An Entire Swarm of Black Holes Has Been Caught Moving Through The Milky Way
A fluffy cluster of stars spilling across the sky may have a secret hidden in its heart: a swarm of over 100 stellar-mass black holes.
If this finding can be validated, it will explain how the cluster came to be the way it is - with its stars spaced light-years apart, smearing out into a stellar stream stretching across 30,000 light-years.
The star cluster in question is called Palomar 5, located around 80,000 light-years away. Such globular clusters are often considered 'fossils' of the early Universe. They're very dense and spherical, typically containing roughly 100,000 to 1 million very old stars; some, like NGC 6397, are nearly as old as the Universe itself.
In any globular cluster, all its stars formed at the same time, from the same cloud of gas. The Milky Way has around 150 known globular clusters; these objects are excellent tools for studying, for example, the history of the Universe, or the dark matter content of the galaxies they orbit.
But there's another type of star group that is gaining more attention - tidal streams, long rivers of stars that stretch across the sky. Previously, these had been difficult to identify, but with the Gaia space observatory working to map the Milky Way with high precision in three dimensions, more of these streams have been brought to light.
