Neutrino-cooled Accretion Disks around Spinning Black Holes

We calculate the structure of accretion disks around Kerr black holes for accretion rates = 0.001-10 M_☉ s^-1. Such high- disks are plausible candidates for the central engine of gamma-ray bursts. Our disk model is fully relativistic and accurately treats the microphysics of the accreting matter: neutrino emissivity, opacity, electron degeneracy, and nuclear composition. The neutrino-cooled disk forms above a critical accretion rate _ign that depends on the black hole spin. The disk has an "ignition" radius r_ign where neutrino flux rises dramatically, cooling becomes efficient, and the proton-to-nucleon ratio Y_e drops. Other characteristic radii are r_α, where most of α-particles are disintegrated, r_ν, where the disk becomes ν-opaque, and r_tr, where neutrinos get trapped and advected into the black hole. We find r_α, r_ign, r_ν, and r_tr and show their dependence on . We discuss the qualitative picture of accretion and present sample numerical models of the disk structure. All neutrino-cooled disks regulate themselves to a characteristic state such that: (1) electrons are mildly degenerate, (2) Y_e ~ 0.1, and (3) neutrons dominate the pressure in the disk.