Another medium-mass black hole at the center of our galaxy

While researching a cluster of stars in the immediate vicinity of the supermassive black hole SgrA* (Sagittarius A*) in the center of our galaxy, an international team of researchers led by PD Dr. By Florian Peißker, marks of a different, medium mass. Black hole.

Despite enormous research efforts, only about ten of these intermediate-mass black holes have been found so far in our entire universe. Scientists believe that they were created shortly after the big bang. By merging, they act as “seeds” for supermassive black holes. The study “The Evaporating Massive Embedded Stellar Cluster IRS 13 Close to Sgr A*. II. Kinematic structure” is published in The Astrophysical Journal.

The analyzed star cluster IRS 13 is located 0.1 light-year from the center of our galaxy. That’s very close in astronomical terms, but it would still require traveling from one end of our solar system to the other twenty times to cover the distance. Scientists have noticed that the stars in IRS 13 move in an unexpected order. In fact, they expected the stars to be arranged randomly.

Two conclusions can be drawn from this regular pattern: On the one hand, IRS 13 appears to interact with SgrA*, leading to an orderly motion of the stars. On the other hand, there must be something inside the cluster to maintain its observed compact shape.

Multi-wavelength observations by the Very Large Telescope, as well as ALMA and Chandra, now suggest that the reason for IRS 13’s compact shape could be an intermediate-mass black hole located at the center of the cluster. This would be supported by the fact that the researchers were able to observe characteristic X-rays and ionized gas rotating at several 100 km/s in a ring around the predicted location of the intermediate-mass black hole.

Another indication of the presence of an intermediate-mass black hole is the cluster’s unusually high density, which is higher than any other known cluster density in our Milky Way.

“IRS 13 appears to be a fundamental building block for the growth of our central black hole SgrA*,” said Peißker, first author of the study.

“This fascinating star cluster has continued to surprise the scientific community since it was discovered about twenty years ago. It was initially thought to be an unusually heavy star. However, with high-resolution data, we can now confirm its building block composition with an intermediate-mass black hole at the center .”

Planned observations with the James Webb Space Telescope and the Extremely Large Telescope currently under construction will provide additional insights into the processes in the cluster.