The most stringent upper limit set on the mass of a central black hole in 47 Tucanae using dynamical models

¹ Dipartimento di Fisica e Astronomia “Augusto Righi”, Università di Bologna, Via Piero Gobetti 93/2, 40129 Bologna, Italy
² INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, 40129 Bologna, Italy
e-mail: alessandro.dellacroce@inaf.it
³ INAF – Osservatorio astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy
⁴ Dipartimento di Fisica e Astronomia, Università di Padova, Vicolo Osservatorio 3, 35122 Padova, Italy
⁵ Physics Departement, University of Pisa, Largo Bruno Pontecorvo, 3, 56127 Pisa, Italy
⁶ INFN, Largo B. Pontecorvo 3, 56127 Pisa, Italy

Received: 26 July 2023
Accepted: 21 October 2023

Abstract

Globular clusters (GCs) have been proposed as promising sites for discovering intermediate-mass black holes (IMBHs), offering the possibility to gain crucial insights into the formation and evolution of these elusive objects. The Galactic GC 47 Tucanae (also known as NGC 104) has been suggested as a potential IMBH host, yet previous studies have yielded conflicting results. Therefore, we present a set of self-consistent dynamical models based on distribution functions (DFs) that depend on action integrals to assess the presence (or absence) of an IMBH in 47 Tucanae. Leveraging the state-of-the-art Multi Unit Spectroscopic Explorer (MUSE) and Hubble Space Telescope (HST) data, we analyzed the three-dimensional (3D) kinematics of the cluster’s central regions, fitting individual star velocities down to the sub-arcsec scale (approximately 10⁻² pc). According to our analysis, the inner kinematics of 47 Tucanae is incompatible with a central BH more massive than 578 M_⊙ (at 3σ). This is the most stringent upper limit placed thus far on the mass of a putative IMBH in 47 Tucanae via a dynamical study.