(ORDO NEWS) — Back in March 2021, a star in a galaxy 250 million light-years away had a terrible, terrible, no good, really very bad day.
Here she is, minding her own business as he is sucked into the gravity well of a supermassive black hole and blown to smithereens.
This is the fifth largest event known as tidal disruption ever recorded, and the sheer amount of data could help scientists better understand how black holes feed.
“Tidal disruption is a kind of space laboratory,” says astronomer Suvi Gezari of the Space Telescope Science Institute.
“They are our real-time window into which the massive black hole lurking at the center of the galaxy is fed.”
Tidal disruptions are fairly rare, but we’ve seen enough of them to provide a fairly detailed understanding of what happens when a star gets too close to a black hole.
Once a star enters the black hole’s gravitational field, tidal forces stretch and pull it to the point where it breaks apart (this is part of the “destruction”).
The guts of the dismembered star then flow around the black hole in a chaotic pattern, colliding with itself and creating impacts that glow at multiple wavelengths.
This process is not instantaneous, it can take weeks or months as the black hole devours the stellar debris.
Debris forms a spinning disk around the black hole, falling (or “merging”) onto it from its inner edge.
As material falls into the black hole, a structure called a corona can form between the inner edge of the accretion disk and the black hole’s event horizon.
This is a region of hot electrons, supposedly powered by the black hole’s magnetic field, which acts like a synchrotron, accelerating electrons to such high energies that they glow brightly in the X-rays.
Powerful jets of plasma are then ejected from the black hole. polar regions, ejecting corona material in opposite directions, sometimes at nearly the speed of light.
These astrophysical jets are thought to form when material is accelerated along magnetic field lines outside the black hole’s event horizon; when it reaches the poles, it explodes.
Coronas and jets are not seen in all cases of tidal disturbances, but when they occur, they are usually seen together.
So when the Zwicky Transient Facility captured the bright flash of a tidal disruption event, later named AT2021ehb, on March 1, 2021, NASA sent its NICER X-ray Observatory and the Swift Observatory (X-ray, gamma, and ultraviolet) to observe the evolution of the event in the hope of capturing something interesting.
Later, 300 days after Zwicky’s discovery, the NuSTAR X-ray Observatory joined in the fun.
X-ray, ultraviolet, optical and radio emission emitted by the event over a period of 430 days showed that the culprit was a black hole with a mass about 10 million times that of the Sun. It’s okay for now.
But something was strange. None of the observatories found a hint of jets. However, NuSTAR observations revealed the presence of a corona. And this strange discrepancy, according to scientists, is extremely interesting.
“We’ve never seen X-ray tidal disruption like this without the presence of a jet, and that’s really impressive because it means we can potentially separate what causes jets and what causes coronas,” says astronomer Johan. Yao from the California Institute of Technology.
“Our observations of AT2021ehb are consistent with the idea that magnetic fields have something to do with how the corona forms, and we want to know what causes such a strong magnetic field.”
Targets such as AT2021ehb are excellent laboratories for studying the formation and evolution of accretion disks and coronas in real time; and where there is one, there may be more.
The researchers hope that in the future they will be able to find more of these tidal disruption events, leading to answers to the question of the role of magnetic fields in the formation of coronas and jets.
A bad day for a star 250 million years ago was a very, very good day for human astronomers.
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