Medium-sized black hole observed in a dwarf galaxy when it ate a star

November 11, 2022Reviewed by Alex Smith

An intermediate-mass black hole orbiting undetected in a dwarf galaxy was exposed to astronomers when it ate an unlucky star that drifted too close.

The star’s fragmentation, called a “tidal disruption event” (TDE), created a burst of radiation that fleetingly outshone the collective starlight of the host dwarf galaxy and could help researchers gain a better picture of the relationship between galaxies and black holes.

The flare was captured by astronomers with the Young Supernova Experiment (YSE), a survey designed to detect transient astrophysical events and cosmic explosions.

An international team led by researchers at the University of California, Santa Cruz (UC Santa Cruz), Washington State University and the Niels Bohr Institute at the University of Copenhagen announced the discovery in a paper published on November 10.^u issue of the magazine Astronomy of Nature.

This discovery has generated widespread excitement because we can use tidal disruption events not only to find more intermediate-mass black holes in quiescent dwarf galaxies, but also to measure their mass.

Ryan Foley, Study Co-Author and Assistant Professor of Astronomy and Astrophysics, University of California, Santa Cruz

Ryan Foley helped design the YSE survey. Study first author Charlotte Angus at the Niels Bohr Institute said the team’s findings provide a basis for further studies of medium-sized black holes.

“The fact that we were able to capture this medium-sized black hole while it was devouring a star offered us a remarkable opportunity to detect 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 account for the majority of black holes at the centers of galaxies.

Charlotte Angus, First Study Author, Niels Bohr Institute

Supermassive black holes are found at the centers of all large galaxies, including the Milky Way. Astronomers speculate that these massive black holes, with millions or billions of times the mass of the sun, may have grown from smaller “intermediate mass” black holes with thousands to hundreds of thousands of solar masses.

One idea of ​​how such massive black holes coalesced is that the early universe was full of small dwarf galaxies that had intermediate-mass black holes.

Gradually, these dwarf galaxies would have merged with or been eaten by more giant galaxies, their nuclei merging each time to pile up the mass at the center of the growing galaxy. This fusion process will eventually form the supermassive black holes seen 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 whether our theories about the formation of supermassive black holes are correct.

Enrico Ramirez-Ruiz, Study Co-Author and Professor of Astronomy and Astrophysics, University of California, Santa Cruz

Enrico Ramirez-Ruiz is also Niels Bohr Professor at the University of Copenhagen.

The question is, do all dwarf galaxies have medium-sized black holes?

“This is difficult to confirm, because detecting intermediate-mass black holes is extremely difficult.” Ramirez-Ruiz said.

Traditional black hole hunting methods, which look for strongly powered black holes, are mostly not sensitive enough to the exposure of black holes in the centers of dwarf galaxies.

Consequently, only a small fraction of dwarf galaxies have been shown to host intermediate-mass black holes. The discovery of additional medium-sized black holes with tidal disruption events could help end the debate about how supermassive black holes grow.

“One of the biggest open questions in astronomy right now is how supermassive black holes form.” said study co-author Vivienne Baldassare, who is a professor of physics and astronomy at the University of Washington.

The data from YSE allowed researchers to observe the first signs of light as the black hole began to eat away at the star. Capturing this preliminary moment was fundamental to solving how big the black hole was, because the length of these events can be used to quantify the mass of the central black hole.

This technique, which so far has only been shown to work well for supermassive black holes, was first proposed by Ramirez-Ruiz and study co-author Brenna Mockler at UC Santa Cruz.

This flare was incredibly fast, but because the YSE data gave us so much early information about the event, we were actually able to detect the mass of the black hole using it.

Charlotte Angus, First Study Author, Niels Bohr Institute

This study was based on data from global observatories including the WM Keck Observatory in Hawaii, NASA’s Hubble Space Telescope, UC’s Lick Observatory, the Nordic Optical Telescope, the Palomar Observatory, the Gemini International Observatory, and the Pan-STARRS Survey at Haleakala Observatory .

Journal Reference:

Angus, CR, et al. (2022) A rapidly accreting tidal disturbance event from a candidate intermediate-mass black hole. Astronomy of Nature. doi.org/ 10.1038/s41550-022-01811-y.

Source: https://news.ucsc.edu