Using the Hubble Space Telescope, astronomers have recorded in detail the final moments of a star when it is engulfed by a black hole.
Black holes are gatherers, not hunters. They lie in wait until a hapless star passes. When the star gets close enough, the black hole’s gravitational grip violently tears it apart and devours its gases while spewing out intense radiation. This is called a ‘tidal disruption event’.
There is a balance between the gravity of the black hole that pulls in the stellar matter and the radiation that pushes the matter out. In other words, black holes are messy eaters. Astronomers are using Hubble to discover the details of what happens when a rogue star plunges into the gravitational chasm.
Hubble is unable to photograph the chaos of the tidal event AT2022dsb up close, as the chewed up star is nearly 300 million light-years away at the center of the galaxy ESO 583-G004. But astronomers used Hubble’s powerful ultraviolet sensitivity to study the shredded starlight, which includes hydrogen, carbon, and more. Spectroscopy provides forensic clues to the black hole homicide.
Astronomers have detected around 100 tidal disruption events around black holes using various telescopes. NASA recently reported that several of its high-energy space observatories detected another black hole tidal disruption event on March 1, 2021, and it happened in another galaxy. Unlike the Hubble observations, the data was collected in X-ray light from an extremely hot corona around the black hole that formed after the star had already torn apart.
“However, there are still very few tidal events that are observed in ultraviolet light given the observation time. This is truly unfortunate because there is a lot of information that can be gleaned from ultraviolet spectra,” Emily Engelthaler of the Center for Astrophysics | Harvard & Smithsonian (CfA). “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 doomed star’s condition are occurring on the order of days or months.
For any given galaxy with a quiescent supermassive black hole at the center, stellar crushing is estimated to occur only a few times every 100,000 years.
This stellar lunch event AT2022dsb was first imaged on March 1, 2022 by the All-Sky Automated Survey for Supernovae (ASAS-SN or “Assassin”). This energetic collision was close enough to Earth and bright enough for Hubble astronomers to do ultraviolet spectroscopy for a longer period of time than normal.
“These events are usually difficult to observe. Maybe you’ll get some observations at the beginning of the outage when it’s really bright. Our program is different in that it is designed to look at a few tidal events over a year to see what happens,” said CfA’s Peter Maksym. “We saw this early enough to be able to observe it in these very intense black hole accretion stages. We saw the accretion rate drop as it became a trickle over time.”
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The Hubble spectroscopic data is interpreted as coming from a very bright, hot, donut-shaped area of gas that was once the star. This area, known as a torus, is the size of the solar system and revolves around a black hole in the middle.
“We are looking somewhere on the edge of that donut. We are seeing a stellar wind from the black hole sweeping across the surface that is projected towards us at speeds of 20 million miles per hour (three percent of the speed of light), Maksim said. “We’re really still thinking about the event. You grind up the star and then you have this material working its way into the black hole.. And so 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: right at the interface of the known and the unknown.”
The results were reported at the 241st meeting of the American Astronomical Society in Seattle. (YO)
Source: Eluniverso
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