Black holes are collectors, not hunters. They are waiting for an unlucky star to pass by. When the star gets close enough, the black hole’s gravitational grip violently rips it apart and sloppily devours its gases while emitting intense radiation.
Astronomers using NASA’s Hubble Space Telescope have recorded in detail a star’s final moments as it is devoured by a black hole.
These are called “tidal disturbance events.” But the phrasing belies the raw, complex violence of black hole encounters. There is a balance between the gravity of a black hole that pulls in stellar objects, and the radiation that blasts away material. In other words, black holes are messy eaters. Astronomers use Hubble to learn the details of what happens when a wayward star sinks into a gravitational abyss.
The Hubble telescope can’t image AT2022dsb’s tidal chaos up close, since the chewed star is about 300 million light-years away in the heart of galaxy ESO 583-G004. But astronomers have used Hubble’s strong ultraviolet sensitivity to study the light from the shattered star, which includes hydrogen, carbon, and more. Spectroscopy provides forensic evidence of black hole killing.
Astronomers have detected about 100 tidal disturbance events around black holes using various telescopes. NASA recently reported that several of its high-energy space observatories detected another black hole tidal disturbance event on March 1, 2021, and it occurred in another galaxy. Unlike the Hubble observations, the data was collected in X-ray light from the superheated halo 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 given the observation time,” said Emily Engelthaler of the Center for Astrophysics. “And that’s really unfortunate because there’s so much information you can get of ultraviolet rays. Harvard and Smithsonian (CfA) in Cambridge, Massachusetts. “We’re excited that we can get these details about what the debris is doing. Tidal events can tell us a lot about a black hole.” Changes in the condition of the stricken star occur in the order of days or months.
For any galaxy with a superquiet black hole at the center, stellar shredding is estimated to only happen a few times every 100,000 years.
This AT2022dsb stellar snack event was first detected on March 1, 2022 by the Instrumental All-Sky Survey of Supernovae (ASAS-SN, or “Assassin”), a network of ground-based telescopes that scans the extragalactic sky roughly once a week in search of About the violence and the changing and transient events that make up our universe. This energetic collision was close enough to Earth and bright enough for Hubble astronomers to do ultraviolet spectroscopy over a longer period of time than usual.
“Normally, these events are hard to notice. You probably get some feedback at the beginning of a disturbance when it’s really bright. Our software is different in that it’s designed to look at some tidal events over the course of a year to see what happens,” said Peter Maxim of CfA. “We’ve seen this. Early enough that we can observe it in the extremely intense phases of black hole accretion. We’ve seen the rate of accumulation decrease as it becomes shortening over time.”
The Hubble spectroscopic data is interpreted as coming from a very bright, hot donut-shaped region of gas that was once a star. This region, known as the ring, is the size of the solar system and orbits a black hole in the centre.
“We’re looking somewhere on the edge of that donut. We see stellar winds from the black hole sweeping across the surface which is being projected toward us at 20 million miles per hour (three percent of the speed of light),” Maxim said. “We’re really still racking our heads around the event. You rip the star apart and then you get this material that makes 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’re actually seeing. That’s an exciting place for scientists to be: the The interface of the known and the unknown.”
The results were reported at the 241st meeting of the American Astronomical Society in Seattle, Washington.
Courtesy of NASA’s Goddard Space Flight Center
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