Death of a star reveals midsize black hole lurking in a dwarf galaxy.


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Astronomers discovered a star being ripped apart by a black hole in the galaxy SDSS J152120.07+140410.5, 850 million light years away. Researchers pointed NASA’s Hubble Space Telescope to examine the aftermath, called AT 2020neh, which is shown in the center of the image. Hubble’s ultraviolet camera saw a ring of stars being formed around the nucleus of the galaxy where AT 2020neh is located. Credit: NASA, ESA, Ryan Foley/UC Santa Cruz

Astronomers learned about an undiscovered intermediate-mass black hole in a dwarf galaxy after it devoured a star that got too near. The star's destruction, referred to as a "tidal disruption event" or TDE, resulted in a flare of radiation that temporarily outshone the host dwarf galaxy's combined stellar brightness and may aid research into the interactions between black holes and galaxies.

Astronomers used the Young Supernova Experiment (YSE), a survey intended to find cosmic explosions and transient astrophysical phenomena, to record the flare. The finding was described in a publication published on November 10 in Nature Astronomy by an international team of researchers lead by researchers at UC Santa Cruz, the Niels Bohr Institute at the University of Copenhagen, and Washington State University.

According to coauthor Ryan Foley, an assistant professor of astronomy and astrophysics at UC Santa Cruz who helped plan the YSE survey, "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."

Future research on midsize black holes might use the team's results as a starting point, according to first author Charlotte Angus of the Niels Bohr Institute.

We had a great chance to see what would have otherwise been concealed from us since we were able to photograph this midsize black hole as it ate a star, according to Angus. Furthermore, we may learn more about this elusive class of middle-weight black holes—which may be responsible for the vast majority of black holes in galaxy centers—by studying the flare's physical characteristics.

All big galaxies, including the Milky Way, have supermassive black holes at their cores. These enormous monsters, with masses millions or billions of times more than that of the sun, may have developed from smaller "intermediate-mass" black holes, with masses of tens of thousands to millions of solar masses.

According to one idea, the early cosmos was filled with several tiny dwarf galaxies that contained intermediate-mass black holes. These dwarf galaxies would have merged or been swallowed up by larger galaxies throughout time, with each merger increasing the mass of the galaxy's center. The supermassive black holes we observe today were ultimately formed via this merging process.

We can determine whether our theories of supermassive black hole formation are accurate, according to coauthor Enrico Ramirez-Ruiz, professor of astronomy and astrophysics at UCSC and Niels Bohr Professor at the University of Copenhagen. "If we can understand the population of intermediate-mass black holes out there—how many there are and where they are located," he added.

Are midsize black holes present in all dwarf galaxies, though?

Ramirez-Ruiz added, "That's tough to say since locating intermediate-mass black holes is really difficult.

Black holes in the centers of dwarf galaxies are frequently invisible to traditional black hole hunting techniques, which look for actively feeding black holes. As a result, it is only known that a very small percentage of dwarf galaxies contain intermediate-mass black holes. The question of how supermassive black holes form might be resolved if more midsize black holes with tidal disruption events are discovered.

How supermassive black holes emerge is now "one of the largest outstanding mysteries in astronomy," according to co-author Vivienne Baldassare, professor of physics and astronomy at Washington State University.

The team was able to spot the first hints of light as the black hole started devouring the star thanks to information from the Young Supernova Experiment. Because the duration of these events can be used to calculate the mass of the central black hole, capturing this initial moment was crucial to understanding how big the black hole was. Ramirez-Ruiz and coauthor Brenna Mockler from UC Santa Cruz were the first to suggest this approach, which up until this point had only been shown to be effective for supermassive black holes.

Despite the fact that the flare occurred so quickly, YSE data allowed researchers to identify the black hole's mass thanks to the early information it provided.

The W. M. Keck Observatory in Hawaii, the Nordic Optical Telescope, the Lick Observatory at UC, NASA's Hubble Space Telescope, the international Gemini Observatory, the Palomar Observatory, and the Pan-STARRS Survey at Haleakala Observatory were just a few of the observatories that provided data for this study.

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