Insights from a stellar death 215 million light-years from Earth show a black hole blowing the star away—not just sucking it in.
When a black hole “spaghettified” a star in 2019, researchers were watching, allowing them to learn plenty about black holes during the stellar death.
The event leading to the star’s demise—known as a tidal disruption event, this one classified as “AT2019qiz”—happened roughly 215 million light-years from Earth, when the star strayed too close to the black hole. The resulting optical light from the stellar death was bright enough for astronomers from the University of California, Berkeley to fully study for the first time.
The result? About half the star was sucked in, and the other half of the star was powerfully blown out, away from the black hole, and in a spherical symmetry, no less.
“This is the first time anyone has deduced the shape of the gas cloud around a tidally spaghettified star,” Alex Filippenko, a professor of astronomy at UC Berkeley who was involved in the new work, says in a news release. The team’s findings were published last week in the journal Monthly Notices of the Royal Astronomical Society.
Astronomers studied the event before the debris and dust obstructed details. The team researched the gas in the accretion disk, a rotating ring of matter that emits x-rays and visible light to help show where the black hole is, to see the gas’s movement.
Data from this star-shredding event—in which a black hole one million times more massive than the star blew it away—suggests that about half the star’s material was blown up to 6,200 miles per second away from the black hole. The spherical cloud of gas blocked out much of the high-energy emissions produced as the black hole gobbled up the remainder of the star.
“This observation rules out a class of solutions that have been proposed theoretically and gives us a stronger constraint on what happens to gas around a black hole,” Kishore Patra, a UC Berkeley graduate student and lead author of the study, says in the release. “People have been seeing other evidence of wind coming out of these events, and I think this polarization study definitely makes that evidence stronger, in the sense that you wouldn’t get a spherical geometry without having a sufficient amount of wind. The interesting fact here is that a significant fraction of the material in the star that is spiraling inward doesn’t eventually fall into the black hole—it’s blown away from the black hole.”
Using the 10-foot Shane Telescope at Lick Observatory near San Jose, California, the astronomers studied the light polarization during the tidal disruption event. Only a 1 percent polarization (when the electrical field vibrates primarily in one direction) of the light seen 29 days after the event suggests that the event did not create an eccentric, asymmetric disk after disruption as originally thought.
“One of the craziest things a supermassive black hole can do is to shred a star by its enormous tidal forces,” Wenbin Lu, an assistant professor of astronomy at UC Berkeley who was involved in the work, says in the release. “These stellar tidal disruption events are one of very few ways astronomers know the existence of supermassive black holes at the centers of galaxies and measure their properties.”
Using the calculated polarized light data, researchers were able to determine the surface of the spherical cloud and observe its optical glow.
“These disruption events are so far away that you can’t really resolve them, so you can’t study the geometry of the event or the structure of these explosions,” Filippenko says. “But studying polarized light actually helps us to deduce some information about the distribution of the matter in that explosion or, in this case, how the gas—and possibly the accretion disk—around this black hole is shaped.”