Letter to the Editor

VLTI/GRAVITY upper limit on near-infrared emission from the nearby 33 M_⊙ black hole Gaia BH3

¹ LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS, 92190 Meudon, France
² UNIDIA, Observatoire de Paris, Université PSL, CNRS 92190 Meudon, France
³ Universidad de Concepción, Departamento de Astronomía, Casilla 160-C, Concepción, Chile
⁴ French-Chilean Laboratory for Astronomy, IRL 3386, CNRS and U. de Chile, Casilla 36-D, Santiago, Chile
⁵ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
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 Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁹ , CS 34229, 06304 Nice Cedex 4, France

^⋆ Corresponding authors; pierre.kervella@observatoiredeparis.psl.eu; pasquale.panuzzo@observatoiredeparis.psl.eu

Received: 19 December 2024
Accepted: 6 February 2025

Abstract

Context. The recent astrometric discovery of the nearby (590 pc) massive (33 M_⊙) dormant black hole candidate Gaia BH3 offers the possibility to angularly resolve the black hole from its companion star by using optical interferometry.

Aims. Our aim is to detect emission in the near-infrared K band from the close-in environment of Gaia BH3 caused by accretion.

Methods. Gaia BH3 was observed with the GRAVITY instrument using the four 8-meter Unit Telescopes of the VLT Interferometer. We searched for the signature of emission from the black hole in the interferometric data using the CANDID, PMOIRED, and exoGravity tools.

Results. With a present separation of 18 mas, the Gaia BH3 system can be well resolved angularly by GRAVITY. We did not detect emission from the black hole at a contrast level of Δm = 6.8 mag with respect to the companion star, that is, f_BH/f_⋆ < 0.2%. This corresponds to an upper limit on the continuum flux density of f_BH < 1.9 × 10⁻¹⁶ W m⁻² μm⁻¹ in the K band. In addition, we did not detect emission from the black hole in the hydrogen Brγ line.

Conclusions. The non-detection of near-infrared emission from the black hole in Gaia BH3 indicates that its accretion of the giant star wind is presently occurring at most at a very low rate. This is consistent with the limit of f_Edd < 4.9 × 10⁻⁷ derived previously on the Eddington ratio for an advection-dominated accretion flow. Deeper observations with GRAVITY may be able to detect the black hole as the companion star approaches periastron around 2030.