Probing the Presence of a Single or Binary Black Hole in the Globular Cluster NGC 6752 with Pulsar Dynamics

The five millisecond pulsars that inhabit NGC 6752 display locations oraccelerations that are quite unusual compared to all other pulsars known inglobular clusters. In particular PSR-A, a binary pulsar, lives in the clusterhalo, while PSR-B and PSR-E, located in the core, show remarkably high negativespin derivatives. This is suggestive that some uncommon dynamical process is atplay in the cluster core that we attribute to the presence of a massiveperturber. We here investigate whether a single intermediate-mass black hole,lying on the extrapolation of the Mass versus Sigma relation observed in galaxyspheroids, or a less massive binary consisting of two black holes could playthe requested role. To this purpose we simulated binary-binary encountersinvolving PSR-A, its companion star, and the black hole(s). Various scenariosare discussed in detail. In our close 4-body encounters, a black hole-blackhole binary may attract on a long-term stable orbit a millisecond pulsar.Timing measurements on the captured satellite-pulsar, member of a hierarchicaltriplet, could unambiguously unveil the presence of a black hole(s) in the coreof a globular cluster.Comment: 13 pages, 8 figures, Accepted for publication in The Astrophysical Journa