About 290 million years ago, a Sun-like star got too close to its galaxy’s central black hole. Consequently, the close proximity led to powerful tides that tore apart the star, producing a burst of optical, ultraviolet and X-ray light. The event, named ASASSN-14li, could be first viewed from Earth in 2014. Now, a team of scientists have mapped out how and where the different wavelengths were created as the debris of the destroyed star circled the black hole.
"We discovered brightness changes in X-rays that occurred about a month after similar changes were observed in visible and UV light," Massachusetts Institute of Technology (MIT) astrophysicist Dheeraj Pasham said. "We think this means the UVl and optical emission arose far from the black hole, where elliptical streams of orbiting matter collided into each other."
When a star gets too near a black hole that measures 10,000 or more times its mass, the star’s own gravity is outstripped by tidal forces. This converts the star into a debris stream, an event termed as tidal disruption. The flares from a tidal disruption event carry important information about how the debris settles into an accretion disk initially. Based on the observations of ASASSN-14li, the scientists inferred that the X-ray emission from its tidal disruption flares arose quite close to the black hole.
Incidentally, ASASSN-14li was first spotted on Nov. 22, 2014 through images captured by the All Sky Automated Survey for SuperNovae (ASASSN), comprising of robotic telescopes in Chile and Hawaii. NASA’s Swift's X-ray and Ultraviolet/Optical telescope were used for follow-up observations.
The research was further augmented with optical data provided by Las Cumbres Observatory in California. The study published in The Astrophysical Journal Letters describes how interactions between the infalling debris could produce the observed UV and optical emission.