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The puzzling dynamical status of the core of the globular cluster NGC 6752

F. R. Ferraro·A. Possenti·E. Sabbi·P. Lagani·R. T. Rood·N. D'Amico·L. Origlia
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Abstract

We have used high resolution WFPC2-HST and ground based Wide Field images to determine the center of gravity and construct an extended radial density and brightness profile of the cluster NGC 6752 including, for the first time, detailed star counts in the very inner region. The barycenter of the 9 innermost X-ray sources detected by Chandra is located only 1.9" off the new center of gravity. Both the density and the brightness profile of the central region are best fitted by a double King model, suggesting that NGC 6752 is experiencing a post-core collapse "bounce". Taking advantage from our new optical data, we discuss the puzzling nature of the accelerations displayed by the innermost millisecond pulsars detected in this cluster. We discuss two possible origins to the accelerations: 1) the overall cluster gravitational potential which would require a central projected mass to light ratio of order 6-7 and the existence of a few thousand solar masses of low-luminosity matter within the inner 0.08 pc of NGC6752; 2) the existence of a local perturber(s) of the pulsar dynamics, such as a recently proposed binary black hole of intermediate (100-$200 Msun) mass.

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F. R. Ferraro, A. Possenti, E. Sabbi, P. Lagani, R. T. Rood, N. D'Amico, L. Origlia. 2003-06-06. The puzzling dynamical status of the core of the globular cluster NGC 6752. https://doi.org/10.1086/377352

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