"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.
To make the observations, the researchers used NASA's Swift observatory, NASA's Chandra X-ray observatory, and the ESA (European Space Agency)/NASA XMM-Newton observatory to collect 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. Their results were published in the October 22, 2015 issue of the journal Nature.
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 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 in distinct flares that can last for a few years. 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.
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 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.