Black hole announces itself to astronomers by tearing a star apart
A hitherto undiscovered black hole announced its presence to astronomers when it tore apart and devoured a star that wandered too close to it.
The medium black hole in a dwarf galaxy a million light-years from Soil shredded the star in an event astronomers call a Tidal Disruption Event (TDE). The TDE made itself visible when it emitted a burst of radiation so powerful it momentarily outshone every star in its dwarf galaxy combined.
This TDE could help scientists understand the relationship between galaxies and the black holes within them. It also provides astronomers with another intermediate black hole to study. “This discovery has sparked widespread excitement because we can’t just use tidal disturbances to find more medium-mass black holes in silent dwarfs. galaxies but also to measure their masses,” said study co-author and UC Santa Cruz (UCSC) astronomer Ryan Foley in a pronunciation (opens in new tab).
Related: Black hole ‘burps’ a ‘spaghettified’ star that devoured it years ago
The TDE flare — appropriate AT 2020neh (opens in new tab)— was first observed by astronomers using the Young Supernova Experiment (YSE), an astronomical study that detects short-lived cosmic events, such as supernova explosions, when the black hole first began to devour the star.
The observation of this first moment of destruction was vital to enable an international team led by UCSC scientists and first author of research and astronomer from the Niels Bohr Institute, Charlotte Angus, to determine the mass of the black hole. measure and find that it is between about 100,000 and 1 million times the mass of the sun. (opens in new tab)
TDEs have been used successfully to measure the masses of supermassive black holes in the past, but this is the first time they have been shown to work in documenting the masses of smaller medium-mass black holes.
That means the first observation of the incredibly fast AT 2020neh eruption could provide a basis for measuring medium-sized black hole masses 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 discover what would otherwise have been hidden from us,” Angus said. “In addition, we can use the properties of the flare itself to better understand this elusive group of medium-mass black holes, which could make up the majority of black holes at the centers of galaxies.”
This medium class of black holes has a mass range between 100 and 100,000 times that of the sunmaking them significantly more massive than stellar-mass black holes, but much smaller than the supermassive black holes that sit at the heart of most galaxies, including the Milky Way.
Physicists have long suspected that supermassive black holes, which can have masses millions or even billions of times that of the Sun, could grow to these massive masses as a result of the merging of medium-mass black holes.
One theory about the mechanism that could facilitate this growth suggests that the early Universe was rich in dwarf galaxies with intermediate black holes.
When these dwarf galaxies merged or were swallowed up by larger galaxies, the intermediate black holes within them cannibalize each other, causing them to grow in mass. This chain process of increasingly large mergers would eventually lead to the supermassive black hole titans that sit at the heart of most galaxies today.
“If we can understand the population of intermediate black holes — how many there are and where they are — we can help determine whether our theories about supermassive black hole formation are correct,” study co-author and UCSC professor of astronomy 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 medium-mass black hole. This is difficult to answer, because black holes trap light beyond an outer boundary called the event horizon and they are in fact invisible unless they feed on surrounding gas and dust, or if they rupture. stars in TDEs.
Astronomers can use other methods, such as looking at the gravitational pull 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 centers of dwarf galaxies.
As a result, few medium-mass black holes have been traced to dwarf galaxies. That means that by detecting and measuring medium-sized black holes, TDE outbursts such as AT 2020neh could be an essential tool in settling the debate over the growth of supermassive black holes.
The team’s research was published Nov. 10 in the journal Natural Astronomy (opens in new tab).
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