Letter to the Editor

The 33 M_⊙ black hole Gaia BH3 is part of the disrupted ED-2 star cluster

¹ Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD, Groningen, The Netherlands
e-mail: eduardo.balbinot@gmail.com
² Leiden Observatory, Leiden University, Einsteinweg 55, 2333 CC, Leiden, The Netherlands
³ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
⁴ Dipartimento di Fisica e Astronomia, Universita degli Studi di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
⁵ GEPI, Observatoire de Paris, Université PSL, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
⁶ School of Physics and Astronomy, Tel Aviv University, Tel Aviv 6997801, Israel
⁷ Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290 Versoix, Switzerland
⁸ Department of Astronomy, University of Geneva, Chemin d’Ecogia 16, 1290 Versoix, Switzerland
⁹ Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles CP 226, Boulevard du Triomphe, 1050 Brussels, Belgium
¹⁰ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹¹ RHEA for European Space Agency (ESA), Camino bajo del Castillo, s/n, Urbanización Villafranca del Castillo, Villanueva de la Cañada, 28692 Madrid, Spain
¹² Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
¹³ HE Space Operations BV for European Space Agency (ESA), Camino bajo del Castillo, s/n, Urbanización Villafranca del Castillo, Villanueva de la Cañada, 28692 Madrid, Spain
¹⁴ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
¹⁵ Universidad de Granada, Departamento de Física Teórica y del Cosmos, Campus Fuente Nueva, Edificio Mecenas, 18071 Granada, Spain
¹⁶ Instituto Carlos I de Física Teórica y computacional, Universidad de Granada, 18071 Granada, Spain

Received: 17 April 2024
Accepted: 30 May 2024

Abstract

Context. The Gaia Collaboration has recently reported the detection of a 33 M_⊙ black hole in a wide binary system located in the solar neighbourhood.

Aims. Here we explore the relationship between this black hole, known as Gaia BH3, and the nearby ED-2 halo stellar stream.

Methods. We studied the orbital characteristics of the Gaia BH3 binary and present measurements of the chemical abundances of ED-2 member stars derived from high-resolution spectra obtained with the VLT.

Results. We find that the Galactic orbit of the Gaia BH3 system and its metallicity are entirely consistent with being part of the ED-2 stream. The characteristics of the stream, particularly its negligible spread in metallicity and in other chemical elements, as well as its single stellar population, suggest that it originated from a disrupted star cluster of low mass. Its age is comparable to that of the globular cluster M92 that has been estimated to be as old as the Universe.

Conclusions. This is the first black hole unambiguously associated with a disrupted star cluster. We infer the plausible mass range for the cluster to be relatively narrow, between 2 × 10³ M_⊙ and 5.2 × 10⁴ M_⊙. This implies that the black hole could have formed directly from the collapse of a massive very metal-poor star, but that the alternative scenario of binary interactions inside the cluster environment also deserves to be explored.