Free Astronomy Magazine March-April 2023

23 ASTRO PUBLISHING time. This is really unfortunate be- cause there’s a lot of information that you can get from the ultraviolet spectra,” said Emily Engelthaler of the Center for Astrophysics | Harvard & Smithsonian (CfA) in Cambridge, Massachusetts. “We’re excited be- cause 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 taking place on the order of days or months. For any given galaxy with a quies- cent supermassive black hole at the center, it’s estimated that the stellar shredding happens only a few times in every 100,000 years. This AT2022- dsb stellar snacking event was first caught on March 1, 2022 by the All- Sky Automated Survey for Super- novae (ASAS-SN or “Assassin”), a network of ground-based telescopes that surveys the extragalactic sky roughly once a week for violent, variable, and transient events that are shaping our universe. This ener- getic collision was close enough to Earth and bright enough for the Hubble astronomers to do ultravio- let spectroscopy over a longer than normal period of time. “Typically, these events are hard to observe. You get maybe a few ob- servations at the beginning of the disruption 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 hap- pens,” said Peter Maksym of the CfA. “We saw this early enough that we could observe it at these very in- tense black hole accretion stages. We saw the accretion rate drop as it turned to a trickle over time.“ The Hubble spectroscopic data are 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 is swirling around a black hole in the middle. T his sequence of artist’s illustrations shows how a black hole can de- vour a bypassing star. 1−A normal star passes near a supermassive black hole in the center of a galaxy. 2−The star’s outer gasses are pulled into the black hole’s gravitational field. 3−The star is shredded as tidal forces pull it apart. 4−The stellar remnants are pulled into a donut-shaped ring around the black hole, and will eventually fall into the black hole, unleashing a tremendous amount of light and high-energy radi- ation. [NASA, ESA, Leah Hustak (STScI)] ! tected by astronomers using various telescopes. NASA recently reported that several of its high-energy space observatories spotted another black hole tidal disruption event on March 2021, and it happened in another galaxy. Unlike Hubble observations, data was collected in X-ray light from an extremely hot corona around the black hole that formed after the star was already torn apart. “However, there are still very few tidal events that are observed in ul- traviolet light given the observing