The cosmic star clusters may “flood with black holes”, with as many as dozens of black holes per star cluster

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The cosmic star clusters may “flood with black holes”, with as many as dozens of black holes per star cluster

Scientists analyzed globular star clusters, they It is formed by dense accumulation of ancient stars. They are roughly spherical. Each globular cluster may contain as many as millions of stars. There are more than 150 globular clusters in the Milky Way, which are arranged around the Milky Way with a nearly spherical halo-like structure. in.

Researchers focused on the analysis of the “Palomar 5” star cluster, which is a globular cluster located in the halo of the Milky Way. It has been formed for about 11.5 billion years. It is about 65,000 light-years away from the Earth. Snake constellation.

The author of the research report and astrophysicist at the University of Barcelona in Spain, Mark Gilles, said that the Paloma 5 star cluster is one of the sparsest globular clusters known in the universe, and the average mass of the globular cluster is the sun. The average diameter of the Palomar 5 star cluster is about 10,000 times that of the sun, and its diameter is about 130 light-years. The overall density is 3000 times lower than the average value of globular clusters.

At the same time, the Palomar 5 star cluster is known for having two “long tails”. In fact, the long tail is made up of stars separated from the star cluster. The two spectacular long tails span 22,800 light years. The star cluster So far, one of the few long tail star clusters has been observed. This study will help scientists understand more fully how the long tail of the star cluster is formed.

Previous studies have shown that the long tail of Palomar 5 was caused by the Milky Way galaxy tearing up the star cluster. The gravitational force of the galaxy caused the overall imbalance of the traction on one side of the star cluster, which eventually caused the side of the cluster to be torn. This is an extreme version of the lunar gravity that produces ocean tides on the earth. This so-called “tidal stripping” may not only help explain the long tail structure of the Palomar 5 star cluster, it will also explain the dozens of narrow stellar streams recently discovered in the halo structure of the Milky Way.

Gilles said: “I regard the Palomar 5 star cluster as the’Rosetta Stone’, which allows us to have a deeper understanding of the formation process of the cosmic galaxy and the origin of the cosmic galaxy. ”

Scientists believe that the Palomar 5 star cluster has a low density and is easily stripped by tidal gravity, forming a tail-like structure. However, some of its stellar characteristics suggest that it may have been a denser globular cluster.

At present, Gilles and his colleagues believe that the Palomar 5 star cluster may have been dense, and the current sparseness and long tail structure may be caused by more than 100 black holes lurking inside it. .

The researchers simulated the orbit and evolution of each star in the Palomar 5 star cluster until the globular cluster finally disintegrated. They changed the initial properties of the simulated star cluster until they found that the actual observations of the cluster and the long tail structure matched it.

Scientists have discovered that the structure and long tail of Palomar 5 may be caused by a black hole that accounts for 20% of the mass of the star cluster. Specifically, they believe that the Palomar 5 star cluster may currently have 124 Each black hole is 17.2 times the mass of the sun on average. Gilles said that overall, the number of black holes in the Palomar 5 star cluster is three times the number of black holes in globular clusters of similar mass size.

In this case, like a typical globular cluster, the Palomar 5 star cluster consists of black holes that account for only a small part of its mass. However, the role of black holes cannot be underestimated. The gravitational force of black holes affects surrounding stars, causing the star cluster to expand, making it more likely to be torn apart by the Milky Way’s gravity. Their simulation calculations show that in 1 billion years, the Palomar 5 star cluster may eject all the stars, leaving only black holes.

Gilles and colleagues believe that the internal gravitational interaction of denser globular clusters may cause them to eject most of the black holes, so denser globular clusters may only retain most of their stars, and In contrast, researchers have found that globular clusters like Palomar 5 may throw fewer black holes during the initial period of lower density instead of releasing most of their stars. Therefore, black holes may completely dominate these globular clusters and occupy 100% of the mass of the cluster.

Gilles said: “What excites me the most is that I finally understand why some star clusters are large, while others are small. Many people simply think that these are different formation channels. The result is the result of the natural evolution of the universe. Our research shows that the difference in appearance is determined by evolution, which is the result of acquired evolution.”

Due to the Palomar 5 star cluster The feature of is also present in other dense clusters, so it can be speculated that the cluster may be formed in a very similar way to other clusters.

Gillles said that we can design a model of the Palomar 5 star cluster without black holes. Its density does not reach the density level when it was originally formed, but it also meets all the details observed by astronomers. However, the probability of forming star clusters in this way is only 0.5%. The “black hole-free” star cluster model is unlikely to appear in the universe, nor can it solve the problem of the Palomar 5 star cluster similar to other dense star clusters.

This discovery may help reveal the mystery of the formation of 10% globular clusters in the Milky Way. They are as fluffy as the Palomar 5 star cluster, and their mass is less than 100,000 times that of the sun, but their diameter is more than 65. Light years. Researchers believe that these fluffy globular clusters are rich in black holes and may eventually dissolve completely, producing many thin streams of stars. Future research can learn more about the inner black hole by analyzing the Palomar 5 star cluster. The latest research report is published in the July 5th issue of “Journal of Natural Astronomy”. (Ye Qingcheng)