Search for: All records

Recent studies of nearby globular clusters have discovered excess dark mass in their cores, apparently in an extended distribution, and simulations indicate that this mass is composed mostly of white dwarfs (respectively stellar-mass black holes) in clusters that are core collapsed (respectively with a flatter core). We perform mass-anisotropy modelling of the closest globular cluster, M4, with intermediate slope for the inner stellar density. We use proper motion data from Gaia Early Data Release 3 (EDR3) and from observations by the Hubble Space Telescope. We extract the mass profile employing Bayesian Jeans modelling, and check our fits with realistic mock data. Our analyses return isotropic motions in the cluster core and tangential motions (β ≈ −0.4 ± 0.1) in the outskirts. We also robustly measure a dark central mass of roughly $800\pm 300 \, \rm M_\odot$ , but it is not possible to distinguish between a point-like source, such as an intermediate-mass black hole (IMBH), and a dark population of stellar remnants of extent ${\approx} 0.016\, {\rm pc} \simeq 3300\, {\rm au}$ . However, when removing a high-velocity star from the cluster centre, the same mass excess is found, but more extended (${\sim} 0.034\, {\rm pc} \approx 7000\, {\rm au}$ ). We use Monte Carlo N-body models of M4 to interpret the second outcome, and find that our excess mass is not sufficiently extended to be confidently associated with a dark population of remnants. Finally, we discuss the feasibility of these two scenarios (i.e. IMBH versus remnants), and propose new observations that could help to better grasp the complex dynamics in M4’s core.

We exploit the astro‐photometric dataset of the multi‐epoch infrared parallel field of aHubble Space TelescopeLarge Programme aimed at studying the faintest stars of the globular cluster NGC 6752 to determine the luminosity and mass functions of the multiple stellar populations of this cluster. Thanks to the measurement of proper motions and deeper completeness, the results presented in this paper represent a significant improvement over those of previous studies. We successfully derived membership probabilities reaching stars as faint as , allowing us to reliably distinguish the three main stellar populations detected within this cluster. We employed a new set of model isochrones that have been individually fit to the colour–magnitude diagram of each population. We present a comprehensive analysis of the luminosity and mass functions for three stellar populations within NGC 6752. Notably, our findings reveal differences in the present‐day luminosity and mass functions of first‐generation and second‐generation stars; these differences are consistent with the manifestation of the effects of dynamical processes acting on populations with different initial spatial distributions. Finally, we publicly release the catalogues with positions, photometry, proper motions and memberships probabilities, as well as the stacked‐image atlases and all newly calculated stellar models.