About every 114 days, almost like a clock, a galaxy 570 million light-years away lights up like a firework. Since 2014, at least, our observatories have recorded this strange behavior; now, astronomers have put the pieces together to find out why.
In the center of the spiral galaxy, called ESO 253-G003, a supermassive black hole is being orbited by a star that, every 114 days, rotates close enough for some of its materials to be dragged upward, causing a bright glow of light. multiple wavelengths. He then walks away and survives to fall back into his next approach.
Due to the regularity of the flares, astronomers have nicknamed the galaxy “Old Faithful,” as the geyser of Yellowstone National Park.
“These are the most predictable and frequent recurring multi-wave flares we’ve seen from the core of a galaxy, and they give us a unique opportunity to study this extragalactic Old Faithful in detail,” said astronomer Anna Payne of the University, the first author of the study. from Hawaii to Manoa.
“We believe that a supermassive black hole in the center of the galaxy creates explosions as it partially consumes a giant star in orbit.”
The flares were first detected in November 2014, collected by the Automated Sky Survey for Supernovae (ASAS-SN). At the time, astronomers thought that illumination was a supernova that occurred in ESO 253-G003.
But in 2020, when Payne examined ASAS-SN data on ESO 253-G003, he found another flare from the same location. And another. And another.
In all, he identified 17 flares, spanning approximately 114 days. Then she and her team predicted that the galaxy would re-emerge on May 17, September 7, and December 26, 2020, and they were right.
They called the repeated flare ASASSN-14ko, and these accurate predictions meant they could make new, more detailed observations of the May flare with NASA’s powerful TESS telescope. Previous observations of other instruments also provided data across a range of wavelengths.
“TESS provided a very comprehensive picture of this particular flame, but because of the way the mission represents the sky, it can’t observe them all,” said Ohio State University astronomer Patrick Vallely . “ASAS-SN collects less detail about individual explosions, but provides a longer baseline, which was crucial in this case. The two surveys complement each other.”
But a supernova flames only once and then fades away, as such an event destroys the original star; so whatever was causing the light eruptions at optical, ultraviolet, and X-ray wavelengths had to be something else.
A supermassive black hole that emits regular flares as it makes an aperitif against a star in orbit (one was identified last year, in a nine-hour flame schedule) is not unknown, but the case was not so simple. with ESO 253-G003.
This is because ESO 253-G003 is actually two galaxies in the final stages of fusion, which means there should be two supermassive black holes in the center.
Recent research has shown that two interacting supermassive black holes can cause repeated outbreaks, but it is believed that objects in the center of ESO 253-G003 are too far apart to interact in this way.
Another possibility raised was a star that crashed through a disk of material accretion swirling around and feeding into one of the black holes. This also had to be ruled out. When the star crashed across the disk at different locations and angles, the shapes of its flares should have been different, but observations showed that the flares in ESO 253-G003 were too evenly matched.
The third possibility was repeated partial perturbation of the tides, where a larger massive object repeatedly removes material from a smaller orbit.
If a star were in an eccentric 114-day orbit around the black hole, its approach, or periastron, could be seen spinning close enough to cause the material to be stripped before it came out again.
When this material collides with the accretion disk, it causes a flame. And that’s what seems to be happening.
With this scenario in mind, the team analyzed the observations. They analyzed the light curve of each flare and also compared them with other known black hole tidal outage events. And they determined that the star probably orbited a supermassive black hole that had 78 million solar masses.
On each closer approach, the star lost about 0.3 percent of the Sun’s mass (about three Jupiters) to the black hole would be enough to cause the observed flares while allowing the star to live.
“If a giant star with a wrapped envelope wanders nearby, but not too close, in a very elongated orbit, the black hole can steal some of the outer material without tearing the entire star.” said astronomer Benjamin Shappee of the University of Hawaii Institute of Astronomy. “In that case, the giant star will keep coming back again and again until it runs out.”
It is not clear how long the star and the black hole hold this dance, making it difficult to calculate how much time the star has left. But the team has predicted when the next two flares will occur – April and August this year – and they plan to make even more observations.
It represents an extremely rare opportunity to understand the massive accretion of supermassive black holes.
“Overall, we want to understand the properties of these black holes and how they grow,” said astronomer Kris Stanek of Ohio State University. “The ability to predict exactly when the next episode will allow us to take data that we might not otherwise be able to take, and we are already taking it.”
The research was presented at the 237th meeting of the American Astronomical Society. It will also be sent to The Astrophysical Journal, and is available at arXiv.