Massive black holes (BHs) at the centers of massive galaxies are ubiquitous. However, their population in dwarf galaxies remains elusive. Identification of these systems has historically relied on detecting light emitted from accreting gaseous disks close to the black holes. Without this light, they are difficult to detect.
An international team led by scientists at UC Santa Cruz, the Niels Bohr Institute at the University of Copenhagen, and Washington State University have detected an intermediate-mass black hole lurking in a dwarf galaxy. The black hole was detected when it gobbled up an unlucky star that strayed too close.
Astronomers captured the flare using the Young Supernova Experiment (YSE), a survey designed to detect cosmic explosions and transient astrophysical events.
Tidal disruption events, the luminous flares produced when a star strays close to a black hole and is shredded, are a direct way to probe massive black holes. The rise times of these flares theoretically correlate with the black hole mass.
In this study, astronomers presented AT 2020neh, a fast-rising tidal disruption event candidate hosted by a dwarf galaxy.
Coauthor Ryan Foley, an assistant professor of astronomy and astrophysics at UC Santa Cruz, said, “This discovery has created widespread excitement because we can use tidal disruption events not only to find more intermediate-mass black holes in quiet dwarf galaxies but also to measure their masses.”
First author Charlotte Angus at the Niels Bohr Institute said the team’s findings provide a baseline for future studies of midsize black holes.
“The fact that we could capture this midsize black hole while it devoured a star offered us a remarkable opportunity to detect what otherwise would have been hidden from us. What is more, we can use the properties of the flare itself to understand better this elusive group of middle-weight black holes, which could account for the majority of black holes in the centers of galaxies.”
Coauthor Enrico Ramirez-Ruiz, professor of astronomy and astrophysics at UCSC, and Niels Bohr, Professor at the University of Copenhagen, said, “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.”
“That’s difficult to assert because detecting intermediate-mass black holes is extremely challenging.”