Hidden Black-Hole Swarm Shapes Palomar 5's Galactic Stream

Gaia data and N-body simulations indicate Palomar 5 hosts a substantial population of stellar-mass black holes—over 20% of its mass—which drove stars into its broad tidal stream; the cluster is on track to dissolve in about a billion years, leaving a black-hole–dominated remnant, suggesting globular clusters commonly harbor black holes and are key sites for future black hole mergers, with Palomar 5 acting as a Rosetta Stone for stream formation.