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Stellar graveyards: clustering of compact objects in globular clusters NGC 3201 and NGC 6397

Vitral, Eduardo and Kremer, Kyle and Libralato, Mattia and Mamon, Gary A. and Bellini, Andrea (2022) Stellar graveyards: clustering of compact objects in globular clusters NGC 3201 and NGC 6397. Monthly Notices of the Royal Astronomical Society, 514 (1). pp. 806-825. ISSN 0035-8711. doi:10.1093/mnras/stac1337.

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We analyse Gaia EDR3 and re-calibrated HST proper motion data from the core-collapsed and non-core-collapsed globular clusters NGC 6397 and NGC 3201, respectively, with the Bayesian mass-orbit modelling code MAMPOSSt-PM. We use Bayesian evidence and realistic mock data sets constructed with Agama to select between different mass models. In both clusters, the velocities are consistent with isotropy within the extent of our data. We robustly detect a dark central mass (DCM) of roughly 1000 M_⊙ in both clusters. Our MAMPOSSt-PM fits strongly prefer an extended DCM in NGC 6397, while only presenting a mild preference for it in NGC 3201, with respective sizes of a roughly one and a few per cent of the cluster effective radius. We explore the astrophysics behind our results with the CMC Monte Carlo N-body code, whose snapshots best matching the phase space observations lead to similar values for the mass and size of the DCM. The internal kinematics are thus consistent with a population of hundreds of massive white dwarfs in NGC 6397, and roughly 100 segregated stellar-mass black holes in NGC 3201, as previously found with CMC. Such analyses confirm the accuracy of both mass-orbit modelling and Monte Carlo N-body techniques, which together provide more robust predictions on the DCM of globular clusters (core-collapsed or not). This opens possibilities to understand a vast range of interesting astrophysical phenomena in clusters, such as fast radio bursts, compact object mergers, and gravitational waves.

Item Type:Article
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URLURL TypeDescription Paper
Vitral, Eduardo0000-0002-2732-9717
Kremer, Kyle0000-0002-4086-3180
Libralato, Mattia0000-0001-9673-7397
Mamon, Gary A.0000-0001-8956-5953
Bellini, Andrea0000-0003-3858-637X
Additional Information:© 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Received: 03 February 2022. Revision received: 04 May 2022. Accepted: 04 May 2022. Published: 10 June 2022. We thank the anonymous referee for the constructive report, with many insightful comments that have helped us to improve the quality of our results and clarify some descriptions in the manuscript. We also acknowledge Eugene Vasiliev for great help with the AGAMA software, which allowed us to construct our mock data and for providing an unpublished analysis of the impact of Gaia EDR3 systematics in the velocity dispersion profile of NGC 6397. We thank Sebastian Kamann as well, for useful exchanges concerning mass segregation. Eduardo Vitral was funded by an AMX doctoral grant from École Polytechnique. Kyle Kremer is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-2001751. Support for this work was provided by a grant for HST programme 13297 provided by the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. We greatly benefited from the public software PYTHON (Van Rossum & Drake 2009) packages BALROGO (Vitral 2021), SCIPY (Jones et al. 2001), NUMPY (van der Walt, Colbert & Varoquaux 2011), and MATPLOTLIB (Hunter 2007). We also used the SPYDER Integrated Development Environment (Raybaut 2009). DATA AVAILABILITY. The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.
Funding AgencyGrant Number
École PolytechniqueUNSPECIFIED
NSF Astronomy and Astrophysics FellowshipAST-2001751
NASANAS 5-26555
Gaia Multilateral AgreementUNSPECIFIED
Subject Keywords:proper motions, stars: black holes, stars: kinematics and dynamics, stars: neutron, white dwarfs, globular clusters: individual: NGC 3201; NGC 6397
Issue or Number:1
Record Number:CaltechAUTHORS:20220802-742539000
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Official Citation:Eduardo Vitral, Kyle Kremer, Mattia Libralato, Gary A Mamon, Andrea Bellini, Stellar graveyards: clustering of compact objects in globular clusters NGC 3201 and NGC 6397, Monthly Notices of the Royal Astronomical Society, Volume 514, Issue 1, July 2022, Pages 806–825,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:116014
Deposited By: George Porter
Deposited On:02 Aug 2022 22:16
Last Modified:02 Aug 2022 22:16

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