Paper Title: A 200-Second Quasi-Periodicity After the Tidal Disruption of a Star by a Dormant Black Hole
Authors: R. C. Reis, J. M. Miller, M. T. Reynolds, K. Gültekin, D. Maitra, A. L. King, T. E. Strohmayer
First Author’s Institution: University of Michigan Department of Astronomy
Black holes consuming stars has been observed many times in the past (see related Astrobites articles here and here), but this one is special because it is a supermassive black hole, rather than a stellar-mass or intermediate-mass black hole. Here’s the breakdown of what happened that fateful day (Fig. 1): A wandering star passed near the supermassive black hole. As it approached, intense tidal forces distorted the star and began to rip it apart. The stellar material circled in towards the black hole and heated up to millions of degrees. Gas at that temperature emits X-rays, which is what was seen here at Earth. As material began to fall into the black hole, two large jets formed along the black hole’s rotational axis. The formation of these jets are not entirely understood, but it is believed to be a result of twisted magnetic fields that accelerate material away from the black hole at nearly the speed of light.
The in-falling matter causes the X-rays to flicker slightly around certain frequencies. This flickering phenomenon is called a quasi-periodic oscillation (QPO), and serves as a rare glimpse into the regions closest to the event horizon of the black hole. The frequency of this QPO was about 5 mHz. If we could hear sounds at frequencies that low, it would sound like a D-sharp. This star screamed as it was slowly devoured by the black hole. The poor thing never stood a chance.The Silver LiningAlthough the death of a star may be sad (and frightening), the star does not die in vain. Surprisingly, observing the quasi-periodic oscillations of the doomed giant can help us better understand general relativity. The subject of study in this case is the Lense-Thirring effect. The idea is that massive rotating bodies drag space itself around them. If an object is revolving around that massive rotating body, its plane of revolution will precess. The problem is that we don’t have many super massive and rapidly rotating objects laying around that we can use to test this idea. Thanks to QPO’s, physicists have the laboratory they need to study this phenomenon. The authors haven’t conducted any relativity studies with this information yet, but the resources are there and somebody is likely to use it before too long.