[ad_1]
A cluster of thousands of stars can dissolve into a host of dozens of black holes in a billion years, according to a new study.
This grim fate may result from the actions of a few black holes that may currently be in this star cluster, and the discovery could shed light on the future of dozens of similar clusters in the Milky Way, the researchers say.
Scientists analyzed globular clusters, which are dense collections of ancient stars. Roughly spherical in shape, they can each contain up to millions of stars. The Milky Way has more than 150 globular clusters arranged in an almost spherical halo around the galaxy.
Related: Scientists discover cluster of black holes at the heart of a globular cluster (video)
The researchers focused on Palomar 5, a globular cluster about 11.5 billion years old located in the Milky Way halo, about 65,000 light years from Earth in the constellation Serpens.
Palomar 5 is one of the most sparsely known globular clusters. While the average globular cluster is about 200,000 times the mass of the sun and about 20 light years in diameter, Palomar 5 is about 10,000 times the mass of the sun but about 130 light years in diameter, making it globally about 3,000 times less dense. than average, study 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 two resulting long tails, made up of stars that the globular cluster has lost. These spectacular tails stretch over 22,800 light years, or more than 20 degrees in the sky, or about 40 times the apparent diameter of the full moon. Palomar 5 is one of the few known star clusters with such long tails, which is essential for understanding how such tails might form.
Previous research suggested that Palomar 5 tails resulted from how the Milky Way tore up the globular cluster. The galaxy’s gravitational pull is stronger on one side of Palomar 5 than the other, tearing it apart – an extreme version of how the moon’s gravitational pull causes tides on Earth. This so-called “tidal stripping” may help explain not only the Palomar 5 tails, but also a few dozen narrow star streams recently detected in the Milky Way halo.
“I see Palomar 5 as a Rosetta Stone that allows us to understand the formation of streams and learn more about the ancestors of streams,” said Gieles.
Scientists had suggested that Palomar 5 formed with a low density, which allows tidal stripping to tear it apart and form its tails. However, a number of properties of its stars suggest that it was once similar to denser globular clusters.
Now, Gieles and his colleagues suggest that Palomar 5 may already have been much denser than it is today, and that its current sparse nature and long tails could be due to the more than 100 black holes lurking in it.
The researchers simulated the orbits and evolution of each star within Palomar 5 until the globular cluster eventually disintegrated. They varied the initial properties of the simulated cluster until they found good matches with the actual observations of the cluster and its tails.
Scientists have discovered that the structure and tails of Palomar 5 could come from black holes making up about 20% of the mass of the globular cluster. Specifically, they suggest that Palomar 5 may currently have 124 black holes, each averaging about 17.2 times the mass of the sun. In total, these are three times as many black holes as one would currently expect from a globular cluster of this mass, Gieles said.
In this scenario, Palomar 5, like typical globular clusters, formed with black holes making up only a small percentage of its mass. However, the gravity of the black holes wrapped around the stars as they approached them, inflating the cluster and allowing the Milky Way’s gravity to pull the stars out more easily. In a billion years, they calculated that Palomar 5 could have ejected all of its stars, leaving only black holes.
Gieles and his colleagues suggest that gravitational interactions within dense globular clusters can cause them to eject most of their black holes. As such, dense globular clusters can retain most of their stars. In contrast, the researchers found that globular clusters that start out less dense, like Palomar 5, can eject fewer black holes and instead lose most of their stars. As such, black holes can come to completely dominate these globular clusters, accounting for 100% of their mass.
“I’m very excited to finally understand why some clusters are big and others small,” said Gieles. “A lot of people have just assumed that this was the result of different channels of formation – that is, of nature. We have shown that the difference in appearance is due to evolution – that is, – say to education. ”
“Because Palomar 5 exhibits several special characteristics that are also found in all other dense clusters, we can reconcile these results and assume that Palomar 5 probably formed the same as all other clusters,” added Gieles.
The researchers found that when it comes to globular clusters in the outer halo of the Milky Way, that is, those farther from the galactic center than the sun, “about half of the clusters appear be comparable to Palomar 5 and the other half is more dense, ”said Gieles. The half that is similar to Palomar 5 could experience a similar fate dominated by black holes, the researchers said.
Gieles warned that they were able to design a model of Palomar 5 that did not have black holes and was not dense when it was formed, but also matched every detail that astronomers saw of it. Still, he said there was only a 0.5% chance that Palomar 5 would have formed this way.
“The ‘no black hole’ model is very unlikely to occur in nature and does not address the problem that Palomar 5 has properties similar to other dense clusters,” Gieles said.
These findings could help shed light on the 10% of the Milky Way’s globular clusters that are downy like Palomar 5, which are less than 100,000 times the mass of the sun but more than 65 light years in diameter. Researchers suggest that these fluffy globular clusters are rich in black holes and can eventually dissolve completely, resulting in many thin stellar fluxes.
Future research may analyze Palomar 5 to learn more about its black holes, Gieles said.
Scientists detailed their findings online July 5 in the journal Nature Astronomy.
Originally posted on Space.com.
[ad_2]
Source link