Certain supermassive black holes in post-merger galaxies seem to follow a steady diet of one star per year suggests new observations of the stars orbiting in the extreme proximity of one of these gargantuan objects.
The research, conducted by the University of Colorado Boulder, looked at how the asymmetrical stellar cluster surrounding them form, how their orbits remain stable, and how long they last. The longevity has implication on the black feeding periods.
As reported in the Astrophysical Journal, black holes are usually surrounded by nice and regular symmetric star clusters. But in several galaxies, including nearby Andromeda, these nuclear star clusters are asymmetric. The researchers suspect this as a consequence of a galaxy merger, where a lot of gas is pulled towards the core of the galaxies during the collision of the two black holes, leaving a warped cluster behind.
“The force builds up in these stellar orbits and changes their shape,” lead author Professor Ann-Marie Madigan said in a statement. “Eventually, a star reaches its nearest approach to the black hole and it gets shredded.”
The team showed that the movements of all these stars are influenced by a stabilizing mechanism that keeps the cluster together but once in a while could force a stellar orbit to oscillate in a way that the star ends up beyond the point of no return, getting destroyed by the supermassive black hole.
“We predict that in a post-galactic merger period, a supermassive black hole will swallow one star per year,” said co-author Heather Wernke, a CU Boulder graduate student. “That’s 10,000 times more often than other rate predictions.”
The team focused on the eccentric disk within the core of the Andromeda galaxy, which is just 2 million light-years away. Many scientists suspect the cosmic sibling of the Milky Way to have undergone a galactic collision, billions of years ago.
“Andromeda is likely past the peak of this process, having undergone a merger long ago,” said Madigan, who is also an assistant professor in CU Boulder’s Department of Astrophysical and Planetary Sciences. “But with higher resolution data, we may be able to find younger eccentric disks in more distant galactic nuclei.”