Black hole pulsars and monster shocks as outcomes of black hole-neutron star mergers
Abstract
The merger of a black hole (BH) and a neutron star (NS) in most cases is expected to leave no material around the remnant BH; therefore, such events are often considered as sources of gravitational waves without electromagnetic counterparts. However, a bright counterpart can emerge if the NS is strongly magnetized, as its external magnetosphere can experience radiative shocks and magnetic reconnection during/after the merger. We use magnetohydrodynamic simulations in the dynamical spacetime of a merging BH-NS binary to investigate its magnetospheric dynamics. We find that the magnetosphere develops compressive waves that steepen into shocks. After swallowing the NS, the BH acquires a magnetosphere that quickly evolves into a split monopole configuration and then undergoes an exponential decay (balding), enabled by magnetic reconnection and also assisted by the ring-down of the remnant BH. This spinning BH drags the split monopole into rotation, forming a transient pulsar-like state. It emits a striped wind if the swallowed magnetic dipole moment is inclined to the spin axis. We predict two types of transients from this scenario: (1) a fast radio burst emitted by the shocks as they expand to large radii and (2) an X/gamma-ray burst emitted by the $e^\pm$ outflow heated by magnetic dissipation.
Acknowledgement
The authors are grateful to Ashley Bransgrove, Koushik Chatterjee, Alexander Chernoglazov, Amir Levinson, Keefe Mitman, Alexander Philippov, Eliot Quataert, Sebastiaan Selvi, Lorenzo Sironi, Anatoly Spitkovsky, Alexander Tchekhovskoy, Saul Teukolsky, Christopher Thompson, and Yici Zhong for insightful comments and discussions. YK acknowledges support by the Sherman Fairchild Foundation and by NSF Grants No. PHY-2309211, No. PHY2309231, and No. OAC-2209656 at Caltech. ERM acknowledges support by the National Science Foundation under grants No. PHY-2309210 and AST2307394, and from NASA’s ATP program under grant 80NSSC24K1229. AMB acknowledges support by NASA grants 80NSSC24K1229 and 21-ATP21-0056, and Simons Foundation grant No. 446228. BR acknowledges support by the Natural Sciences & Engineering Research Council of Canada (NSERC), the Canadian Space Agency (23JWGO2A01), and by a grant from the Simons Foundation (MP-SCMPS-00001470). BR acknowledges a guest researcher position at the Flatiron Institute, supported by the Simons Foundation. Simulations were performed on the NSF Frontera supercomputer at the Texas Advanced Computing Center under grant AST21006, and on the Delta cluster at the National Center for Supercomputing Applications (NCSA) through allocation PHY210074 from the Advanced Cyberinfrastructure Coordination Ecosystem: Services & Support (ACCESS) program, which is supported by National Science Foundation grants #2138259, #2138286, #2138307, #2137603, and
#2138296.
Software References
EinsteinToolkit (Loffler et al. 2012), Frankfurt/IllinoisGRMHD (Most et al. 2019; Etienne et al. 2015) FUKA (Papenfort et al. 2021), Kadath (Grandclement 2010), AHFinderDirect (Thornburg 2004), kuibit (Bozzola 2021), matplotlib (The Matplotlib Development Team 2024), numpy (Harris et al. 2020), scipy (Gommers et al. 2024), qnm (Stein 2019)
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Additional details
- Sherman Fairchild Foundation
- National Science Foundation
- PHY-2309211
- National Science Foundation
- PHY2309231
- National Science Foundation
- OAC-2209656
- National Science Foundation
- PHY-2309210
- National Science Foundation
- AST2307394
- National Aeronautics and Space Administration
- NASA Astrophysics Theory Program 80NSSC24K1229
- National Aeronautics and Space Administration
- 21-ATP21-0056
- Simons Foundation
- 446228
- Simons Foundation
- (MP-SCMPS-00001470
- Natural Sciences and Engineering Research Council
- Canadian Space Agency
- 23JWGO2A01
- Submitted
-
2024-12-07Submitted paper
- Caltech groups
- TAPIR, Walter Burke Institute for Theoretical Physics
- Publication Status
- Submitted