Of all the things to find hidden in your own cosmic backyard, you probably wouldn’t expect a black hole. Something of this size and impact would be pretty noticeable, you think. In this case, you would be wrong.
A study, published Monday in the journal Nature, discovered more than 100 stellar mass black holes hidden in a star cluster moving through the Milky Way.
If this finding can be validated, it will explain how the cluster came to be what it is – with its stars spaced light years apart, spreading in a stellar flux spanning 30,000 light years.
The star cluster in question is called Palomar 5, located around 80,000 light-years away.
Mark Gieles, an astrophysicist from the University of Barcelona and lead author of the study, said, “The number of black holes is roughly three times larger than expected from the number of stars in the cluster, and it means that more than 20% of the total cluster mass is made up of black holes.”
“They each have a mass of about 20 times the mass of the Sun and they formed in supernova explosions at the end of the lives of massive stars, when the cluster was still very young.”
The discovery identifies Palomar 5 as a tidal cluster, not a globular cluster. The difference is in the propagation of stars – globular clusters are made up of stars all formed around the same time, while tidal clusters have a range of ages, loosely distributed across a stream.
Since recent evidence suggests that black hole populations may exist in the central regions of globular clusters, and that gravitational interactions with black holes are known to scare stars away, scientists have included black holes in some of their simulations.