January 26, 2022

Studies have found that star clusters submerged by black holes can dissolve in space

A new study found that a cluster of thousands of stars can dissolve into a cluster of dozens of black holes within a billion years. The
researchers said that this dark fate may stem from the activities of some black holes that may be found in the star cluster, and this discovery may provide clues to the future of dozens of similar star clusters in the Milky Way.
Scientists analyzed globular clusters, which are dense collections of ancient stars. Roughly spherical, each star can contain up to millions of stars. The Milky Way has more than 150 globular star clusters arranged in an almost spherical halo around the Milky Way.
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Researchers focus on Paloma 5, which is approximately 11.5 billion a year – ancient globular star cluster, located in the halo of the Milky Way, in the constellation of Serpent, about 65,000 light years from Earth
Palomar 5 is one of the most scattered globular clusters known . Studies have shown that the average mass of a globular cluster is approximately 200,000 times the mass of the sun, and its diameter is approximately 20 light years, while the mass of Palomar 5 is approximately 10,000 times the mass of the sun, but its diameter it is about 130 light years and the density is about 3,000 times lower than average. Lead author Mark Gieles, an astrophysicist at the University of Barcelona in Spain, told Space.com.
At the same time, Palomar 5 is known for its two long contrails, composed of stars dislodged by globular clusters. These spectacular tails are more than 22,800 light-years long, more than 20 degrees in the sky, or about 40 times the apparent diameter of a full moon. Palomar 5 is one of the few star clusters known to have such a long tail, which makes it the key to understanding how those tails are formed.
Previous research has shown that Palomar 5’s tail is caused by the way the Milky Way splits globular clusters. The gravity of the galaxy on one side of Palomar 5 is stronger than on the other, tearing it apart; This is an extreme version of how the moon’s gravity causes Earth’s tides. This so-called “tidal ripping not only helps explain Paloma 5’s tail, but it also helps explain the dozens of narrow streams of stars recently discovered in the Milky Way’s halo.
“I see Palomar 5 as the Rosetta Stone, which allows us to understand the formation of the stream and understand the ancestors of the stream,” Gieles said.
Scientists believe that Palomar 5 has a lower formation density, which makes it easier for tidal tearing to tear it apart and form a tail. However, some properties of its stars suggest that it once resembled the densest globular clusters.
Now, Gieles and his colleagues believe that the density of Palomar 5 may be much greater than it is now. Its current sparse nature and long tail may be due to more than 100 black holes lurking in it. The
researchers simulated the orbit and evolution of each star in Palomar 5 until the globular cluster finally disintegrated. They changed the initial properties of the simulated cluster until they found a good match with the actual observations of the cluster and its tail.
Scientists discovered that the structure and tail of Palomar 5 may have been produced by a black hole that accounts for about 20% of the mass of a globular cluster. Specifically, they believe that Palomar 5 may currently have 124 black holes, and the average mass of each black hole is about 17.2 times the mass of the sun. Overall, Gieles said, this is three times more than currently expected for globular clusters of this mass.
In this case, Palomar 5 is like a typical globular cluster, composed of black holes with only a small part of its mass. However, the gravitational force of black holes surrounds the stars near them, causing the star clusters to expand, making it easier for the gravitational force of the Milky Way to tear the stars apart. One billion years later, they calculated that Palomar 5 may have ejected all of its stars, leaving only one black hole.
Gieles and his colleagues believe that gravitational interactions in dense globular clusters can cause them to eject most black holes. Therefore, dense globular clusters can retain most of the stars. In contrast, the researchers found that globular clusters with a lower density at first, such as Palomar 5, can eject fewer black holes and instead spew out most of their stars. Therefore, black holes can completely dominate these globular clusters and constitute 100% of their mass.
“I’m glad to finally understand why some groups are big and some are small,” Gieles said. “Many people just assume that this is the result of different formation channels, that is, nature. We proved that the difference in appearance is due to evolution, which is reproduction.”
“Because Palomar 5 has several special features that are also found in all other dense star clusters. Characteristics, we can coordinate these findings and assume that the formation of Palomar 5 may be similar to all other star clusters, Gieles added.
Researchers found that when it comes to globular clusters in the outer halo of the Milky Way, that is, those that are farther from the center of the Milky Way than the sun, “about half of the clusters seem to be comparable to Palomar 5, while the other half are denser,” Giles Say. The researchers say that the Palomar 5-like half may experience a similar dominant black hole fate.
Gieles cautioned that they could design a Palomar 5 model without black holes and low density at the time of formation, but it also matched all the details seen by astronomers. However, he stated that the probability that Palomar 5 will form in this way is only 0.5%.
“It is unlikely that the ‘No black hole’ model.

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