Neutrino‐cooled Accretion Disk and Its Stability

We investigate the structure and stability of hypercritical accretion flowsaround stellar-mass black holes, taking into account neutrino cooling, leptonconservation, and firstly a realistic equation of state in order to properlytreat the dissociation of nuclei. We obtain the radial distributions ofphysical properties, such as density, temperature and electron fraction, forvarious mass accretion rates $0.1\sim 10M_{\odot}{\rm s}^{-1}$. We find that,depending on mass accretion rates, different physics affect considerably thestructure of the disk; most important physics is (1) the photodissociation ofnuclei around $r\sim 100r_g$ for relatively low mass accretion rates($\dot{M}\sim 0.01-0.1M_{\odot} {\rm s}^{-1}$), (2) efficient neutrino coolingaround $r\sim 10-100r_g$ for moderately high mass accretion rate ($\dot{M}\sim0.2-1.0M_{\odot}{\rm s}^{-1}$), and (3) neutrino trapping ($r\sim 3-10r_g$) forvery high mass accretion rate ($\dot{M}\gtrsim 2.0M_{\odot}{\rm s}^{-1}$). Wealso investigate the stability of hypercritical accretion flows by drawing thethermal equilibrium curves, and find that efficient neutrino cooling makes theaccretion flows rather stable against both thermal and viscous modes.Comment: 26 pages, 28 figures, Accepted for publication in Ap