2026/07/24 by David F. Bambague, Cristian G. Bernal, C. G. Bernal +1
Physics and Astronomy · #Accretion (finance) #Accretion disc #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Computational astrophysics #Dynamo #Neutron #Neutron star #Pulsars and Gravitational Waves Research #Stars #astro-ph.HE
paper · pdf · doi:10.1016/j.jheap.2026.100712
published in Journal of High Energy Astrophysics 55, 100712 (Elsevier BV)
arxiv created 2026/07/24 · openalex publication_date 2026/07/24 · openalex created_date 2026/07/25 · arxiv updated 2026/08/04 · openalex updated_date 2026/08/06
Hypercritical fallback accretion can advect the surface magnetic field of a newborn neutron star into the newly accreted outer layers. Before this material joins the solid crust and enters the Hall-Ohmic regime, part of it may remain hot, dense, and liquid, allowing turbulent magnetic amplification. We investigate whether a small-scale dynamo (SSD) can operate under these conditions using six local 3D resistive MHD simulations performed with FLASH 4.7 in a periodic domain with externally forced subsonic turbulence. We explore magnetic Reynolds numbers from about 700 to 3700 and examine the effects of the equation of state, neutrino cooling, and numerical resolution. The magnetic field grows exponentially from an initial strength of 1e12 G and saturates at about (3-7)e13 G within milliseconds. The saturated magnetic energy remains below equipartition, with magnetic-to-kinetic energy ratios of about 0.2-0.3, consistent with SSD behavior for magnetic Prandtl number near unity. The reference simulations at 1283 and 2563 resolution agree within a few percent. Neutrino cooling has little effect over the simulated times, while the equation of state only weakly modifies the dynamo properties. These results indicate that a local SSD can efficiently amplify magnetic fields in the liquid post-hypercritical accretion layer and support scenarios for magnetic field reemergence in newborn neutron stars.