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Formation of Low-mass Black Holes and Single Millisecond Pulsars in Globular Clusters

Kremer, Kyle and Ye, Claire S. and Kıroğlu, Fulya and Lombardi, James C., Jr. and Ransom, Scott M. and Rasio, Frederic A. (2022) Formation of Low-mass Black Holes and Single Millisecond Pulsars in Globular Clusters. Astrophysical Journal Letters, 934 (1). Art. No. L1. ISSN 2041-8205. doi:10.3847/2041-8213/ac7ec4.

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Close encounters between neutron stars and main-sequence stars occur in globular clusters and may lead to various outcomes. Here we study encounters resulting in the tidal disruption of the star. Using N-body models, we predict the typical stellar masses in these disruptions and the dependence of the event rate on the host cluster properties. We find that tidal disruption events occur most frequently in core-collapsed globular clusters and that roughly 25% of the disrupted stars are merger products (i.e., blue straggler stars). Using hydrodynamic simulations, we model the tidal disruptions themselves (over timescales of days) to determine the mass bound to the neutron star and the properties of the accretion disks formed. In general, we find roughly 80%–90% of the initial stellar mass becomes bound to the neutron star following disruption. Additionally, we find that neutron stars receive impulsive kicks of up to about 20 km s⁻¹ as a result of the asymmetry of unbound ejecta; these kicks place these neutron stars on elongated orbits within their host cluster, with apocenter distances well outside the cluster core. Finally, we model the evolution of the (hypercritical) accretion disks on longer timescales (days to years after disruption) to estimate the accretion rate onto the neutron stars and accompanying spin-up. As long as ≳1% of the bound mass accretes onto the neutron star, millisecond spin periods can be attained. We argue the growing numbers of isolated millisecond pulsars observed in globular clusters may have formed, at least in part, through this mechanism. In the case of significant mass growth, some of these neutron stars may collapse to form low-mass (≲3 M_⊙) black holes.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Kremer, Kyle0000-0002-4086-3180
Ye, Claire S.0000-0001-9582-881X
Kıroğlu, Fulya0000-0003-4412-2176
Lombardi, James C., Jr.0000-0002-7444-7599
Ransom, Scott M.0000-0001-5799-9714
Rasio, Frederic A.0000-0002-7132-418X
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2022 April 11; revised 2022 June 7; accepted 2022 June 7; published 2022 July 18. We thank the anonymous referee for their careful review of the paper. We also thank Tony Piro, Phil Hopkins, Nick Kaaz, and Ariadna Murguia-Berthier for helpful discussions. K.K. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-2001751. F.K. acknowledges support from a CIERA Board of Visitors Graduate Fellowship. S.M.R. is a CIFAR Fellow and is supported by the NSF Physics Frontiers Center awards 1430284 and 2020265. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This work was supported by NSF grant AST-2108624 and NASA ATP grant 80NSSC22K0722 at Northwestern University.
Funding AgencyGrant Number
NSF Astronomy and Astrophysics FellowshipAST-2001751
Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA)UNSPECIFIED
Canadian Institute for Advanced Research (CIFAR)UNSPECIFIED
Subject Keywords:Globular star clusters; Hydrodynamical simulations; Neutron stars; Millisecond pulsars; Stellar mass black holes; N-body simulations
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Globular star clusters (656); Hydrodynamical simulations (767); Neutron stars (1108); Millisecond pulsars (1062); Stellar mass black holes (1611); N-body simulations (1083)
Record Number:CaltechAUTHORS:20220727-38197000
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Official Citation:Kyle Kremer et al 2022 ApJL 934 L1
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115911
Deposited By: George Porter
Deposited On:28 Jul 2022 23:10
Last Modified:28 Jul 2022 23:10

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