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Black hole caught in the act of ripping apart a star

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22 October 2015

Astronomers have observed material being blown away from a black hole after it tore a star apart in the center of a galaxy that is about 290 million light years away from Earth. The event, known as a “tidal disruption,” is depicted in this artist’s illustration. The observations were made with a trio of orbiting observatories that includes NASA’s Swift Gamma-Ray-Burst Explorer. Science and flight operations for Swift are controlled by Penn State from the Mission Operations Center at the University Park campus. This video contains instrumental music only. Credit: NASA's Goddard Space Flight Center/CI Lab

New details about what happens when a black hole tears apart a star have been gathered by a multi-national astronomy team using a trio of orbiting of orbiting observatories that includes NASA’s Swift Gamma-ray-Burst Explorer. Science and flight operations for Swift are controlled by Penn State from the Mission Operations Center at the University Park campus.

The astronomers tracked material being blown away from a black hole after it tore a star apart in the center of a galaxy that is about 290 million light years away from Earth. The new observations give scientists an extraordinary opportunity to understand the extreme environment and events around a black hole.

"Swift is uniquely equipped to make rapid-response observations to fast-breaking events throughout the universe," said John Nousek, Swift’s director of mission operations and a professor of astronomy and astrophysics at Penn State. This event occurred near a supermassive black hole estimated to weigh a few million times the mass of the Sun. The black hole is located in the center of PGC 043234, a galaxy that lies about 290 million light years from Earth. This event is the closest tidal disruption discovered in a decade.

When a star comes too close to a black hole, the intense gravity of the black hole results in tides that can rip the star apart. In these events, called “tidal disruptions,” some of the stellar debris is flung outward at high speeds, while the rest falls toward the black hole, causing distinct X-ray flares that can last for a few years.

To make the observations, they used NASA's Swift observatory, NASA's Chandra X-ray observatory, and the ESA (European Space Agency)/NASA XMM-Newton observatory. Swift carries two telescopes whose lead scientists are Penn State astronomers and a third telescope led by a NASA scientist. In 2014, NASA gave its top ranking to the Swift observatory for all of its astronomy satellites other than two of its “great observatories,” the Hubble Space Telescope and Chandra X-ray Observatory.

NASA’s Chandra X-ray Observatory, Swift Gamma-ray Burst Explorer, and ESA/NASA’s XMM-Newton collected different pieces of this astronomical puzzle in a tidal disruption event called ASASSN-14li, originally discovered in an optical search by the All-Sky Automated Survey for Supernovae (ASAS-SN) in November 2014.

After the star is destroyed, the black hole’s strong gravitational force pulls most of the remains of the star toward it. This infalling debris is heated to millions of degrees and generates a huge amount of X-ray light. Soon after this surge of X-rays, the amount of light decreases as the material falls beyond the black hole's event horizon, the point beyond which no light can escape.

Gas often falls toward black holes by spiraling inward in a disk. But how this process starts has remained a mystery. In ASASSN-14li, astronomers were able to witness the formation of such a disk by looking at the X-ray light at different wavelengths (known as the "X-ray spectrum") and tracking how that changed over time.

Astronomers are hoping to find more events like ASASSN-14li, which they can use to continue to test theoretical models about how black holes affect their environments and anything that might wander too close.

These results are published in the October 22, 2015 issue of the journal Nature. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations. Swift is managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland, and its science and flight operation are controlled by Penn State University from the Mission Operations Center on the University Park campus. XMM-Newton is a joint NASA-European Space Agency orbiting observatory.

[ Barbara K. Kennedy ]

CONTACTS

John Nousek: nousek@swift.psu.edu, 814-863-1937

Barbara Kennedy (PIO):  science@psu.edu, 814-863-4682

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