Accretion onto compact object through stationary shock: effects of General Relativity

A core-collapse supernova is generated by the passage of a shockwave through the envelope of a massive star. The shockwave is initially launched from the “bounce” of the neutron star formed during the collapse of the stellar core. Instead of successfully exploding the star, however, numerical investigations of core-collapse supernovae find that this shock tends to “stall” at small radii (≤10 neutron star radii), with stellar material accreting onto the central object through the stalled shock. Here we present time-steady, adiabatic solutions for the density, pressure, and velocity of the shocked fluid that accretes onto the compact object through the stalled shock, and we include the effects of general relativity in the Schwarzschild metric. Similar to previous works that were carried out in the Newtonian limit, we find that the gas “settles” interior to the stalled shock; in the relativistic regime analyzed here, the velocity asymptotically approaches zero near the Schwarzschild radius. However, the mass flux across the event horizon is finite. We suggest that this finite mass flux (at all radii, from the assumed time-steady nature of the flow) implies that these solutions more accurately describe accretion onto a black hole, and not accretion onto an object with a surface at which the mass flux would be ~ zero, such as a neutron star. Our findings have implications for fallback accretion in weak and failed supernovae.