Mass models of NGC 6624 without an intermediate-mass black hole

• Published in: Monthly notices of the Royal Astronomical Society 2018-02, Vol.473 (4), p.4832-4839
• Main Authors: Gieles, Mark, Balbinot, Eduardo, I. S. M. Yaaqib, Rashid, Hénault-Brunet, Vincent, Zocchi, Alice, Peuten, Miklos, Jonker, Peter G.
• Format: Article
• Language: English
• Subjects: Acceleration; Black holes; Galactic clusters; Globular clusters; Hubble Space Telescope; Kinematics; Millisecond pulsars; Space telescopes; Stellar evolution; Surface brightness
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stx2694

Abstract An intermediate-mass black hole (IMBH) was recently reported to reside in the centre of the Galactic globular cluster (GC) NGC 6624, based on timing observations of a millisecond pulsar (MSP) located near the cluster centre in projection. We present dynamical models with multiple mass components of NGC 6624 – without an IMBH – which successfully describe the surface brightness profile and proper motion kinematics from the Hubble Space Telescope (HST) and the stellar-mass function at different distances from the cluster centre. The maximum line-of-sight acceleration at the position of the MSP accommodates the inferred acceleration of the MSP, as derived from its first period derivative. With discrete realizations of the models we show that the higher-order period derivatives – which were previously used to derive the IMBH mass – are due to passing stars and stellar remnants, as previously shown analytically in literature. We conclude that there is no need for an IMBH to explain the timing observations of this MSP.