2025-06-03 カリフォルニア工科大学（Caltech）
This snapshot from a simulation shows a magnetized outflow of plasma launched following the merger of a black hole and a magnetized neutron star. The light blue color maps show the strength of magnetic fields within this wind. The magnetized outflow is powered by the spin of the remnant black hole, like a rotating fan pushing air around.Credit: Yoonsoo Kim/Caltech
＜関連情報＞
- https://www.caltech.edu/about/news/star-quakes-and-monster-shock-waves
- https://iopscience.iop.org/article/10.3847/2041-8213/adbff9
- https://iopscience.iop.org/article/10.3847/2041-8213/ad785c
ブラックホール・中性子星合体の結果としてのブラックホール・パルサーとモンスター・ショック Black Hole Pulsars and Monster Shocks as Outcomes of Black Hole–Neutron Star Mergers
Yoonsoo Kim, Elias R. Most, Andrei M. Beloborodov, and Bart Ripperda
The Astrophysical Journal Letters Published: 2025 March 31
DOI:10.3847/2041-8213/adbff9
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 compressive waves excited in the magnetosphere develop into monster shocks as they propagate outward. 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 ringdown 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-ray/γ-ray burst emitted by the e± outflow heated by magnetic dissipation.
中性子星合体における非線形アルフヴェン波ダイナミクスと地殻振動からのプレマージャー放出 Nonlinear Alfvén-wave Dynamics and Premerger Emission from Crustal Oscillations in Neutron Star Mergers
Elias R. Most, Yoonsoo Kim, Katerina Chatziioannou, and Isaac Legred
The Astrophysical Journal Letters Published: 2024 September 20
DOI:10.3847/2041-8213/ad785c
Abstract
Neutron stars have solid crusts threaded by strong magnetic fields. Perturbations in the crust can excite nonradial oscillations, which can in turn launch Alfvén waves into the magnetosphere. In the case of a compact binary close to merger involving at least one neutron star, this can happen through tidal interactions causing resonant excitations that shatter the neutron star crust. We present the first numerical study that elucidates the dynamics of Alfvén waves launched in a compact binary magnetosphere. We seed a magnetic field perturbation on the neutron star crust, which we then evolve in fully general-relativistic force-free electrodynamics using a GPU-based implementation. We show that Alfvén waves steepen nonlinearly before reaching the orbital light cylinder, form flares, and dissipate energy in a transient current sheet. Our results predict radio and X-ray precursor emission from this process.
