An unusually close look at a black hole devouring a passing star

Cairo – Samia Sayed – In March 2021, a star was seen in a galaxy 250 million light years away having a terrible, really bad day, according to RT.

And it was there by itself energetic, pulled into the gravitational well of a supermassive black hole and torn apart into tiny pieces. We know this because many telescopes have captured its view from Earth, as the light from the event streaked across the universe, the the fifth-closest known event of its kind. Since the tidal disturbance event has ever been captured, the wealth of data obtained may help scientists better understand how black holes “feed”.

“Tidal disturbance events are a kind of cosmic laboratory. They are our real-time window into how a supermassive black hole lurking at the center of a galaxy is fueled,” says astronomer Sophie Jezari of the Space Telescope Science Institute.

Tidal disruption events are quite rare, but we’ve seen enough of them to get a fairly detailed understanding of what happens when a star passes in front of a black hole. Once the star is trapped in the black hole’s gravitational field, tidal forces stretch and drag it to the point where it “bumps” (that’s the “turbulence” part).

Then the bowels of the star rush around the black hole in a chaotic manner, its fragments collide with each other and generate shocks that shine at multiple wavelengths. This process isn’t instantaneous, but could take weeks or months as the black hole gobbles up stellar debris.

The debris forms a disk that orbits the black hole, falling (or “piling up”) onto it from the inner edge. When matter falls into a black hole, a structure called a halo can form between the inner edge of the accretion disk and the black hole’s event horizon.

This is a region containing extremely hot electrons that are thought to be powered by the black hole’s magnetic field, which acts like a synchrotron to accelerate the electrons to such high energies that they glow at X-ray wavelengths.

Then powerful jets of plasma shoot out of the black hole’s polar regions, shooting halo material in opposite directions, sometimes at nearly the speed of light. These astrophysical jets are thought to form when matter accelerates along magnetic field lines outside the black hole’s event horizon; When you reach the poles, they explode.

Jets are not observed in all tidal disturbance events, but when they do occur, they are usually seen together. Then, when the transiting Zwicky facility captured a bright flash of the tidal disturbance event on March 1, 2021, later dubbed AT2021ehb, NASA transformed its NICER X-ray Observatory and Rapid Observatory (X-ray , gamma rays and ultraviolet) to monitor the development of the event in the hope of catching something of interest. Later, 300 days after Zwicky’s discovery, the NuSTAR X-ray Observatory joined.

X-ray, ultraviolet, optical and radio radiation emitted by the event over a period of 430 days revealed that the culprit was a black hole about 10 million times the mass of the sun.

But, well, something was off. None of the observers detected any hint of jets. However, NuSTAR observations have revealed the presence of a corona. Scientists say this strange discrepancy is very interesting.

“We’ve never seen an X-ray emitting tidal disturbance event like this without a jet, and that’s really amazing because it means we can separate what causes the jets and what causes the halo,” says the astronomer. Yuhan Yao of Caltech. AT2021ehb’s observations are consistent with the idea that magnetic fields have something to do with how the corona forms, and we want to know what makes this magnetic field so strong.”

Targets like AT2021ehb are excellent laboratories for studying the formation and evolution of accretion disks and coronae in real time; And where there is one, there may be others. The researchers hope they can find more tidal disturbance events in the future, which will lead to answers about the role magnetic fields play in corona formation. A bad day for a star 250 million years ago ended up being a very good day for human astronomers.