BLACK-HOLE DISK ACCRETION IN SUPERNOVAE

Massive stars in a certain mass range may form low-mass black holes af ter supernova explosions. In such massive stars, fallback of similar t o 0.1 M. materials onto a black hole is expected because of a deep gra vitational potential or a reverse shock propagating back from the oute r composition interface. We study hydrodynamical disk accretion onto a newborn low-mass black hole in a supernova using the smoothed particl e hydrodynamics method. If the progenitor was rotating before the expl osion, the fallback material should have a certain amount of angular m omentum with respect to the black hole, thus forming an accretion disk . The disk material will eventually accrete toward the central object because of viscosity at a supercritical accretion rate, (M) over dot/( M) over dot(crit) > 10(6), for the first several tens of days. (Here, (M) over dot(crit) is the Eddington luminosity divided by c(2).) We th en expect that such an accretion disk is optically thick and advection dominated; that is, the disk is so hot that the produced energy and p hotons are advected inward rather than being radiated away, Thus, the disk luminosity is much less than the Eddington luminosity. The disk b ecomes hot and dense; for (M) over dot/(M) over dot(crit) similar to 1 0(6), for example, T similar to 10(9)(alpha(vis)/0.01)(-1/4) K and rho similar to 10(3)(alpha(vis)/0.01)(-1) g cm(-3) (with alpha(vis) being the viscosity parameter) in the vicinity of the black hole. Depending on the material mixing, some interesting nucleosynthesis processes vi a rapid proton and alpha-particle captures are expected even for reaso nable viscosity magnitudes (alpha(vis) similar to 0.01), and some of t hem could be ejected in a disk wind or a jet without being swallowed b y the black hole.