A study reveals the final fate of a star torn through a black hole

In 2019, astronomers observed the closest example yet of a starburst, or “spaghetti crash,” after coming very close to a supermassive black hole.

This tidal disturbance of a solar star through a black hole that is a million times larger than it occurred, according to an RT report, 215 million light-years from Earth in the spiral galaxy River Constellation.

Fortunately, this was the first event so bright enough that astronomers at the University of California, Berkeley, could study the optical light of stars dead, specifically the polarization of light, to find out more about what happened after the star burst. has.

Observations on October 8, 2019 indicate that many of the star’s material exploded at high speed – up to 10,000 kilometers per second – and formed a spherical cloud of gas that blocked most of the resulting high-energy emissions. , as the remaining black hole was digested. of the star.

Earlier, other observations of the optical light of the explosion, dubbed AT2019qiz, revealed that much of the star’s material was blown outward by strong winds, but the new data on the polarization of light, which was essentially zero at visible or optical wavelengths. , when the event was at its peak, astronomers say the cloud was probably spherically symmetrical.

“This is the first time anyone has inferred the shape of a gas cloud around a star that has experienced a spaghetti impact,” said Alex Filippenko, a professor of astronomy at the University of California, Berkeley and a member of the research team said. due to its strong gravitational field).

The results support one answer as to why astronomers have not seen high-energy radiation, such as X-rays, from many of the tidal disturbance events observed so far: X-rays, which are produced by shredded material of the star. It is pulled into a disk that pulls up around the black hole before falling inward, blocked by the outward blown gas by strong winds from the black hole.

Kishore Batra, a graduate student at the University of California, Berkeley, lead author of the study, explained: “This observation excludes a class of solutions that have been proposed theoretically and gives us stronger constraints on what happens to the gas around the black People have seen other evidence of winds coming from these events, and I think this study of polarization certainly makes this evidence stronger, in the sense that you will not get a spherical geometry without enough wind. The interesting fact here is that a large part of the matter in the star spiraling inwards does not eventually fall into the black hole, it explodes away from it. “

Polarization reveals symmetry

Many theorists have assumed that the stellar debris forms an eccentric and asymmetric disk after perturbation, but the eccentric disk is expected to exhibit a relatively high degree of polarization. It was not observed due to the tidal disturbance.

“One of the craziest things a supermassive black hole can do is rip a star apart by massive tidal forces,” said team member Wenbin Lu, an associate professor of astronomy at the University of California, Berkeley. very few ways they are known “Astronomers find supermassive black holes at the centers of galaxies and measure their properties. Given the high computational cost of digitally simulating such events, astronomers still do not understand the complex processes following tidal disruption.”

A second set of observations on November 6, 29 days after the October observation, revealed that the light was very slightly polarized, about 1%, indicating that the cloud had weakened enough to form the asymmetric gas structure around the black hole. to reveal.

Both observations came from the 3-meter Shin telescope at the Lake Observatory near San Jose, California, which is equipped with the Kast spectrometer, an instrument that can determine the polarization of light across the full optical spectrum. Light is polarized – its electric field vibrates essentially in one direction – when electrons are scattered in the gas cloud.

“The scavenger disk itself is hot enough to emit most of its light in X-rays, but that light must come through this cloud, and there is a lot of scattering, absorption and re-emission of light before it can escape from this cloud,” said Batra. “The light loses its photon energy, goes to the ultraviolet and optical energy. Then the final scattering determines the photon’s polarization state. So, by measuring the polarization, we can derive the geometry on the surface where the final scattering takes place.”

The UC Berkeley researchers calculated that polarized light is emitted from the surface of a spherical cloud with a radius of about 100 astronomical units (au), which is 100 times farther from the star than the earth from the sun is. An optical glow of hot gas coming from a region at about 30 AU.

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