When we accurately plot the stars of our Milky Way, we can identify features that tell us about their history. This includes local details, such as the stars that have crossed the area where something is Able to find earth. They include much larger structures, such as the star trails left by smaller galaxies that have merged with ours.
But one feature we found was somewhat puzzling: the star trails were too small and thin to come from colliding galaxies. There are dozens of them that we haven’t identified the source of. The size indicates that it is from A round mass, but there is no clear mechanism for these clusters to eject stars at a rate sufficient to produce this type of flux.
Now, the research team has proposed a mechanism that’s not entirely clear: Over time, black holes can dominate the clusters that spew all stars.
demolition
A globular cluster is a dense cluster of stars orbiting the Milky Way together. They are related to each other because of mutual attraction. The complex interactions will certainly eject some stars, but not to a large enough degree, making the cluster very long-lived.
However, the researchers started their work by looking at an unusual globular cluster called Palomar 5, which has a long tail of missing stars, and has a relatively small total mass, making it somewhat diffused compared to the other clusters we studied. Lower densities make it easier for Palomar 5 to lose stars, but this could also be due to previous star loss, causing chicken and egg problems. Therefore, the researchers decided to model the evolution of globular clusters and try to find a model that could produce something similar to Palomar 5.
The researchers created a model that takes a group of stars and models their gravitational interactions with each other and the Milky Way as they orbit the galactic center. Thanks for the help from a bunch of GPUs and the right program, they were able to run these simulations for billions of years. By changing the parameters, they were able to find the factors associated with the group that ended up looking like Palomar 5.
The secret ingredient turns out to be a black hole. When black holes remain in clusters after their formation—meaning supernovae don’t transmit enough motion to send them elsewhere in the galaxy—they gradually eject nearly 90% of the cluster’s mass. This lowers the mass density by almost three times its volume, partly by ejecting stars and partly by black holes ejecting gas and other matter by heating them.
In the best-fit model for Palomar 5, the cluster is left with roughly a quarter of its black hole content, for a total of 124 of them. These black holes are also much larger than in formation (the average mass is about 17 times the mass of the Sun), suggesting that they may have fed on a large scale or underwent a merging process.
the future is black
The researchers also looked at running models that did not generate Palomar 5-like clusters to understand how black holes might influence the evolution of globular clusters. The main factor that determines whether a cluster has a rich black hole receiver is its initial density. If star clusters are dense enough, gravitational interactions tend to eject black holes before they can survive.
If the cluster had been on this path, it would have ejected more than half of its stars in a three billion year period, a rate sufficient to establish the trail of the star that started this investigation.
In low-density clusters, black holes end up near their centers, and stars are ejected instead. The researchers say that under some conditions, the cluster can evolve to the point where it is a 100% black hole, with nearly all the stars ejected.
The main drawback of this model is that it does not include interactions between stars, black holes, and gas within the cluster. The last of these factors, gases, can mediate friction that can slow down the object and prevent its ejection, but is excluded from the model.
On the plus side, this can be checked with reality. The fact that tails are mostly produced during the late phases of some clusters suggests that only a portion of the globular clusters in the Milky Way should have had them – roughly four. Tracking the movement of stars within the cluster should be able to detect the gravitational effects of black holes, allowing us to get an estimate of their number. Therefore, this idea will likely be tested before we have a GPU powerful enough to run similar simulations involving gas.
natural astronomy, 2021. DOI: 10.1038 / s41550-021-01392-2 (About DOI).
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