Black holes eat stars. We know this. We’ve managed to catch it happening. And now we’ve managed to find a star that is regularly flaring up as it swoops by its black hole. It is so regular, in fact, that it’s being called “Old Faithful” as it flashes every 114 days like clockwork.
In new work presented at the AAS meeting and soon to be published in The Astrophysical Journal, scientists used data from NASA’sSwift Observatory and TESS spacecraft and the telescopes in the All-Sky Automated Survey for Supernovae Network, or ASAS-SN, to observe the star and its regular flashes of light. The object is now called ASASSN-14ko, and it resides in our southern skies in a galaxy about 570 million light-years away.
The first flare was detected back in 2014, and it was thought to be a supernova. Then, lead author Anna Payne went back through the data in 2020 and found seventeen flares, all 114 days apart. This type of regular flare had never been seen before. So the team predicted that the galaxy would flare on May 17, 2020, joint observations were coordinated, and voila! The flare happened right on schedule. It was followed by two more predicted and observed flares in September and December of last year.
Basically, there is a star orbiting its galaxy that passes close enough to its black hole every 114 days to cause a flare as matter is pulled from it in a burst of energy. The black hole is estimated to be 20 times the mass of our own Milky Way’s SagA*. And one of the co-leads of the ASAS-SN project says there is even evidence of a second supermassive black hole in that galaxy.
Co-author Kris Stanek summed the work: In general, we really want to understand the properties of these black holes and how they grow. It gives us a truly unique opportunity to better understand the phenomenon of episodic mass accretion on supermassive black holes. The ability to exactly predict the timing of the next episode allows us to take data that we could not otherwise take, and we are taking such data already.
I’m sure we’ll hear more about this work in the coming months.
“ASASSN-14ko is a Periodic Nuclear Transient in ESO 253-G003,” Anna V. Payne et al., to be published in The Astrophysical Journal (preprint on arxiv.org)