Neutrino-cooled Accretion Disk and Its Stability

• Published in: The Astrophysical journal Vol. 662; no. 2; pp. 1156 - 1166
• Main Authors: Kawanaka, N, Mineshige, S
• Format: Journal Article
• Language: English
• Published: Chicago, IL IOP Publishing 20-06-2007; University of Chicago Press
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Cosmic gamma sources; Black holes; accretion, accretion disks; Gamma ray burst; Accretion disks; instabilities; black hole physics; Neutrinos; Elementary particles; Cosmology; Instability; Massless particles; gamma rays: bursts
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/517985

We investigate the structure and stability of hypercritical accretion flows around stellar-mass black holes, taking into account neutrino cooling, lepton conservation, and using for the first time a realistic equation of state in order to properly treat the dissociation of nuclei. We obtain the radial distributions of physical properties, such as density, temperature, and electron fraction, for various mass accretion rates 0.1-10 M [unk] s super(-1). We find that, depending on mass accretion rates, different physics considerably affect the structure of the disk; the most important physics are (1) the photodissociation of nuclei around r similar to 100r sub(g) for relatively low mass accretion rates (M similar to 0.01-0.1 M [unk] s super(-1)), (2) efficient neutrino cooling around r similar to 10r sub(g)-100r sub(g) for moderately high mass accretion rates (M similar to 0.2-1.0 M [unk] s super(-1)), and (3) neutrino trapping (r similar to 3r sub(g)-10r sub(g)) for very high mass accretion rates (M [unk] 2.0 M [unk] s super(-1)). We also investigate the stability of hypercritical accretion flows by drawing the thermal equilibrium curves and find that efficient neutrino cooling makes the accretion flows rather stable against both thermal and viscous modes.