COLUMBUS, Ohio — The astronomical version of “Old Faithful” occurs every 114 days, according to scientists from The Ohio State University. The phenomenon is a stellar flare that occurs when a black hole tears parts of a star away from its body. This causes large flashes of light that occur in a predictable pattern.
Using telescopes and data from NASA, the discovery is the first indication of stellar flares erupting in a predictable pattern from the center of the galaxy. “It’s really exciting because we’ve seen black holes do a lot of things, but we’ve never seen them do something like this – cause this regular eruption of light – before. It’s like an extra-galactic Old Faithful,” says Patrick Vallely, a co-author of the study and National Science Foundation Graduate Research Fellow at OSU, in a statement.
The flare stems from the galaxy’s core, about 570 million light-years away. In earlier observations, researchers saw the star being destroyed by tidal disturbances. However, scientists believe the star is actually moving around a black hole which is ripping parts of the star away each time causing the flare.
The flashes of light are referred to as ASASSN-14ko, short for All-Sky Automated Survey for Supernovae (ASAS-SN). This is a group of 20 different telescopes used to collect data at Ohio State. “Knowing the schedule of this extragalactic Old Faithful allows us to coordinate and study it in more detail,” explains Anna Payne, lead author of the paper and a NASA Fellow at the University of Hawai’i at Mānoa.
When the flare was first observed by the ASAS-SN, astronomers thought it was a supernova. However, as the observance revealed the repeatable pattern, they examined the phenomenon more closely. Payne discovered 17 different flare events taking place 114 days apart, which has never before been observed.
Given the predictable nature, the team was able to join together with both space- and ground-based facilities to observe the flares that occurred in May, September, and December of 2020. Payne and the team studied a past flare using TESS data to obtain details including the hike, peak, and the reduction.
“TESS provided a very thorough picture of that particular flare, but because of the way the mission images the sky, it can’t observe all of them. ASAS-SN collects less detail on individual outbursts but provides a longer baseline, which was crucial in this case. The two surveys complement one another,” explains Vallely.
The black hole causing the flares is approximately 20 times the size of the Milky Way’s black hole. “There is evidence that a second supermassive black hole exists in that galaxy. The galaxy that hosts this object is something of a ‘trainwreck’ consisting of two galaxies in the process of merging into one,” says Chris Kochanek, an astronomy professor at OSU, and co-lead of the ASAS-SN project.
The astronomers say that although we have only recently observed the flares, they have occurred 600 million years ago. This is because the galaxy is a great distance away and the light has taken that amount of time to be observed by us. “There was life on Earth, but it was all very primitive,” adds Kris Stanek, a co-author on the paper and university distinguished professor of astronomy at OSU.
“In general, we really want to understand the properties of these black holes and how they grow. Because the eruptions from this black hole happen regularly and predictably, 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,” says Stanek.
The study is published in The Astrophysical Journal.