Research On Global Solutions Of Slim Disks Around Black Holes

The gravitational energy released through accretion process is an important energy source for many astrophysical phenomena in the universe,especially for black holes,neutron stars and white dwarves.With the enormous advancement of astronomy observations during recently years,the accretion disk theory has developed into modern advection-dominated accretion paradigm.Slim disk is a kind of optically thick,advection dominated accretion flow,in which the disk height can be comparable with the disk radius.This thesis introduces the research done by the author in the slim disk theory during my Ph.D course.By improving some inconsistency in the treatment of vertical gravitational force in the slim disk model,we find that there exists an upper limit of accretion rates for slim disks without outflows.More over,we have calculated the global solutions of slim disks after waiving the hydrostatic equilibrium in the vertical direction and made some discussions.Some calculations and discussions about slim disks with outflows are also presented.In Chapter 1 we present introductory material on black holes and accretion disks.We discuss the basic concepts of black holes and make some brief introduction about its properties and features,classification,research history and observations.Then we introduce the basis of accretion theory and some popular accretion disk models.Some discussions have also been made about disk formation and matter supply,as well as the application of disk models to observations.Chapter 2 is mainly about the calculations of accretion disks.First we introduce the concept of Eddington luminosity and explain why we could have super-Eddington radiation.Then we introduce the famous Shakura & Sunyaev Disk model,including its structure description and calculations,and discuss its limitation in disk stability and feasible accretion rates.Upon this we introduce the traditional slim disk model and describe how to calculate its global solutions.Some discussions about the basic properties of slim disks have also been presented.In Chapter 3 we discuss the improvement to traditional slim disks in detail.First we present the proof that the traditional slim disk model has some hidden inconsistency in the treatment of vertical gravitational force,especially when dealing with high accretion rates.By correcting this inconsistency we have obtained some new results from regional analysis.To further test our results, we calculate the transonic global solutions in the improved slim disk model and show that the accretion rates of slim disks have an upper limit.Some discussions are done about this model, including the reason for the upper limit and its dependence on the disk parameters.We have also studied the situation when the matter supply surpasses this limit and propose that outflow seems unavoidable.Some further study show that the vertical hydrostatic equilibrium assumption may not hold for a thick disk,so we waive this assumption and calculate the global solutions again,and find that the main conclusion about the upper limit of accretion rates for slim disks still hold.In Chapter 4 we first present the results of disk structure simulations.Then by applying these results we make some calculations about slim disks with outflows.Chapter 5 is about the research plan in the future.