Intermediate-mass black holes are the rarest type of these extreme objects. Much heavier than a star, but not as massive as those at the center of galaxies, these black holes have only been identified a handful of times. Now, a new candidate intermediate-mass black hole has been found thanks to its gruesome actions: the ripping apart of a star in a distant dwarf galaxy.
The team had reason to believe that the transient event AT 2020neh was the destruction of a star by a black hole. Modeling of the event estimated that the black hole was between 50,000 and 800,000 times the mass of the Sun. Just for comparison, black holes found with gravitational waves are often in the tens of times the mass of the Sun. The supermassive black holes at the center of galaxies can be millions, if not billions, of solar masses.
"The fact that we were able to capture this midsize black hole whilst it devoured a star offered us a remarkable opportunity to detect what otherwise would have been hidden from us," first author Charlotte Angus at the Niels Bohr Institute said in a statement.
"What is more, we can use the properties of the flare itself to better understand this elusive group of middle-weight black holes, which could account for the majority of black holes in the centers of galaxies."
Supermassive black holes already existed very early in the universe – too early for them to make sense in many theories. One possibility is that the formation of supermassive black holes comes from the mergers of many intermediate-mass black holes. But to know if that’s correct, we need to know how many of these black holes exist.
"One of the biggest open questions in astronomy is currently how supermassive black holes form," added coauthor Vivienne Baldassare, professor of physics and astronomy at Washington State University.
"If we can understand the population of intermediate-mass black holes out there – how many there are and where they are located – we can help determine if our theories of supermassive black hole formation are correct," explained coauthor Enrico Ramirez-Ruiz, professor of astronomy and astrophysics at the University of California, Santa Cruz and Niels Bohr Professor at the University of Copenhagen.
The discovery of this object was possible thanks to the Young Supernova Experiment, an approach to spot transient events, such as supernovae or this tidal disruption event, as early as possible. The quick response was key to the estimation of the black hole's mass. More of such observations could give us a better understanding of these rare black holes.
The study is published in Nature Astronomy.