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The Puzzling Dynamical Status of the Core of the Globular Cluster NGC 6752

The Puzzling Dynamical Status of the Core of the Globular Cluster NGC 6752,10.1086/377352,Astrophysical Journal,F. R. Ferraro,A. Possenti,E. Sabbi,P.

The Puzzling Dynamical Status of the Core of the Globular Cluster NGC 6752   (Citations: 12)
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We have used high-resolution Hubble Space Telescope Wide Field Planetary Camera 2 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 nine 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 of 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 the order of 6-7 and the existence of a few thousand solar masses of low-luminosity matter within the inner 0.08 pc of NGC 6752, and (2) the existence of a local perturber(s) of the pulsar dynamics, such as a recently proposed binary black hole of intermediate (100-200Msolar) mass. Based on observations with the NASA/ESA HST, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. Also based on WFI observations collected at the European Southern Observatory, La Silla, Chile, within the observing programs 62.L-0354 and 64.L-0439.
Journal: Astrophysical Journal - ASTROPHYS J , vol. 595, no. 1, pp. 179-186, 2003
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