摘要:

Accretion, broadly defined, is the acquisition of relatively small amounts of stuff by an object that has already acquired its identity. It is exceedingly widespread in astrophysical systems from comets to the cosmos. We provide an overview of contexts in which accretion occurs and is of importance, noting, when possible, the first discussion of the process in each context. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55911

出版商:AIP    

年代:1998

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.55890

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

This review differs very much from other reviews on the subject. Instead of giving a detailed picture of accretion that follows from microscopic properties of matter (“dirty astrophysics”) I summarize a few fundamental principles on which the theory of black hole accretion disks rests. I stress that although the detailed properties of accretion disks modelsof coursedepend very much on dirty astrophysics, the phenomenon of black hole accretion disks is very simple indeed. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55919

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A brief overview of models of jet formation from accretion disks orbiting black holes in active galactic nuclei and Galactic X-ray binary stars as well as from young stellar objects is presented. A strong case can now be made that accretion and jet formation are controlled by hydromagnetic forces. However, the observations indicate that there are various modes of accretion and have reinvigorated the study of large scale MHD, dissipation mechanisms, particle acceleration and radiation processes. Future prospects are bright. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55929

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Our understanding of the dynamical processes which control the structure and evolution of the interaction region between an accretion disk and the central star is reviewed. If the central star is unmagnetized, this interaction is in the form of a classical boundary layer. However, if the central star is strongly magnetized, it is expected that the inner disk is truncated by the stellar field, and the accretion flow follows the stellar field lines to the magnetic poles. Several outstanding questions remain regarding this picture. It is likely that numerical MHD simulations will prove essential to answering these questions. However, in order to model the MHD turbulence, angular momentum transport, and possible dynamo action associated with the dynamics of star-disk interaction, fully three-dimensional simulations spanning long dynamical times are required. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55943

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The global linear stability of a thick accretion disc with a torus shape versus the magnetic shear instability is studied through numerical simulations. The model consists of a torus disc with constant specific angular momentum embedded in a vertical, uniform, external magnetic field. The effects of density and temperature stratification are included via the anelastic approximation. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55944

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Although numerical simulations have established magnetohydrodynamic turbulence as a possible candidate for the angular momentum transport mechanism in accretion discs there is still a need for a deeper understanding of the physics of the shear-induced turbulence. There are two complementary pathways to this goal, to analyze the results of a simulation at depth or to start from a simple state, whose evolution can be understood by semi-analytical methods and ‘extrapolate’ to the turbulent state that we want to understand. We will show examples of these two approaches. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55945

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The Strong Magnetic Field model (SFM)is described in which a very powerful, highly relativistic current loop, termed a “Storage Ring”, is formed. Gravitational accretion of diamagnetic hot plasma is guided into the galactic nucleus by the distorted dipole field, whose configuration permits the successive ejection of plasma blobs, forming a strong jet. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55946

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The physics of turbulent transport in accretion disks is reviewed. The use of a formalism based on noncircular fluctuations is particularly useful, and enables one to understand the different consequences of hydrodynamical, magnetic, and self-gravitating processes. The system of governing equations separates naturally into fluctuation dynamics, which describes how the turbulence is maintained, and mean flow dynamics, which corresponds to classical, “viscous” accretion disk theory. Only MHD processes seem capable of providing a physical basis for &agr; disk theory. Nonmagnetic processes remain a viable transport option, but are likely to be wavelike, not turbulent, and have very different dissipational properties from &agr; disks. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55947

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Recent high quality broad-band X-ray and gamma-ray observations of Galactic black holes byASCA, Ginga, RXTE,andCGROshow that the spectra cannot be described by simple thermal Comptonization models (even including a fully relativistic treatment). Multi-component models accounting for Comptonization by thermal and non-thermal electrons, Compton reflection of X/&ggr;-rays from cold matter, and emission of the optically thick accretion disk are required. In this review, I discuss recent advances in the spectral modeling of Galactic black holes and Seyferts and the codes available for such an analysis. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55948

出版商:AIP    

年代:1998

数据来源: AIP