Instabilities and time evolution of hot accretion disks with electron-positron pairs

Abstract

view Abstract Citations (20) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Instabilities and Time Evolution of Hot Accretion Disks with Electron-Positron Pairs White, Timothy R. ; Lightman, Alan P. Abstract Since the 1970s, hot, optically thin, thermal accretion disks have been proposed in some models of galactic and extragalactic X-ray sources. Recent investigations of such disks, including electron-positron pairs, have found that in disks cooled by internally produced photons, there exists a critical accretion rate above which equilibrium is not possible in an annular region around r = 10GM/c^2^, where M is the mass of the central object. (The critical accretion rate corresponds to a luminosity of a few percent of the Eddington limit.) Below the critical rate, there are two self-consistent disk structures at each radius, one with a low density of pairs and one with a high density of pairs. We consider the stability and time-dependent behavior of such disks. At accretion rates below the critical value, the high pair density equilibrium is unstable to pair runaway. Such disks, when perturbed, produce pairs rampantly, then cool, and collapse toward cool, optically thick disks without pairs on a couple of hydrodynamical time scales (~ 10 hr at r = 10GM/c^2^ for M = 10^8^ M_sun_). This behavior should be accompanied by the reduction or elimination of all hard X-ray emission and an increase in UV emission. Optically thin disks subject to accretion rates above the critical rate would behave in a similar way. Because the inner regions of the optically thick disks are known to be secularly unstable, such a disk may fluctuate between optically thick and optically thin states, with an accompanying change in the spectrum. The absence of such fluctuations would suggest that the dominant X-ray and gamma-ray emission of these objects is not produced by a thermal plasma, unless the plasma is cooled by an external source of soft photons. When the spectral and luminosity fluctuations are present, their time scale provides an estimate of the mass of the central black hole. Publication: The Astrophysical Journal Pub Date: April 1990 DOI: 10.1086/168553 Bibcode: 1990ApJ...352..495W Keywords: Accretion Disks; Electron-Positron Pairs; Galactic Nuclei; Galactic Radiation; Optical Thickness; X Ray Sources; Compton Effect; Digital Simulation; Electron Energy; Elementary Particles; Astrophysics; ELEMENTARY PARTICLES; GALAXIES: NUCLEI; RADIATION MECHANISMS full text sources ADS |