"Natal Kicks to Black-Hole Remnants of Magnetized Collapsars"

Abstract:

Asymmetric stellar explosions impart an impulse, or natal kick, to their compact remnants by linear momentum conservation. Neutron star natal kicks have been extensively constrained by observation, e.g., using pulsar proper motions, and many authors have investigated their origins numerically via (magneto)hydrodynamic core-collapse supernova simulations. Black hole (BH) kicks are harder to measure due to isolated BHs' electromagnetic invisibility, and previous numerical studies have omitted rapid progenitor rotation, magnetic fields, and/or general relativity. Using extremely long duration 3D general-relativistic magnetohydrodynamic simulations, we show that BHs formed from the collapse of rapidly spinning massive progenitor stars (collapsars) with strong magnetic fields can acquire strong natal kicks of hundreds of km/s due to asymmetric electromagnetic jets, magnetic flux eruptions, and the gravitational pull of aspherical ejecta. Our model suite explores the sensitivity of these mechanisms to the progenitor star structure, initial magnetic flux, and BH spin. Our results have implications for BH retention in dense stellar environments, the demographics of black hole mergers formed through isolated binary evolution, and the viability of massive “direct-horizon” collapsars as origins of highly spinning BHs within the pair-instability mass gap.