Hubble detects first stellar-mass black hole in Omega Centauri

Astronomers using NASA's Hubble Space Telescope have found the first stellar-mass black hole in Omega Centauri, the largest and brightest globular star cluster visible from Earth. The discovery, announced on July 13, 2026, resolves a long-standing puzzle about the cluster's "missing" black holes — objects that theories predicted should exist but had eluded detection for decades.esa+1

A Black Hole Hiding in Plain Sight

The black hole, designated oMEGACat BH-2, weighs in at 4.46 solar masses and orbits with a visible companion star once every 94 years — making it the longest-period black hole binary system ever discovered. Its companion is a main-sequence turnoff star located just 20 arcseconds from the cluster's center, deep within a dense stellar neighborhood about 18,000 light-years from Earth.arxiv+1

The discovery was made by tracking the companion star's curved path across the sky using archival Hubble data spanning more than 20 years, supplemented by newer observations from the James Webb Space Telescope that together cover a 23-year baseline. Because the system was caught near its closest orbital approach — periastron — researchers were able to tightly constrain the black hole's mass even though only a partial orbit has been observed.arxiv+1

Decades of Missing Evidence

The finding is notable because, despite strong theoretical predictions that Omega Centauri should harbor a large population of stellar-mass black holes — possibly numbering in the thousands — none had been directly confirmed until now. Deep radio and X-ray surveys, as well as radial velocity searches, had all come up empty.arxiv

The research team, led by Matthew Whitaker at the University of Utah along with collaborators at the Max Planck Institute for Astronomy, the Space Telescope Science Institute, and other institutions, noted that oMEGACat BH-2's relatively low mass was "perhaps surprising" given the cluster's low metallicity, which typically favors the formation of heavier black holes.arxiv+1

A Piece of a Larger Puzzle

The discovery adds a new dimension to an already active debate about Omega Centauri's contents. In 2024, a separate team used Hubble to identify evidence for an intermediate-mass black hole at the cluster's center with at least 8,200 solar masses, though a subsequent study argued the central mass could instead be explained by a swarm of 10,000 to 20,000 stellar-mass black holes. The new finding of an individual stellar-mass black hole in a wide binary lends support to models suggesting a substantial hidden population remains throughout the cluster.science.nasa+2

The researchers noted that existing surveys have only probed a small portion of the parameter space where such systems might be found, suggesting additional black hole binaries likely await detection in Omega Centauri.arxiv