The captured star has had several close encounters with supermassive black holes in distant galaxies – and may even have escaped material being torn apart by its massive gravitational tidal forces.
destroy a bintang by the gravitational force of Giant black hole This is a violent event known as a Tidal Distance Event (TDE). Gas is snatched from the star and undergoes a process of “spagitation,” in which it is slashed and stretched into a stream of hot material that flows around it. Black hole, forming a very bright and transient accretion disk. From our point of view, center galaxy Supermassive black holes appear to glow.
On September 8, 2018, the All-Sky Automated Survey for Supernovae (ASASSN) detected light in the core of a distant galaxy 893 million light years away. The flare is classified as AT2018fyk, and has all the advantages of the TDE. Various X-ray telescopes, including the NASA telescope Fastin Europe XMM-Newtonthat Very nice Instruments aboard the International Space Station, Germany AerositaNotice that the black hole is shining brightly. Typically, TDEs show a subtle dip in brightness over several years, but when astronomers looked back at AT2018fyk about 600 days after it was first observed, the X-rays quickly faded away. Even more confusing, 600 days after that, the black hole suddenly erupted again. What happened?
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“Until now, the assumption was that when we looked at the results of a close encounter between a star and a supermassive black hole, the results would be fatal for the star; that is, the star completely disintegrates,” said Thomas Weavers, an astronomer at the European Southern Observatory and author of new research on the event. , he statement. “But unlike all the other TDEs we know of, when we pointed our telescopes at the same locations again several years later, we found they had returned to light.”
Wevers led a team of astronomers who realized that the repeated flare was an asterisk that had survived the TDE and completed another orbit for the second TDE. To fully explain what they observed, Wevers’ group developed the “partially repeated TDE” model.
In their model, the star used to be a member of binary system that passes near the black hole at the center of its galaxy. The black hole’s gravity pushes one of the stars away, and it turns into a runaway Speed star Racing at 600 miles (1,000 km) per second out of the galaxy. Another star becomes tightly bound to the black hole, in a 1,200-day elliptical orbit that takes it toward what scientists call the tidal radius – the distance from the black hole where the star begins to be torn apart by the gravitational tides emanating from the black hole.
Since the star is not within its tidal radius, only some of its material is stripped away, leaving behind a dense stellar core that continues its orbit around the black hole. It takes roughly 600 days for the material the black hole pulls from the star to form an accretion disk, so by the time astronomers see the system’s light, the star is safe, near the furthest point in its orbit.
But when the star’s core begins to approach the black hole again, about 1,200 days after their first encounter, the star begins to take some of its matter back from the accretion disk, causing the X-ray emission to suddenly subside. “When the core returns to the black hole, it essentially steals all the gas from the black hole through gravity, and as a result no matter has accumulated, so the system goes dark,” said co-author Dheeraj Pasham. study and astrophysicists in the journal Science.Massachusetts Institute of Technology, per a statement.
But black holes gravity He quickly returned the favor, and stole more items as the star approached. As was the case during the initial encounter, there is a 600 day lag from the black hole consuming the star to the formation of the accretion disk, which explains why the X-ray glow restarts when it does.
From the orbit of the star, the Wavers team estimated the black hole to be about 80 million times the mass of our Sun, or about 20 times the mass of the black hole at the center of our planet. Milky WayAnd arch *.
The team of weavers didn’t have to wait long to see if the theory holds true. Scientists expect AT2018fyk to darken again in August, when the star’s core ignites again, and to become even brighter in March 2025 when new material begins to accumulate in the black hole.
However, there is a potential complication in how much mass is lost from the star to the black hole. The amount of mass lost depends in part on the rotational speed of the star, which may be affected by the black hole. If the star rotates fast enough to break up, the black hole will easily steal the material, adding to the loss of mass.
“If the mass loss was only at a rate of 1%, we would expect the star to survive more encounters, whereas if it was closer to 10%, the star may have disintegrated,” Eric Coughlin, a co-author on the study from Syracuse University in New York, said in a statement. that.
Regardless, partial and repeated TDEs provide a rare window into the life of supermassive black holes that we normally can’t detect because they are asleep. This is important for measuring their mass and determining something about how black holes evolve, and then how the galaxies around black holes also evolve throughout cosmic history.
The results were presented at the 241st meeting of the American Astronomical Society and published in Astrophysics Journal Letterboth on Jan. 12.
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