黑洞吸积理论及其天体物理学应用的近期发展(Ⅰ)

The Recent Progresses in the Theory of Black Hole Accretion and its Astrophysical Applications

黑洞吸积理论是天体物理学的一个基础理论,是认识许多高能天体系统,如活动星系核、黑洞X射线双星、伽马射线暴等的重要物理基础。该文评述了近年来黑洞吸积理论,尤其是径移主导吸积流(advection-dominated accretion flow,ADAF)模型及其变种的主要发展,并介绍该理论在银河系中心、低光度活动星系核、黑洞X射线双星等方面的应用。全文分为两篇,该文是第一篇,内容是关于黑洞的热吸积流理论及其在银河系中心的应用。

In this paper, The recent progress of the theory of black hole accretion is reviewed, focusing on the theory of advection-dominated accretion flow （ADAF） and one of its variantsluminous hot accretion flow （Yuan 2001）, and their astrophysical applications in our Galactic center-Sgr A＊, low-luminosity AGNs, and black hole X-ray binaries. The whole review consists of two papers. The present paper focuses on the theory of accretion and its application in Sgr A＊. The most important improvememnts of our understanding to ADAF is that we find outflow is important. This means that most of the accretion flow available at the outer boundary is lost in the form of outflow, rather than accreted into the horizon of the black hole. Accordingly, observations require that a large fraction of the turbulent dissipation must be used to heat electrons directly. This is another important difference to the canonical or old ADAF model in which the direct turbulent heating of electrons is assumed to be not important. Luminous hot accretion flow （LHAF） is another hot accretion flow model in addition to ADAF. The only difference of an LHAF from an ADAF is that it corresponds to higher accretion rates. ADAF only exists below a critical accretion rate, which is roughly MADAF ： α2MEdd. Here α is the viscosity parameter and MEdd ≡ 10LEdd/c^2 is defined as the Eddington accretion rate. LHAF exists between MADAF and MEdd. Below MADAF, which is the regime of an ADAF, the advection plays a cooling role. The dissipation is balanced by advection. With the increasing of M, the advection becomes smaller and smaller, and equals zero when M = MADAF. In this case the radiative cooling is balanced by the viscous dissipation. Above MADAF, which is the regime of an LHAF, advection becomes a heating role. It is the sum of viscous dissipation together with the advective heating that balances the radiative cooling. So dynamically an LHAF is similar to the spherical accretion or cooling flow in galactic clusters. The supermassive black hole in the center of our Galaxy, Sgr A＊, is unique because the angular size of the black hole is the largest in the sky thus providing detailed boundary conditions on, and much less freedom for, accretion flow models. In this paper we review advection-dominated accretion flow models for Sgr A＊, illustrating how to explain observational results including the multi-waveband spectrum, radio polarization, IR and X-ray flares, and the size measurements at radio wavebands.