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While studying a cluster of stars in the immediate vicinity of the supermassive black hole SgrA* (Sagittarius A*) at the center of our galaxy, an international team of researchers led by PD Dr. Florian Peisker discovered signs of another, intermediate-mass Black Hole.

Despite enormous research efforts, only about ten of these intermediate-mass black holes have been discovered so far in our entire universe. Scientists believe they formed shortly after the Big Bang. By merging, they act as “seeds” for supermassive black holes. The study “The evaporating massive embedded star cluster IRS 13 near Sgr A*. II. Kinematic Structure’ was published in The Astrophysical Journal.

The analyzed star cluster IRS 13 is located 0.1 light-years from the center of our galaxy. That’s very close astronomically, but it would still require traveling from one end of our solar system to the other twenty times to cover the distance. The researchers noticed that the stars in IRS 13 move in an unexpectedly ordered pattern. They actually 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 the organized motion of the stars. On the other hand, there must be something inside the cluster for it to maintain its observed compact shape.

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

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

“This fascinating star cluster has continued to surprise the scientific community since it was discovered some twenty years ago. It was originally thought to be an unusually heavy star. With the high-resolution data, however, we can now confirm the building is a blocky 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 further insight into the processes in the star cluster.