NASA gets an unusually close look at a black hole nibbling a star

NASA gets an unusually close look at a black hole snacking on a star

In this image, a disk of hot gas swirls around a black hole. Some of the gas came from a star that was being pulled apart by the black hole, forming the long stream of hot gas on the right that poured into the disk. These events are officially known as tidal disturbance events, or TDEs. From the destruction of the star to the formation of the disk, it can take as little as one thing, or weeks, or months. The gas gets hotter the closer it gets to the black hole, but the hottest material is above the black hole. This hottest material is a cloud of plasma (gas atoms stripped of their electrons) known as the corona. Most TDEs that lead to the formation of a corona also produce jets of material that are ejected into space away from the black hole at its poles. A TDE named AT2021ehb is the first confirmed example of nozzle-less corona formation in a tidal disturbance event. The observation of AT2021ehb allows the scientists to study the formation of jets and coronae separately. Credit: NASA/JPL-Caltech

Recent observations of a black hole devouring a wandering star could help scientists understand the more complex black hole feeding behavior.

Several NASA telescopes recently observed a massive black hole tear apart an ill-fated star that wandered too close. Located about 250 million light-years from Earth at the center of another galaxy, it was the fifth closest example of a black hole destroying a star ever observed.

After the star was thoroughly ruptured by the black hole’s gravity, astronomers saw a dramatic increase in high-energy X-ray light around the black hole. This indicated that as the stellar material was being drawn toward its demise, it formed an extremely hot structure called the corona over the black hole.

NASA’s NuSTAR (Nuclear Spectroscopic Telescopic Array) satellite is the most sensitive space telescope capable of observing these wavelengths of light, and the event’s proximity offered an unprecedented look at its formation and, according to a new study published in development of the corona Astrophysical Journal.

The work shows how the destruction of a star by a black hole – a process officially known as a tidal disturbance event – could be used to better understand what happens to material captured by one of these giants before it is fully engulfed will.

Most black holes that scientists can study are surrounded by hot gas that has accumulated over many years, sometimes millennia, to form disks billions of kilometers wide. In some cases, these discs shine brighter than entire galaxies. Even around these bright sources, but especially around much less active black holes, a single star is striking, being torn apart and consumed.

And from start to finish, the process often only takes weeks or months. The observability and short duration of tidal disturbances make them particularly attractive to astronomers, who can figure out how the black hole’s gravity manipulates the material around it, creating incredible light shows and new physical features.

“Tidal disturbances are a kind of cosmic laboratory,” said study co-author Suvi Gezari, an astronomer at the Space Telescope Science Institute in Baltimore. “They are our window into real-time feeding of a massive black hole lurking at the center of a galaxy.”

When a star gets too close to a black hole, strong gravity stretches the star until it becomes a long stream of hot gas, as shown in this animation. The gas is then whipped around the black hole and gradually pulled into orbit, creating a bright disk. Picture credits: Laboratory for Science Communication/DESY

A surprising sign

The new study focuses on an event called AT2021ehb, which took place in a galaxy with a central black hole about 10 million times the mass of the Sun (about the difference between a bowling ball and the Titanic). During this tidal disturbance event, the side of the star closest to the black hole was pulled more than the other side of the star, pulling the whole thing apart, leaving nothing but a long noodle of hot gas.

Scientists believe that in such events, the gas stream whips around a black hole and collides with itself. This is thought to create shock waves and outward gas flows that produce visible light, as well as wavelengths invisible to the human eye, such as ultraviolet light and X-rays. The material then settles into a disk that spins around the black hole like water orbiting a drain, with friction producing low-energy X-rays. In the case of AT2021ehb, this series of events lasted only 100 days.

The event was first detected on March 1, 2021 by the Zwicky Transient Facility (ZTF) at the Palomar Observatory in Southern California. It was subsequently studied by Neil Gehrel’s Swift Observatory and NASA’s Neutron Star Interior Composition Explorer (NICER) telescope (which observes longer X-ray wavelengths than Swift).

Then, about 300 days after the event was first spotted, NASA’s NuSTAR began observing the system. Scientists were surprised when NuSTAR detected a corona – a cloud of hot plasma or gas atoms that have had their electrons stripped – since coronas usually appear with jets of gas pouring out of a black hole in opposite directions.

However, there were no jets at the AT2021ehb tidal event, making the corona observation unexpected. Coronas emit higher-energy X-rays than any other part of a black hole, but scientists don’t know where the plasma comes from or exactly how it gets so hot.

“We’ve never seen an X-ray emission tidal disturbance event like this without a jet, and it’s really spectacular because it means we can potentially unravel what’s causing jets and what’s causing coronae,” said Yuhan Yao, a graduate student at Caltech in Pasadena , California, and lead author of the new study. “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 is causing this magnetic field to become so strong.”

Yao is also leading efforts to look for other tidal disturbances identified by the ZTF and then observe them with telescopes such as Swift, NICER and NuSTAR. Each new observation offers the potential for new insights or ways to confirm what has been observed in AT2021ehb and other tidal disturbances. “We want to find as many as possible,” Yao said.

More information:
Yuhan Yao et al, The Tidal Disruption Event AT2021ehb: Evidence of Relativistic Disk Reflection, and Rapid Evolution of the Disk-Corona System, The Astrophysical Journal (2022). DOI: 10.3847/1538-4357/ac898a

Provided by Jet Propulsion Laboratory

Citation: NASA Receives Unusually Close View of Black Hole Snacking on Star (2022, December 20) Retrieved December 21, 2022 from -black-hole.html

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