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

An intermediate-mass black hole hidden in a dwarf galaxy devoured a star that was too close to it. The shredding of the star, known as a "tidal disruption event" or TDE, produced a flare of radiation that briefly outshone the combined stellar light of the host dwarf galaxy.

The flare was captured by the Young Supernova Experiment. The discovery was reported in a paper published in Nature Astronomy.

"This discovery has created a lot of 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 mass," said Ryan Foley, an assistant professor of astronomy and astrophysics at UC Santa Cruz who helped plan the Y

The findings of the team give a baseline for future studies of black holes, according to the first author.

"The fact that we were able to capture this black hole while it devoured a star gave us a great opportunity to see what was hidden from us," he said. The properties of the flare can be used to better understand the group of middle-weight black holes, which could account for the majority of black holes in the centers of galaxies.

Our own Milky Way has a black hole at its center. Astronomers theorize that these massive beasts, with millions or billions of times the mass of the sun, could have been created from smaller black holes.

Small dwarf galaxies with intermediate-mass black holes are one of the theories for how such massive black holes were assembled. Over time, these dwarf galaxies would have merged or been taken over by more massive galaxies, their core combining each time to build up the mass in the center of the growing universe. Today's black holes are created by the merger process.

"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," said Ramirez-Ruiz.

Do all dwarfs have black holes?

It's hard to say that because detecting intermediate-mass black holes is very difficult.

Black hole hunting techniques are often not sensitive enough to find black holes in the centers of dwarf galaxies. Only a small percentage of dwarf galaxies are known to have black holes. The debate about how black holes form could be solved if more black holes are found.

One of the biggest open questions in astronomy is how super massive black holes form.

The team was able to detect the first signs of light after the black hole devoured the star. The duration of these events can be used to measure the mass of the central black hole, which is why it was important to capture this initial moment. The method was first proposed by Ramirez-Ruiz and Mockler at UC Santa Cruz.

The YSE data gave us early information about the event and we were able to pin down the mass of the black hole.

The W. M. Keck Observatory in Hawaii, the Nordic Optical Telescope, UC's Lick Observatory, NASA's Hubble Space Telescope, and the Pan-STARRS Survey at Hale were included in the study.

There is a fast-rising tidal disruption event from a candidate black hole. The article can be found at

Journal information: Nature Astronomy

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