Astronomers using NASA's Hubble Space Telescope and James Webb Space Telescope have discovered the first stellar-mass black hole in the massive globular star cluster Omega Centauri. The black hole, dubbed oMEGACat BH-2, has a mass of 4.46 solar masses and orbits its visible star companion once every 94 years — the longest orbital period of any known black hole binary system.
The discovery is surprising because the black hole is much less massive than expected for a metal-poor environment like Omega Centauri. Models predicted the cluster should contain about 10,000 stellar-mass black holes, but this is the first one ever detected there. The finding was made by analyzing over 20 years of Hubble archival data combined with recent Webb observations using astrometry — measuring tiny stellar movements.