A Long Period Stellar-mass Black Hole Binary in ω Centauri

Whitaker, M, Kerr, E, Seth, A, Häberle, M, Strader, J, Anderson, J, Bellini, A, Clontz, C, Freeman, Z, Griggio, M, Kamann, S ORCID: 0000-0001-6604-0505, Libralato, M, Neumayer, N, González Prieto, E, Rodriguez, CL, Saracino, S, Smith, P, van de Ven, G and Wang, Z (2026) A Long Period Stellar-mass Black Hole Binary in ω Centauri. Astrophysical Journal Letters, 1006 (1). ISSN 2041-8205

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Abstract

Modern simulations of stellar dynamics in globular clusters peg a dominant role for stellar-mass black holes, but direct evidence for black holes in clusters remains limited. We present the discovery of an astrometric stellar-mass black hole–main sequence star binary in ω Centauri, the most massive Galactic globular cluster, using Hubble Space Telescope data from the oMEGACat project and additional JWST data that span a total of 23 yr. The luminous companion to the black hole is a main-sequence turnoff star, and has a period of (Formula presented) 94−42+63  yr, a semimajor axis of (Formula presented) 31−12+15  au, and an eccentricity of e = (Formula presented) 0.72−0.13+0.08. Since we observe the binary during periastron, the mass of the black hole is well constrained even though we only observe a partial orbit: the inferred black hole mass is (Formula presented) 4.46−1.01+1.22  M⊙. We call this black hole oMEGACat BH-2. This is the first astrometric discovery of a stellar-mass black hole in a globular cluster, and is the longest-period black hole binary system yet discovered. The low mass of this black hole is perhaps surprising given the low metallicity of the cluster, and shows that at least some low-mass black holes form at metallicity Z < 103<. We find that the binary is almost certainly dynamically formed and is soft, with an expected binary disruption timescale of ∼800 Myr. While the total number of black hole binaries in ω Centauri is uncertain, we show that existing surveys only cover a small area of parameter space, and that the presence of additional detectable black hole binaries is likely.

Item Type:	Article
Uncontrolled Keywords:	5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5109 Space sciences
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	American Astronomical Society
Date of acceptance:	7 June 2026
Date of first compliant Open Access:	28 August 2026
Date Deposited:	28 Aug 2026 10:30
Last Modified:	28 Aug 2026 10:30
DOI or ID number:	10.3847/2041-8213/ae7a5c
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29214

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