Using data from ESO’s Very Large Telescope (VLT) and other telescopes, astronomers have found evidence for an intermediate-mass black hole in IRS 13, a population of dusty stellar objects within the nuclear star cluster of our Milky Way Galaxy.
Black holes have been found over a wide range of masses, from stellar-mass objects with masses of 10-100 solar masses to those found at the centers of galaxies with masses over 100,000 solar masses.
However, only a few candidate intermediate-mass black holes exist between 100 and 100,000 solar masses.
“The IRS 13 star cluster is located 0.1 light years from the center of our Galaxy,” said Dr. Florian Peißker from the Universität zu Köln and his colleagues.
“We noticed that the stars in IRS 13 move in an unexpectedly orderly pattern.”
“They had actually expected the stars to be arranged randomly.”
“Two conclusions can be drawn from this regular pattern,” they added.
“On the one hand, IRS 13 appears to interact with Sagittarius A*, the 4-million-solar-mass black hole at the heart of our Milky Way Galaxy, which leads to the orderly motion of the stars.”
“On the other hand, there must be something inside the cluster for it to be able to maintain its observed compact shape.”
Using data from VLT, the Atacama Large Millimeter/submillimeter Array (ALMA) and NASA’s Chandra X-ray telescope, the astronomers found strong evidence for a disk-like structure in IRS 13.
“Multi-wavelength observations now suggest that the reason for the compact shape of IRS 13 could be an intermediate-mass black hole located at the centre of the star cluster,” they said.
“We were able to observe characteristic X-rays and ionized gas rotating at a speed of several 100 km/s in the disk around the suspected location of the intermediate-mass black hole.”
“Another indication of the presence of an intermediate-mass black hole is the unusually high density of the star cluster, which is higher than that of any other known density of a star cluster in our Milky Way.”
“IRS 13 appears to be an essential building block for the growth of our central black hole Sagittarius A*,” Dr. Peißker said.
“This fascinating star cluster has continued to surprise the scientific community ever since it was discovered around twenty years ago. At first it was thought to be an unusually heavy star. With the high-resolution data, however, we can now confirm the building-block composition with an intermediate-mass black hole at the center.”
The results appear in the Astrophysical Journal.
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Florian Peißker et al. 2024. The Evaporating Massive Embedded Stellar Cluster IRS 13 Close to Sgr A*. II. Kinematic Structure. ApJ 970, 74; doi: 10.3847/1538-4357/ad4098
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