Timing of millisecond pulsars in NGC\,6752 -- III. On the presence of non-luminous matter in the cluster's core

TL;DR

This study uses over 20 years of pulsar timing data from five millisecond pulsars in NGC 6752 to infer the presence of non-luminous mass in the cluster's core, while ruling out a significant intermediate-mass black hole.

Contribution

It provides the first detailed pulsar timing analysis of NGC 6752's core, constraining the distribution of non-luminous matter and the absence of a large intermediate-mass black hole.

Findings

At least 2.56x10^3 solar masses of non-luminous matter in the core.

Strong evidence against an intermediate-mass black hole ≥3000 solar masses.

Pulsar accelerations reveal mass distribution in the cluster core.

Abstract

Millisecond pulsars are subject to accelerations in globular clusters (GCs) that manifest themselves in both the first and second spin period time derivatives, and can be used to explore the mass distribution of the potentials they inhabit. Here we report on over 20 yr of pulsar timing observations of five millisecond radio pulsars in the core of the core-collapse GC NGC 6752 with the Parkes (Murriyang) and MeerKAT radio telescopes, which have allowed us to measure the proper motions, positions, and first and second time derivatives of the pulsars. The pulsar timing parameters indicate that all the pulsars in the core experience accelerations and jerks that can be explained only if an amount of nonluminous mass of at least 2.56x10^3 M_SUN is present in the core of NGC 6752. On the other hand, our studies highly disfavor the presence of an intermediate-mass black hole at the center of the cluster, with a mass equal to or greater than ~3000M_SUN.