Astronomers observed a star that was shredded after it was too close to a black hole.
It took place 215 million light years away from Earth. Astronomers from the University of California, Berkeley were able to study the light from the stellar death to learn more about what happened after it was torn apart.
A lot of the star's material was blown away at high speed, forming a spherical cloud of gas that blocked most of the high-energy emissions produced as the black hole devoured the rest of the star.
The star's matter was blasted out in a powerful wind by the blast. The new data shows that the light was essentially zero at visible or optical wavelength when the event was at its peak.
Alex Filippenko is a professor of astronomy and a member of the research team.
The X-rays, which are produced by material ripped from the star and dragged into an accretion disk around the black, are not visible to the naked eye.
"This observation rules out a class of solutions that have been proposed theoretically and gives us a stronger constraint on what happens to gas around a black hole," said UC Berkeley graduate student. "People have been seeing other evidence of wind coming out of these events, and I think this study definitely makes that evidence stronger, in the sense that you wouldn't get a spherical geometry without having a sufficient amount of wind" A significant portion of the star's material doesn't fall into the black hole, but is blown away from it.
Symmetric is revealed by polarization.
According to many theorists, the stellar debris forms an eccentric, asymmetric disk after disruption, but an eccentric disk is expected to show a relatively high degree of polarisation. This wasn't observed for the event.
One of the craziest things a black hole can do is to destroy a star. Calculating the properties of black holes at the centers of galaxies is one of the few ways that astronomy knows about them. Astronomers don't understand the complicated processes after a tidal disruption due to the high cost of simulations.
A second set of observations on Nov. 6, 29 days after the October observation, showed that the light was very close to the black hole. The observations were made from a 3-meter telescope at Lick Observatory near San Jose, California, that is fitted with an instrument that can determine the wavelength of light. The light's electrical field vibrates in one direction when it hits the gas cloud.
The accretion disk is hot enough to emit most of its light in X-rays, but that light has to come through this cloud and there are many scatterings, absorptions and reemissions of light before it can escape out of this cloud The light goes all the way down to ultraviolet and optical energies with each process. The state of the photon is determined by the last scatter. The geometry of the surface can be deduced by measuring polarization.
The deathbed scenario may only apply to normal tidal disruptions, not oddballs, in which jets of material are ejected out the poles of the black hole. The question will only be answered by more measurement of the light's intensity.
Few people are well-versed enough in the technique around the world to use polarization studies. This is a new area for tidal disruption events.
A group of people have reported their observations in a paper that has been accepted for publication in a journal.
The cloud is 100 times bigger than Earth's.
The researchers at UC Berkeley calculated that the light from the cloud was 100 times farther away from the star than the sun is. A glow from hot gas was visible.
There was a tidal disruption event located in a spiral galaxy in the constellation of Eridanus. A spherically symmetric cloud of gas can be seen in the October spectrum. The November measurement shows a small discrepancy. In the centers of distant galaxies, the tidal disruptions appear as a point of light and are not indicative of the shape of objects.
Filippenko said that the geometry of the event or the structure of the explosions can't be studied because they are so far away. We can deduce some information about the distribution of the matter in that explosion or, in this case, how the gas around this black hole is shaped, by studying the light that's reflected from it.
More information: Kishore C Patra et al, Spectropolarimetry of the tidal disruption event AT 2019qiz: a quasispherical reprocessing layer, Monthly Notices of the Royal Astronomical Society (2022). DOI: 10.1093/mnras/stac1727 Journal information: Monthly Notices of the Royal Astronomical Society
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