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Star shredded by supermassive black hole

posted Nov 9, 2015, 7:24 AM by Jeremy Drake
Strong gravity close to massive black holes can tear stars apart if they get too close.  The disruption occurs because of tidal forces - the side of the star closest to the black hole is attracted more strongly than that further away.  The shredded star material circles in around the black hole in a disk, heating up in the process and radiating with terrific intensity from optical to X-ray wavelengths. 

On November 22, 2014 the All-Sky Automated Survey for Supernovae (ASAS-SN) discovered a bright object, dubbed ASASSN-14li, that appeared to be coincident with the center of the galaxy PGC 043234 lying 290 million light years away. The way the light intensity from the event evolved matched that expected from a stellar "tidal disruption event". A group of us lead by astrophysicist Jon Miller at the University of Michigan used three X-ray telescopes - NASA's Chandra X-ray Observatory, Swift Gamma Ray Burst Explorer, and ESA's XMM-Newton - to observe the high energy emission expected from the nascent disk of shredded star material. 

The Chandra and XMM-Newton spectra showed evidence of material moving outward from the object at speeds of a few hundred km per second - too slow to escape the gravitational field of the black hole. This material is probably levitated by the pressure of the intense light from the energised gas, similar to the radiatively-driven outflows of massive stars discussed in a recent posting. The gas flow is consistent with a rotating wind from the inner region of the disk, or with a filament of disrupted stellar gas at the further reaches of its elliptical orbit.  The results will help constrain theories of tidal disruption and accretion disk formation.  This study was published in the October 22nd issue of Nature and also featured in a press release.
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