision and unable to see if one or both of the black holes were actively chomping down gas.

"Odds are low that both black holes are on at the same time in a merging pair of galaxies," said co-author Ann Hornschemeier, also of NASA’s Goddard Space Flight Center, referring to the black holes’ ability to munch down gas and shine brightly. "When the cores of the galaxies get closer, however, tidal forces slosh the gas and stars around vigorously, and, at that point, both black holes may turn on."

NASA's NuSTAR space telescope, launched in 2012, is the first observatory capable of spotting high-energy X-rays and therefore making sense of the tangled galaxies in Arp 299. The new image shows that the black hole in the galaxy on the right is indeed the hungry one. Meanwhile, the black hole on the left is likely dormant or hidden by thicker layers of gas and dust.

"Before now, we couldn't pinpoint the real monster in the merger," said Ptak.

Black holes are so bizarre, they sound unreal. Yet astronomers have found good evidence they exist. Test your knowledge of these wacky wonders.
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Black holes are so bizarre, they sound unreal. Yet astronomers have found good evidence they exist. Test your knowledge of these wacky wonders.
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As it approaches the supermassive black hole, the gas grows increasingly hot — so hot that electrons get stripped off of atoms — and a plasma is created. This plasma then boosts the visible light up to high-energy X-rays, detectable by NuSTAR. 

As an added bonus, the galaxies' two black holes themselves will eventually merge, shaking the fabric of space-time and producing gravitational waves that propagate outward like ripples on a pond.

The study, which has been accepted for publication in the Astrophysical Journal, was presented Thursday (Jan. 8) in Seattle at the 225th American Astronomical Society meeting.

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