[Epoch Times, April 29, 2022](The Epoch Times reporter Di Rui compiled and reported) Astronomers call black holes with masses between 100 times and 100,000 times that of the sun as medium-sized black holes. Such black holes are rare. A new study suggests they may be located in the nuclear star clusters of some galaxies.
In the past few decades, astronomers have detected two main types of black holes, one is a small black hole with a mass less than a hundred times that of the sun, and the other is a super black hole with a mass millions of times that of the sun. Why medium-sized black holes are so rare has long been a mystery.
Scientists generally believe that medium-sized black holes exist, but there are two types of theories. “Most theories suggest that the formation of these black holes depended on the conditions of the very early universe,” said lead investigator Vivienne Baldassare, assistant professor of physics and astronomy at Washington State University. . . . we wanted to test another kind of theory—that they formed in some very dense nuclear star clusters at various times in the universe.”
Nucleus clusters, also called compact nuclei, are high-density star clusters in most galaxies, near their central regions. This type of star cluster is the densest star cluster structure known to astronomers to date.
So the team looked for traces of these black holes using observations from the Chandra X-ray Observatory. The Chandra X-ray Observatory, a space telescope orbiting the Earth, is the most powerful X-ray detector in the world today, capable of detecting very faint X-rays from distant space. The researchers focused on the nuclear clusters in 108 galaxies to look for clues about black holes.
The analysis revealed that nuclear clusters above a certain mass emit twice as much X-rays characteristic of black holes as those below this mass. In addition, the research team also found some evidence that the internal environment of this nuclear cluster is suitable for small black holes to grow into medium-sized black holes.
Therefore, the research team believes that nuclear star clusters with masses exceeding a certain value are suitable for the growth of black holes, and it is very likely that many nuclear star clusters contain medium-sized black holes. “The evidence we found means that the environment inside a sufficiently massive, dense star cluster is capable of forming black holes,” Baldassare said. This provides exciting new clues for the search for medium-sized black holes.
The study was published April 14 in The Astrophysical Journal. ◇#
Responsible editor: Ye Ziwei
