Astrometric Detection of 4.46 Solar-Mass Black Hole Binary with 94-Year Period in Omega Centauri

The team combined multi-epoch HST imaging from the oMEGACat survey with JWST observations spanning 2001–2024 to measure the reflex motion of a main-sequence turnoff star. Orbital fitting of the partial arc near periastron yielded a period of 94 years, semi-major axis 31 AU, eccentricity 0.72, and a well-constrained black-hole mass of 4.46 M⊙ despite incomplete phase coverage. The binary’s softness and location in the dense core indicate dynamical formation rather than primordial pairing.

This detection directly supports N-body models showing that black holes dominate central dynamics in massive clusters and can persist in soft binaries for hundreds of Myr. The low mass at [Fe/H] < –1.5 challenges assumptions that only high-mass black holes form at low metallicity and implies that dynamical channels contribute measurably to the LIGO-Virgo-KAGRA merger rate. Existing radial-velocity and photometric surveys miss long-period systems like this one.

The principal limitation is the single-object sample and reliance on astrometric precision without radial-velocity confirmation. Expanded HST/JWST proper-motion catalogs covering the full core plus multi-epoch spectroscopy would test whether additional black-hole binaries exist and tighten the inferred retention fraction.