They were able to show that Palomar 5 formed with a lower population of black holes, but then stars escaped more efficiently leaving the black holes behind. The black holes worked to make it a 'puffier' cluster in gravitational slingshot interactions with the stars inside the cluster. Just before it completely dissolves - roughly a billion years from now - the cluster will consist entirely of black holes. They have been shown to contain black holes formed from the death of massive stars in a supernova explosion. 'A big unknown in this scenario is how many black holes there are in clusters, which is difficult to work out because we cannot see black holes.

Source: Daily Mail July 06, 2021 08:48 UTC