Astronomers have finally detected the first stellar-mass black hole in the globular cluster Omega Centauri. They found it using archival data from the Hubble telescope and observations from the James Webb telescope.
Omega Centauri contains about 10 million gravitationally bound stars. Models predict it should hold roughly 10,000 stellar-mass black holes — remnants of stars that exploded. Yet for years these objects evaded detection.
This time astronomers used a different approach — astrometry (measuring very small shifts of stars over time). Sifting through more than 20 years of Hubble archive and adding fresh Webb data, the team found a star orbiting an invisible massive object. It could only be a black hole.
The object was named oMEGACat BH-2. It lies about 18,000 light-years away. Its mass is 4.46 solar masses. That is too heavy for a neutron star, so the earlier suggestion of one was ruled out. At the same time, the mass turned out lower than expected for an environment poor in heavy elements.
The visible companion star orbits the black hole once every 94 years. This is the longest orbital period among known black hole binaries.
The system was most likely formed dynamically: the star and the black hole did not begin together but found each other in the dense cluster environment. Calculations show such a pair will survive less than a billion years before encounters with nearby stars tear it apart. This matters for understanding how binary systems form and later merge to produce gravitational waves.