# No evidence for intermediate-mass black holes in the globular clusters ω Cen and NGC 6624

Baumgardt, H, He, C, Sweet, SM, Drinkwater, M, Sollima, A, Hurley, J, Usher, C, Kamann, S, Dalgleish, HS, Dreizler, S and Husser, T-O (2019) No evidence for intermediate-mass black holes in the globular clusters ω Cen and NGC 6624. Monthly Notices of the Royal Astronomical Society, 488 (4). pp. 5340-5351. ISSN 0035-8711

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No evidence for intermediate-mass black holes in the globular clusters ω Cen and NGC 6624.pdf - Published Version

We compare the results of a large grid of N-body simulations with the surface brightness and velocity dispersion profiles of the globular clusters ω Cen and NGC 6624. Our models include clusters with varying stellar-mass black hole retention fractions and varying masses of a central intermediate-mass black hole (IMBH). We find that an 45,000M IMBH, whose presence has been suggested based on the measured velocity dispersion profile of $\omega$ Cen, predicts the existence of about 20 fast-moving, m>0.5 M, main-sequence stars with a (1D) velocity v>60 kms/-1 in the central 20 arcsec of ω Cen. However no such star is present in the HST/ACS proper motion catalogue of Bellini et al. (2017), strongly ruling out the presence of a massive IMBH in the core of ω Cen. Instead, we find that all available data can be fitted by a model that contains 4.6% of the mass of ω Cen in a centrally concentrated cluster of stellar-mass black holes. We show that this mass fraction in stellar-mass BHs is compatible with the predictions of stellar evolution models of massive stars. We also compare our grid of N-body simulations with NGC 6624, a cluster recently claimed to harbor a 20,000 M black hole based on timing observations of millisecond pulsars. However, we find that models with M{IMBH}>1,000 M IMBHs are incompatible with the observed velocity dispersion and surface brightness profile of NGC 6624,ruling out the presence of a massive IMBH in this cluster. Models without an IMBH provide again an excellent fit to NGC 6624.