Structure And Stability Analyses Of Black Hole Accretion Disks

Black hole accretion is crucial process in high energy astrophysics.In this dis-sertation,we mainly discuss the physical process of black hole accretion,propose a radiative cooling-dominated accretion flow by introducing magnetic fields,study the influence of self-gravity on the structure of neutrino-dominated accretion disk,and in-vestigate the effects of the angular momentum at the outer boundary on the accretion rate.The scope of the dissertation is as follows.In section 2,we investigate the thermal stability of optically thin,two-temperature,radiative cooling-dominated accretion disks.Our linear analysis shows that the disk is thermally unstable without magnetic fields,which agrees with previous stability analy-sis on the Shapiro-Lightman-Eardley disk.By taking into account the effects of mag-netic fields,however,we find that the disk can be or partly be thermally stable.Our results may be helpful to understand the outflows in optically thin flows.Moreover,such radiative cooling-dominated disks may provide a new explanation of the differ-ent behaviors between black hole and neutron star X-ray binaries on the radio/X-ray correlation.In section 3,we present the effects of the self-gravity on the vertical structure and neutrino luminosity of the neutrino-dominated accretion disks in cylindrical coor-dinates.It is found that significant changes of the structure appear in the outer region of the disk,especially for high accretion rates(e.g.,?1M?s-1),and thus causes the slight increase of the neutrino luminosity.Furthermore,the gravitational instability of the disk is reviewed by the vertical distribution of the Toomre parameter,which may account for the late-time flares in gamma-ray bursts and the extended emission in short-duration gamma-ray bursts.In section 4,we investigate the influences of the angular momentum of the outer boundary condition on the accretion rate of an optically thin accretion flow.We find that the angular momentum plays an important role in determining the accretion rate of the solutions.The accretion rate decreases with increasing Angular momentum.By comparing our model with Bondi accretion,we find that when the density and temper-ature are the same,the accretion rate obtained by our model is significantly lower than that by the Bondi accretion model.In section 5,we divide 402392 main-sequence stars in Stripe 82 selected from the SDSS DR9 and three open clusters into 32 stellar sub-samples in narrow bins of Fe/H and g-i.We map their three-dimensional number density distribution in the Galaxy.These stellar number density maps allow an investigation of the Galactic structure with no a priori assumptions about the functional form of its components.We find that each small sample can be described by a simple exponential both vertically and radially.The scale hight changes continuously from?250 pc to?2000 pc,and the length of the sample changes continuously from?1400 pc to?6000 pc.Moreover,the large scale hight does not correspond to the large scale length,which is in great conflict with the simple thick-thin disk model.Our results may help understanding the Galactic disk formation and evolution.