A distant supermassive black hole may have bitten off more than it can chew! Not only did the star it selected for a stellar meal escape its clutches, but it came back for a second encounter!
Evidence of the death-defying star was spotted in the form of a flare that was followed by a near-identical second flare around two years later (700 days). The double-flare has been given the designation AT 2022dbl. The team behind this research ruled out the possibility that it was caused by two stars being devoured by this black hole, leaving them to conclude the flares came from two “bites” of the same stellar snack.
The discovery is the first evidence of a star escaping a destructive encounter with a supermassive black hole and then coming back to let it take a second bite. The big question is, did the star survive to return for a second rematch with the black hole?
It could therefore change our view of so-called “tidal disruption events” or “TDEs” in which black holes rip apart stars and devour their remains, indicating this could just be the first act of a longer cosmic performance.
Some black holes prefer a lighter meal
Supermassive black holes with masses equal to that of millions or billions of suns dwell at the heart of all large galaxies.
TDEs occur when unfortunate stars wander too close to these cosmic titans and experience their immense gravitational influence. This generates terrific tidal forces within the star that simultaneously squash it horizontally while stretching it vertically.
This process, vividly known as “spaghettification,” results in shredded stellar pasta, some of which falls around the black hole, wrapping around it like spaghetti around a fork, and is gradually fed to it. The rest of this material is blasted out from around the supermassive black hole.
The material that remains swirls around the black hole at incredibly speeds, generating friction that causes bursts of light, and the ejected material also flares. These flares last weeks to months, illuminating the region around the supermassive black hole, allowing it to be studied.
However, over the last decade, some TDEs have been observed that don’t behave the way scientists would expect. That is because both the temperature and brightness of some TDEs have been lower than expected. AT 2022dbl could explain this by implying that some black holes like to savour their stellar meals rather than immediately and totally destroying them.
The team now wants to know if the third time is the charm for this daring star. If it survived its second black hole encounter, the star will swoop back toward the black hole, causing a third flare around 700 days after the second.
“The question now is whether we’ll see a third flare after two more years, in early 2026,” team member and Tel Aviv University researcher Iair Arcavi said in a statement. “If we see a third flare, it means that the second one was also the partial disruption of the star.
“So maybe all such flares, which we have been trying to understand for a decade now as full stellar disruptions, are not what we thought.”
Should a third flare not erupt in two years, it would indicate that the star’s second encounter with the black hole was fatal. Should this be the case, the similarity between the first flare and the second one would imply that non-fatal and fatal TDE flares, or partial and full disruptions, look the same.
That is something that scientists had previously predicted but have never evidenced with observations.
“Either way, we’ll have to rewrite our interpretation of these flares and what they can teach us about the monsters lying in the centers of galaxies,” Arcavi concluded.
The team’s research was published on July 1 in the Astrophysical Journal Letters.
