Astronomers watched as a black hole ripped apart a star, but surprisingly little was eaten

(ORDO NEWS) — What happens when a star gets too close to a supermassive black hole? The obvious story is that he gets sucked in and is never seen again. Some of its material is superheated on the way in, and this emits a huge amount of radiation – usually X-rays. This is not an incorrect explanation, it is simply incomplete.

There’s more to this story, thanks to a team of astronomers at the University of California, Berkeley. They used a specialized spectrograph at the Lick Observatory to study tidal disruption. It was there that the star collided with the black hole. What they found was amazing.

Watching the doomed star drift away

Supermassive black holes have been found in galaxies throughout the universe. When a star approaches it, strange things happen. The gravitational pull tears the star apart and stretches out some of its material in a process called “spaghettification”.

Recent studies of tidal disruption suggest other things are happening as well. For example, strong winds blowing away from the scene send some of the doomed star’s material into space. It’s all part of her weirdness.

“One of the craziest things a supermassive black hole can do is rip apart a star with its massive tidal forces,” said team member Wenbin Lu, assistant professor of astronomy at UC Berkeley. .

“These stellar tidal disruptions are one of the very few ways astronomers know about the existence of supermassive black holes at the centers of galaxies and measure their properties. events, astronomers still do not understand the complex processes after tidal disruption.”

That is why it is so important to study the real star at the time of her death. The Berkeley team targeted one that got too close to the black hole during an event called “AT2019qiz”.

The crash occurred about 215 million light-years from Earth in a spiral galaxy in the constellation Eridani. . As the star spiraled into the accretion disk, it exploded into pieces.

Then something completely unexpected happened. And it took a special effort to see it.

Polarized view of action

After the destruction event looked quite bright in optical light, the team members decided to study it in polarized light to better understand what was going on. Polarized light waves propagate in a single plane, which reduces the light intensity. (The same principle is used in polarized sunglasses to reduce glare.)

In this case, the use of polarized light allowed the team to see the effects of the star’s destruction. Usually they don’t see it. Based on observations of other similar events, they also did not see the expected amount of X-rays. So what’s going on?

For AT2019qiz, spectropolarimetric observations have shown that much of the star’s material never made it into the black hole’s hungry mouth. Some are scattered throughout the space.

However, strong winds from the black hole also created a spherically symmetric high-speed cloud of the remaining stellar material. The team accelerated it to a speed of about 10,000 kilometers per second. This cloud definitely held some surprises.

“This is the first time anyone has determined the shape of a gas cloud around a star that has undergone tidal spaghettization,” said Alex Filippenko, a professor of astronomy at the University of California at Berkeley and a member of the research team. Research group.

Crushed Star gives clues to similar events

This unique view of star breakup explains why astronomers haven’t seen much high-energy X-rays from this and other similar tidal breakup events. The strong winds created the cloud, and it blocks most of the high-energy radiation from collapsing.

“People have seen other evidence that the wind is coming from these events,” said Koshore Patra, a researcher. graduate student and lead author of the study.

“I think this polarization study definitely makes this evidence more convincing in the sense that you can’t get a spherical geometry without enough wind. The interesting thing is that a significant part of the matter of the star, which spirals inwards, eventually does not fall into the black hole, but is blown out of the black hole.”

What’s next?

The use of polarized light provides an important tool for studying what happens when other stars collide with supermassive black holes. It also gives astronomers access to events in the black hole’s accretion disk. This is not an easy task.

“These destruction events are so far away that you cannot really resolve them, so you cannot study the geometry of the event or the structure of these explosions,” Filippenko. indicated.

“But studying polarized light actually helps us get some information about the distribution of matter in this explosion or, in this case, how the gas and possibly the accretion disk around this black hole is formed.”

Polarized light from these types of bright “eruptions” is a valuable tool for mapping these events. Ultimately, such observations could help build a “tomographic” picture of a tidal disruption event as it unfolds, even if it occurs in a galaxy far, far away.


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