When a star gets too close to a black hole, it can get torn apart by its gravity and eaten over a relatively short period of time, usually no more than a year.
So this latest discovery is particularly fascinating, as astronomers have found a black hole eating the remains of a star for a decade from 2005 to 2015. A study describing the finding, led by Dacheng Lin from the University of New Hampshire, was published yesterday in Nature.
"We have witnessed a star's spectacular and prolonged demise," said Lin in a statement. "Dozens of tidal disruption events have been detected since the 1990s, but none that remained bright for nearly as long as this one."
To make the discovery, the team used NASA’s Chandra X-ray Observatory and Swift satellite, as well as ESA's XMM-Newton. They observed this tidal disruption event (TDE) in a galaxy about 1.8 billion light-years from Earth, with the source of the X-rays seen by the TDE called XJ1500+0154.
This source was found at the center of the galaxy, suggesting it is a supermassive black hole. The three telescopes observed a rapid brightening of the source in X-rays, about 100 times brighter than before.
The authors came to their conclusion that the black hole was eating a star by noting that the material around the black hole often passed the Eddington limit. This is the maximum luminosity that can be achieved by the force of radiation outwards acting against gravity inwards, which the authors say in their paper is “often observed in accreting stellar-mass black holes.”
If this observation is correct, it would mean that black holes can grow even more rapidly than thought. And it could explain how supermassive black holes were able to get so massive, a billion times the mass of the Sun, when the universe was just a billion years old.
As mentioned, the event took place over 10 years. This means it was either a small star being completely torn apart, or the most massive star ever seen in a TDE. In their paper, the authors note it may have been a star two times as massive as our Sun, and they expect the rate of the black hole eating the star to drop over the next 10 years.
Just recently, the complex relationship between a star's magnetic field and a black hole in the process of devouring it was also studied, further showing there is much for us yet to learn about these events.