December 13, 2016 6:38:37 pm
An intense flare detected last year in a distant galaxy about four billion light years from Earth, considered to be the brightest supernova ever observed, is actually a tidal disruption event (TDE) — the destruction of a star by a rapidly spinning supermassive black hole, suggests new research.
The findings are based on new astronomical observation data from the Las Cumbres Observatory (LCO), a global robotic telescope network, and the Hubble Space Telescope. “We observed the source for 10 months following the event and have concluded that the explanation is unlikely to lie with an extraordinarily bright supernova,” said lead researcher Giorgos Leloudas from Weizmann Institute of Science in Israel.
“Our results indicate that the event was probably caused by a rapidly spinning supermassive black hole as it destroyed a low-mass star,” Leloudas explained.
Using images from the Hubble Space Telescope that were not available when the event, called ASASSN-15lh, was observed, the scientists found that the event occurred at the centre of the galaxy where the supermassive black hole resides. The black hole inferred to lie in this galaxy is more than 100 million times the mass of the sun.
For a star to be tidally disrupted by such a massive black hole — rather than swallowed whole — the black hole must be spinning very rapidly, said the study published in the journal Nature Astronomy. This discovery marks the first time that a TDE has been used to probe the spin of a black hole, a property that is very difficult to measure and is used to infer the existence of so-called Kerr black holes.
ASASSN-15lh occurred when the star strayed too close to the supermassive black hole and was torn apart by the tides generated by the extreme gravity. The stellar material orbited around the black hole, collided with itself at high velocity and started falling into the black hole. This released copious amounts of energy and generated the bright flare astronomers observed as ASASSN-15lh.
“Years ago we just wouldn’t have been able to follow an event like this,” study co-author Andy Howell, University of California, Santa Barbara, US, noted.
“This study shows that large area surveys, a global robotic telescope network and a NASA satellite can come together to reveal dramatic new discoveries that wouldn’t be possible without each piece of that puzzle,” Howell said.
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