Sometimes a star wanders too close to a supermassive black hole at the center of a galaxy and gets ripped apart, releasing an enormous burst of energy called a Tidal Disruption Event (TDE). Our previous understanding was that the star is completely destroyed, being ripped apart into a massive stream of material that produces a months-long fireworks show while the star’s remnants circle the black hole, like water flowing down a bathtub drain, before ultimately falling in. New observations from Las Cumbres Observatory reveal a Tidal Disruption Event, named AT 2022dbl, that astonished astronomers by repeating in an almost identical way about two years after the initial event. This indicates that stars may commonly survive an initial pass by a black hole, only to come back around and repeat the process before ultimately being destroyed.
Every galaxy is believed to have a supermassive black hole at the center, millions or billions of times more massive than the sun, as depicted in the movie Interstellar. When a star gets too close to the black hole, the near side gets pulled in and the far side gets flung out with enormous energy, while the material circles the black hole at near the speed of light. As it loses energy and starts to flow into the black hole, the cosmic collision of massive amounts of matter in the most extreme environment known in the universe creates an enormous burst of energy that lasts for months.
According to the theory that was initially developed in the late 1980s, astronomers thought that when a star gets close enough to be ripped apart, it would be completely destroyed. Even still, most observed Tidal Disruption Events were less energetic than predicted by the theory. While that was curious, most astronomers figured that there was so much going on in such a complex three-dimensional environment, dominated by Einstein’s General Relativity, that our simulations, which require many approximations to compute, must be lacking.
Despite dozens of observations of Tidal Disruption Events, astronomers had never convincingly seen one repeat, so before now there was never reason to believe that the star could survive and orbit the black hole for a second pass. This new result may settle the longstanding mystery of why such events have been weaker than expected from theoretical calculations. Stars aren’t destroyed in TDEs, they are only partially shredded.
The study from an international team of astronomers was published in the July edition of the Astrophysical Journal, led by Dr. Lydia Makrygianni while she was a postdoctoral researcher at Tel Aviv university. The observations were done by Las Cumbres Observatory, a global robotic network of telescopes designed to make rapid, repeat observations of phenomena that happen too quickly for conventional telescopes to capture.
The Las Cumbres Observatory team, led by Senior Scientist Dr. Andy Howell, also contributed to the study. Howell says, “Physicists have built particle accelerators on Earth, costing billions of dollars, which accelerate a single atom to near the speed of light and smash it into another one, to see the effects. At a fraction of the cost, we have built an observatory that can witness parts of a star smashing into other parts as they fall onto a black hole, at energies inconceivably above the greatest dreams of Earth-bound researchers. This is truly the frontier of physics. When you build new tools to see the universe in a new way, you will make new discoveries that upend our previous understanding.”
