By | November 20, 2022
Hubble finds hungry black holes twisting the trapped star into a doughnut shape

Hubble finds hungry black holes twisting the trapped star into a doughnut shape

This sequence of artist’s illustrations shows how a black hole might swallow a passing star. 1. A normal star passes close to a supermassive black hole at the center of a galaxy. 2. The star’s outer gases are pulled into the black hole’s gravitational field. 3. The star is torn apart as tidal forces pull it apart. 4. The stellar debris is drawn into a donut-shaped ring around the black hole, and will eventually fall into the black hole, releasing an enormous amount of light and high-energy radiation. Credit: NASA, ESA, Leah Hustak (STScI)

Black holes are gatherers, not hunters. They lie in wait until an unlucky star wanders by. When the star gets close enough, the black hole’s gravitational grip violently tears it apart, carelessly gobbling up its gases while belching out intense radiation.

Astronomers using NASA’s Hubble Space Telescope have recorded a star’s final moments in detail as it is swallowed by a black hole.

These are called “tidal disturbance events”. But the wording belies the complex, raw violence of a black hole encounter. There is a balance between the black hole’s gravity pulling in stellar material and radiation blowing material out. In other words, black holes are fussy eaters. Astronomers are using Hubble to find out the details of what happens when a wayward star plunges into the gravitational abyss.

Hubble is unable to photograph the tidal event AT2022dsb up close because the dwarf star is nearly 300 million light-years away in the core of the galaxy ESO 583-G004. But astronomers used Hubble’s powerful ultraviolet sensitivity to study the light from the shredded star, which includes hydrogen, carbon and more. The spectroscopy provides forensic clues to the black hole murder.

About 100 tidal disturbances around black holes have been discovered by astronomers using various telescopes. NASA recently reported that several of its high-energy space observatories detected another tidal disruption event in the black hole on March 1, 2021, and it happened in another galaxy. Unlike Hubble observations, the data were collected in X-ray light from an extremely hot corona around the black hole that formed after the star had already been torn apart.

“However, there are still very few tidal events observed in ultraviolet light considering the observation time. This is really unfortunate because there is a lot of information that you can get from the ultraviolet spectra, says Emily Engelthaler of the Center for Astrophysics | Harvard & Smithsonian (CfA) in Cambridge, Massachusetts. “We’re excited because we can get these details about what the debris is doing. The tidal event can tell us a lot about a black hole.” Changes in the state of the doomed star take place on the order of days or months.

For a given galaxy with a quiescent supermassive black hole at its center, it is estimated that star disintegration occurs only a few times every 100,000 years.

This AT2022dsb stellar snacking event was first captured on March 1, 2022 by All-Sky Automated Survey for Supernovae (ASAS-SN or “Assassin”), a network of ground-based telescopes that survey the extragalactic sky about once a week for violent, variable, and transient events that shape our universe. This energetic collision was close enough to Earth and bright enough for the Hubble astronomers to perform ultraviolet spectroscopy for a longer time than normal.

“Usually these events are hard to observe. You might get a few observations at the beginning of the disturbance when it’s really bright. Our program is different in that it’s designed to look at a few tidal events over the course of a year to see what happens,” said Peter Maksym from CfA. “We saw this early enough that we could observe it at these very intense black hole accretion stages. We saw the accretion rate drop as it turned to a trickle over time.”

Hubble’s spectroscopic data are interpreted as coming from a very bright, hot, doughnut-shaped region of gas that was once the star. This region, known as a torus, is the size of the solar system and swirls around a black hole at its center.

“We’re looking somewhere on the edge of the donut. We see one star wind from the black hole sweeping across the surface projected toward us at speeds of 20 million miles per hour (three percent of the speed of light), Maksym says. You shred the star and then it has this material that goes into the black hole. And then you have models where you think you know what’s going on, and then you have what you actually see. This is an exciting place for scientists to be: right at the interface between the known and the unknown.”

The results were reported at the 241st meeting of the American Astronomical Society in Seattle, Washington.

More information:

Quote: Hubble finds hungry black holes twisting captured star into donut shape (2023, January 13) retrieved January 13, 2023 from

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