A previously unknown black hole announced its presence to astronomers when it tore apart and devoured a star that wandered too close to it.
The intermediate-mass black hole located in a dwarf galaxy a million light-years from Earth shredded the star in an event astronomers call a tidal disturbance event (TDE). The TDE became visible when it emitted a burst of radiation so powerful that it briefly eclipsed all stars in its combined dwarf galaxy.
This TDE could help scientists better understand the relationship between galaxies and the black holes they contain. It also provides astronomers with another intermediate black hole to study. “This discovery has created widespread excitement because we can use tidal disturbance events not only to find more intermediate-mass black holes in silent dwarf galaxies, but also to measure their masses,” research co-author and UC Santa Cruz (UCSC) astronomer Ryan Foley said in a statement (opens in a new tab).
Related: Black hole ‘burps’ a ‘spaghettified’ star it devoured years ago
TDE rounding — designated At 2020neh (opens in a new tab)– was first observed by astronomers using the Young Supernova Experiment (YSE), an astronomical study that detects short-lived cosmic events like supernova explosions, when the black hole began to devour the star.
Observing this initial moment of destruction was essential for an international team led by UCSC scientists and first research author and Niels Bohr Institute astronomer Charlotte Angus to measure the mass of the black hole in finding it around between about 100,000 and 1 million times the mass of the sun. (opens in a new tab)
TDEs have been used successfully to measure the mass of supermassive black holes in the past, but this is the first time they have proven effective in documenting the masses of small, medium-sized intermediate-mass black holes.
This means that the initial observation of the incredibly fast AT 2020neh flare could provide a baseline for measuring the masses of medium-sized black holes in the future.
“The fact that we were able to capture this medium-sized black hole as it devoured a star gave us a remarkable opportunity to detect what would otherwise have been hidden from us,” Angus said. “Additionally, we can use the properties of the flare itself to better understand this elusive cluster of mid-weight black holes, which may represent the majority of black holes at the center of galaxies.”
This class of medium-sized black holes has a mass range between 100 and 100,000 times that of the sun, making them significantly more massive than stellar-mass black holes but much smaller than supermassive black holes found in at the heart of most galaxies, including the Milky Way.
Physicists have long suspected that supermassive black holes, which can have masses as large as millions or even billions of times that of the sun, could reach these enormous masses as a result of the merger of intermediate-mass black holes.
One theory regarding the mechanism that might facilitate this growth suggests that the early universe was rich in dwarf galaxies with intermediate black holes.
As these dwarf galaxies merged or were swallowed up by larger galaxies, the intermediate black holes within them cannibalized each other, increasing their mass. This chain process of larger and larger mergers would eventually lead to the supermassive black hole titans that sit at the core of most galaxies today.
“If we can understand the population of intermediate-mass black holes out there – how many there are and where they are – we can help determine if our theories about supermassive black hole formation are correct,” co-author and professor of astronomy at UCSC and astrophysics, said Enrico Ramirez-Ruiz.
One question that remains regarding this theory of black hole growth is whether all dwarf galaxies have their own intermediate-mass black hole. This question is difficult to answer because, because black holes trap light behind an outer boundary called the event horizon, they are effectively invisible unless they feed on surrounding gas and dust, or tear apart stars in the TDEs.
Astronomers can use other methods such as examining the gravitational influence of stars orbiting them to infer the presence of black holes. However, these detection methods are currently not sensitive enough to be applied to distant black holes at the center of dwarf galaxies.
As a result, few intermediate-mass black holes have been located in dwarf galaxies. This means that by detecting and measuring medium-sized black holes, TDE flares like AT 2020neh could be an essential tool in settling the debate surrounding the growth of supermassive black holes.
The team’s research was published Nov. 10 in the journal natural astronomy (opens in a new tab).
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