This artist’s impression of black holes. Credit: ESA/Hubble, ESO, M. Kornmesser
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This discovery, the only confirmed medium-mass black hole, resides in an equally rare object known as a low-mass naked core.
Astronomers find
“We have excellent discoveries of the largest stellar-mass black hole measuring up to 100 times the size of our sun, and a supermassive black hole at the center of the galaxy that is millions of times the size of our sun, but no measurements of black color between these,” said the authors. senior Anil Seth, University of Utah professor of astronomy and co-author of the study, “This is a very big gap.” “This discovery fills a void.”
The Andromeda galaxy, or M31, is the largest galaxy in the Milky Way. Credit: NASA/JPL-Caltech
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The black hole is hidden inside B023-G078, a massive star cluster in our nearest galaxy neighbor, Andromeda. Long believed to be a globular star cluster, researchers argue that B023-G078 is not a bare core. The bare core is the remains of a small galaxy that fell into a larger galaxy and its outer star was stripped away by the force of gravity. What remains is a small, dense core orbiting the larger galaxy and at the center of that core, a black hole.
“Previously, we have found a supermassive black hole inside a massive abstract core much larger than B023-G078. We knew that there must be smaller black holes,” said lead author Rinuka Besheti of Liverpool John Moores University, who started the study while in the United States in a low-mass core, but where there was no direct evidence.
that study is Posted on January 11, 2022, in Astrophysics Journal.
The left panel shows a large-scale image of M31 with a red square and insert indicating the location and image of B023-G78 where the black hole was found. Credits: Ivan der, https://www.astroeder.com/; HST ACS / HRC
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A premonition that lingers for decades
B023-G078 is known as a massive globular star cluster – a group of globular stars that are tightly bound by gravity. However, only one observation of the object has determined its total mass, about 6.2 million solar masses. Over the years, Seth felt he was something else.
“I know object B023-G078 is one of the most massive objects in Andromeda, and I think it could be an abstract core candidate. But we need data to prove it,” said Seth. Always my advice.” discovered supermassive black holes in the bare core in 2014, the Gemini Observatory gave us the opportunity to explore the idea.”
With their new observational data from the Gemini Observatory and images from
Globular star clusters basically formed at the same time. Instead, this bare core can contain frequent ring formations, in which gas falls to the center of the galaxy, forming stars. And other star clusters can be pulled to the center by the gravitational force of the galaxy,” said Seth. “It’s kind of a desert for a lot of different things. So, stars in the bare core will be more complex than in globular clusters. And that’s what we saw on B023-G078.”
The researchers used body mass distribution to predict how fast a star should move at a given location in mass and compared it with their data. The stars with the highest speed orbit around the center. When they built a model without including a black hole, the stars in the center were very slow compared to their observations. When they add black holes, they get a speed that matches the data. Black holes add to the evidence that these objects are abstract nuclei.
“The velocity of the star that we are getting gives us direct evidence that there is some kind of dark mass right in the center,” Pechetti said. “It is very difficult for globular clusters to form large black holes. But if they are in the bare core, then there must be black holes, left over as remnants of smaller galaxies falling into larger ones.”
The researchers hope to find more bare cores that might contain medium-mass black holes. This is an opportunity to learn more about black hole populations at the center of low-mass galaxies, and to learn how galaxies are built from smaller building blocks.
“We know that large galaxies generally form from the merging of smaller galaxies, but this bare core allows us to decipher the details of earlier interactions,” said Seth.
Reference: “100,000 detected M⊙. Black Hole in M31’s Most Massive Globular Cluster: A Tidally Stripped Nucleus” oleh Renuka Pechetti, Anil Seth, Sebastian Kamann, Nelson Caldwell, Jay Strader, Mark den Brok, Nora Luetzgendorf, Nadine Neumayer, dan Karina Voggel, 11 Januari 2022, Astrophysics Journal.
DOI: 10.3847 / 1538-4357 / ac339f
Other authors include Sebastian Kaman of Liverpool John Moores University. Nelson Caldwell, Harvard-Smithsonian Center for Astrophysics; Jay Strader, Michigan State University; Mark Den Bruck, Leibniz Institute for Astrophysics, Potsdam; Nora Lutzgendorf, European Space Agency; Nadine Neumayer, Max Planck Institute of Astronomy; and Karina Vogel, Astronomical Observatory in Strasbourg.
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