At a certain level, the lives and deaths of stars shape everything else visible in our universe, and that everything else likes to shape the patterns of the stars. 

Stars generally form through the collapse of massive clouds of cold gas, and those stars end up forming a cluster of stars. Depending on the location of that cluster, it will get torn apart by gravity in any of a number of different ways, as some stars are pulled more or less than others. Throughout our galaxy, astronomers have found streams of stars that appear to have formed together, either as a single cluster or as a more complicated dwarf galaxy, and as that original object passes through our galaxy, it is stretched apart into a streak.

The thing about this story is it’s just that: a story told by theorists that nicely matches the data. The problem is, according to Mark Gieles: …none of the recently discovered streams have a star cluster associated with them, hence we can not be sure.

To sort if theory matches reality, a stream with an associated cluster was needed. Enter Palomar 5, a globular cluster discovered in 1950 that is extended out into the starts of a stellar stream. This system has an overabundance of black holes and not a lot of stars. Using computer models, a team led by Gieles was able to calculate that the disruption we see Palomar 5 experiencing would preferentially remove normal stars and transform the cluster from a normal distribution of stars and dense objects like black holes to the black hole dominated system we see today. To theorists: you got this!

More Information

University of Barcelona press release

“A supra-massive population of stellar-mass black holes in the globular cluster Palomar 5,” Mark Gieles et al., 2021 July 5, Nature Astronomy