Common-envelope Dynamics of a Stellar-mass Black Hole: General Relativistic Simulations

Understand

With the goal of providing more accurate and realistic estimates of the secular behavior of the mass accretion and drag rates in the "common-envelope" scenario encountered when a black hole or a neutron star moves in the stellar envelope of a red supergiant star, we have carried out the first general relativistic simulations of the accretion flow onto a nonrotating black hole moving supersonically in a medium with regular but different density gradients.

• The simulations reveal that the supersonic motion always rapidly reaches a stationary state and it produces a shock cone in the downstream part of the flow.
• In the absence of density gradients we recover the phenomenology already observed in the well-known Bondi--Hoyle--Lyttleton accretion problem, with super-Eddington mass accretion rate and a shock cone whose axis is stably aligned with the direction of motion.
• However, as the density gradient is made stronger, the accretion rate also increases and the shock cone is progressively and stably dragged toward the direction of motion.