About every 114 days, almost like a clock, a galaxy 570 million light-years away lights up like fireworks. Since at least 2014, 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 orbited by a star that, every 114 days, swings close enough for some of its material to be left upward, causing a bright light length multiple wave. He then moves away, surviving to be left again at the next approach.
Due to the regularity of the rockets, astronomers have nicknamed the galaxy “Old Faithful”, as well as the geyser in Yellowstone National Park.
“These are the most predictable and frequent recurring frequencies with multiple wavelengths we have seen from the core of a galaxy and give us a unique opportunity to study in detail this ancient extragalactic believer,” said the study’s first author, the astronomer. Anna Payne from the University of Hawai’i at Mānoa.
“We believe that a supermassive black hole in the center of the galaxy creates explosions because it partially consumes a giant orbiting star.”
The flames were first detected in November 2014, taken over by the All-Sky Automated Survey for Supernovae (ASAS-SN). At the time, astronomers believed that glow was a supernova that appeared in ESO 253-G003.
But in 2020, when Payne looked at ASAS-SN data on ESO 253-G003, he found another eruption from the same location. And another. And another.
In total, she identified 17 missiles, spaced about 114 days apart. She and her team then predicted that the galaxy would overflow again 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 that they were able to make new, more detailed observations of the May flame with NASA’s powerful TESS telescope. Previous observations from other instruments have also provided data on a range of wavelengths.
“TESS provided a very detailed picture of that flame, but because of the way the mission imagines the sky, it can’t see them all,” said astronomer Patrick Vallely of Ohio State University. “ASAS-SN collects less detail about individual outbreaks, but provides a longer baseline, which was crucial in this case. The two surveys complement each other.”
But a supernova ignites only once, then fades, because such an event destroys the original star; so whatever caused light eruptions in optical, ultraviolet, and X-ray wavelengths had to be something else.
A supermassive black hole that emits ordinary flares as it tastes on an orbiting star is unheard of – one was identified last year in a nine-hour flare program – but the case was not as simple with ESO 253- G003.
That’s because ESO 253-G003 is actually two galaxies in the final stages of fusion, which means there should be two supermassive black holes at its center.
Recent research has shown that two interacting supermassive black holes can cause repeated flares, but it is believed that objects in the ESO 253-G003 center are too far apart to interact in this way.
Another high possibility was a star that collapsed through a disk of material accumulation that revolved around it and fed into one of the black holes. This had to be ruled out as well. As the star crashed into the disk at different locations and angles, the shapes of its missiles should have been different – but observations showed that the missiles in ESO 253-G003 were too appropriate.
The third possibility was the repeated partial interruption of the tides, in which a larger massive object repeatedly removes the material from a smaller orbiting one.
If a star was in an eccentric 114-day orbit around the black hole, its close proximity, or periastron, it could see it close enough for the material to be stripped before moving away again.
When this material collides with the accumulation disk, it causes an eruption. And that seems to be happening.
Given this scenario, the team analyzed the observations. They analyzed the light curve of each flame and also compared them with other known tidal disturbance events. And they determined that the star probably orbited a supermassive black hole that revolved at 78 million solar masses.
At each closest approach, the star loses about 0.3 percent of the Sun’s mass – about three Jupiters – to the black hole would be enough to cause observed missiles, while allowing the star to live.
“If a huge star with a fluffy envelope wanders close, but not too close, in a very long orbit, then the black hole can steal some of the outer material without breaking the entire star.” said astronomer Benjamin Shappee of the University of Hawaii’s Institute for Astronomy. “In this case, the giant star will always return until the star runs out.”
It is not clear how long the star and the black hole maintain this dance, which makes it difficult to calculate how long the star remained. But the team predicted when the next two missiles would appear – in April and August this year – and they plan to make even more observations.
It is an extremely rare opportunity to understand the mass accumulation of supermassive black holes.
“In general, we really 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 the exact timing of the next episode allows us to take data that we would not otherwise be able to take, and we are already taking such data.”
The research was presented at the 237th meeting of the American Astronomical Society. It will also be sent to The astrophysics journaland is available on arXiv.