Black holes often sit at the centres of galaxies, where they can gorge themselves on the superheated material that falls into their abyssal event horizons. Now, a team of astronomers have observed the beginning of one such meal.
The feast was found in a galaxy a staggering 10 billion light-years from Earth. The meal itself — or what the astronomers think is a black hole’s meal — is a luminous transient, meaning an object that changes in brightness quickly. It was first discovered in 2019 and is called J221951-484240 (J221951 for short.)
To date, the event has been observed by the Swift Observatory, the Hubble Space Telescope, the South African Large Telescope, and ESO observatories including the Very Large Telescope.
The astronomers studying the object believe it was caused by one of two events; either a star passed too close to the black hole, and the latter ripped material away from the former, or a dormant black hole at the centre of its galaxy suddenly began feeding. The team’s research is set to publish in the Monthly Notices of the Royal Astronomical Society and is currently hosted on the preprint server arXiv.
“J221951 is one of the most extreme examples yet of a black hole taking us by surprise,” said Matt Nicholl, an astronomer at Queen’s University Belfast and a co-author of the research, in an Royal Astronomical Society release. “Continued monitoring of J221951 to work out the total energy release might allow us to work out whether this is a tidal disruption of a star by a fast-spinning black hole, or a new kind of AGN switch on.”
AGN, an acronym for active galactic nuclei, have jet- and wind-emitting supermassive black holes at their cores. An ultraviolet spectrum of the object suggested to the research team that material was pushed outwards by some energetic outburst. A black hole suddenly deciding to feed could effectively “switch on” a galactic nucleus, and may be the situation at play in J221951.
Tidal disruption events occur when a star passes close — too close — to a black hole, causing it to yield at least some of its material to the abyss. But often, the black hole’s intense gravity pulls the entire star apart, an event called spaghettification.
Once spaghettified, the stellar material tends to orbit the black hole, rather than being swept immediately into the inky black. The orbiting stellar material heats up, allowing astronomers to detect the event. Last year, astronomers even found a black hole that did the cosmic equivalent of chundering when it puked up stellar material that it consumed at least three years earlier.
“In the future we will be able to obtain important clues that help distinguish between the tidal disruption event and active galactic nuclei scenarios,” said Samantha Oates, an astronomer at the University of Birmingham and the new study’s lead author, in the same release. “For instance, if J221951 is associated with an AGN turning on we may expect it to stop fading and to increase again in brightness, while if J221951 is a tidal disruption event we would expect it to continue to fade.”
“We will need to continue to monitor J221951 over the next few months to years to capture its late-time behaviour,” Oates added.
Black holes only have a vacant demeanour if you peer into their lightless shadows. Observing their effects on surrounding matter reveals that black holes are some of the most dynamic objects in the universe. Just this week, astronomers using the Webb Space Telescope announced the discovery of the most distant active supermassive black hole, which dates back to around 570 million years after the Big Bang.
Whether it was an unfortunate star or a hungry, hungry hole — or both! — in J221951, the truth may help astronomers understand black hole behaviour, and the sort of conditions that might cause such a behemoth to suddenly decide to “eat.”
The cosmos has plenty of many mysteries strewn across space and time. With just a few telescopes and some more observations, astronomers might clarify what went down in that ancient galaxy some 10 billion light-years away.
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