Hubble and Webb Find First Stellar-Mass Black Hole in Omega Centauri

Using over 20 years of Hubble archival data and recent Webb observations, astronomers have identified the first stellar-mass black hole in the globular cluster Omega Centauri, named oMEGACat BH-2.

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Astronomers have detected the first stellar-mass black hole in the globular cluster Omega Centauri, a breakthrough that addresses a long-standing mystery about the missing black hole population in such dense star systems. The discovery, made by a team led by the University of Utah, relied on more than two decades of archival data from NASA's Hubble Space Telescope combined with near-infrared observations from the James Webb Space Telescope.

The black hole, designated oMEGACat BH-2, was identified using astrometry, a technique that measures minuscule shifts in a star's position over time. The team tracked a visible main-sequence star located about 18,000 light-years away, which orbits an invisible companion. The star's motion revealed that the companion is too massive to be a neutron star, confirming it as a black hole with a mass of 4.46 solar masses.

Omega Centauri, composed of roughly 10 million stars, is expected to harbor around 10,000 stellar-mass black holes based on theoretical models. However, previous searches using radial velocity or X-ray and radio emissions had failed to find them. The new astrometric approach, applied to Hubble data spanning from 2002 to 2023 and refined with Webb's precision, finally succeeded.

The visible star, which has a mass of 0.78 solar masses, completes one orbit around the black hole every 94 years—the longest orbital period ever recorded for a black hole binary system. The system's long period suggests it formed dynamically, meaning the star and black hole encountered each other within the cluster rather than originating together. The researchers calculate that such a binary would be disrupted in less than a billion years, far shorter than the cluster's age of about 12 billion years.

"Its mass is much lower than would be expected in a metal-poor environment like Omega Centauri," said Anil Seth, a coauthor of the study. "We now know that a metal-poor star can produce a black hole like this, and we need to understand the process." The findings appeared in The Astrophysical Journal Letters on July 13, 2026.

Lead author Matthew Whitaker noted that the measurement precision was down to a fraction of a pixel on the telescopes' detectors. "It would not have been achievable without both Hubble and Webb," he said. The discovery provides new data for modeling black hole formation in globular clusters.