Neutrino‐cooled Accretion Disks around Spinning Black Holes

We calculate the structure of accretion disks around Kerr black holes foraccretion rates 0.001 - 10 M_sun/s. Such disks are plausible candidates for thecentral engine of gamma-ray bursts. Our disk model is fully relativistic andtreats accurately microphysics of the accreting matter: neutrino emissivity,opacity, electron degeneracy, and nuclear composition. The neutrino-cooled diskforms above a critical accretion rate that depends on the black hole spin. Thedisk has the ``ignition'' radius r_ign where neutrino flux rises dramatically,cooling becomes efficient, and the proton-to-nucleon ratio Y_e drops. Othercharacteristic radii are r_alpha where most of alpha-particles aredisintegrated, r_nu where the disk becomes neutrino-opaque, and r_trap whereneutrinos get trapped and advected into the black hole. We find r_alpha, r_ign,r_nu, r_trap and show their dependence on the accretion rate. We discuss thequalitative picture of accretion and present sample numerical models of thedisk structure. All neutrino-cooled disks regulate themselves to acharacteristic state such that: (1) electrons are mildly degenerate, (2) Y_e ~0.1, and (3) neutrons dominate the pressure in the disk.Comment: 35 pages, 18 figures, accepted to Ap