Emmi Meyer-Hofmeister – författare

Accretion disks in astrophysics represent the characteristic flow by which compact bodies accrete mass from their environment. Their intrinsically high luminosity, and recent progress in observational accessibility at all wavelength bands, have led to rapidly growing awareness of their importance and made them the object of intense research on widely different scales, ranging from binary stars to young stellar objects and active galactic nuclei. This book contains the proceedings of the NATO Advanced Workshop on `Theory of Accretion Disks 2' for which some of the most active researchers in the different fields came together at the Max-Planck-Institut for Astrophysics in Garching in March, 1993. Its reviews and contributions give an up-to-date account of the present status of our understanding and provide a stimulating challenge in discussions of open questions in a rapidly developing field.

In May 1986 a two-day workshop on Physical Processes in Comets, Stars and Active Galaxies was held at the Ringberg Castle near Lake Tegernsee, and this rather unusml. l collection of topics needs a few words of explanation. When we first thought of organizing a workshop on such a large variety of astrophysical objects our main motivation was to honor Rudolf Kippenhahn and Hermann Ulrich Schmidt on the occasion of their 60th birthdays, and we planned to cover at least a fraction of their fields of active research. We then realized immediately that despite the fact that the objects are so different, the physical processes involved are very much the same, and that it is this aspect of astrophysics which governed the scientific lives of both of our distinguished colleagues and friends and allowed them to make major contributions to all those fields. Apparently this viewpoint was shared by many colleagues and it was therefore not surprising that in response to our invitation everybody who had been invited agreed to come and to present a talk. The workshop then turned out to be a real success. In contrast to highly specialized conferences, fundamental problems as well as very recent devel­ opments were discussed and the participants appreciated the opportunity to exchange ideas.

In May 1986 a two-day workshop on Physical Processes in Comets, Stars and Active Galaxies was held at the Ringberg Castle near Lake Tegernsee, and this rather unusml. l collection of topics needs a few words of explanation. When we first thought of organizing a workshop on such a large variety of astrophysical objects our main motivation was to honor Rudolf Kippenhahn and Hermann Ulrich Schmidt on the occasion of their 60th birthdays, and we planned to cover at least a fraction of their fields of active research. We then realized immediately that despite the fact that the objects are so different, the physical processes involved are very much the same, and that it is this aspect of astrophysics which governed the scientific lives of both of our distinguished colleagues and friends and allowed them to make major contributions to all those fields. Apparently this viewpoint was shared by many colleagues and it was therefore not surprising that in response to our invitation everybody who had been invited agreed to come and to present a talk. The workshop then turned out to be a real success. In contrast to highly specialized conferences, fundamental problems as well as very recent devel­ opments were discussed and the participants appreciated the opportunity to exchange ideas.

The most luminous compact objects are powered by accretion of mass. Accretion disks are the one common and fundamental element of these sources on widely different scales, ranging from close stellar binaries, galactic black holes and X-ray pulsars to active galactic nuclei (AGN). Key new developments in theory and observations, reviewed by experts in the field, are presented in this book. The contributions to the workshop cover the puzzles presented by the X-UV spectra of AGN and their variability, the recent numerical simulations of magnetic fields in disks, the remarkable behavior of the superluminal source 1915+105 and the "bursting pulsar" 1744-28, to mention a few of the topics.

With the advent of space observatories and modern developments in ground­ based astronomy and concurrent progress in the theoretical understanding of these observations it has become clear that accretion of material on to compact objects is an ubiquitous mechanism powering very diverse astrophysical sources ranging in size and luminosity by many orders of magnitude. A problem common to these systems is that the material accreted must in general get rid of its angular momentum and this leads to the formation of an Accretion Disk which allows angular momentum re-distribution and converts potential energy into radiation with an efficiency which can be higher than the nuclear burning yield. These systems range in size from quasars and active galactic nuclei to accretion disks around forming stars and the early solar system and to compact binaries such as cataclysmic variables and low-mass X-ray binaries. Other objects that should be mentioned in this context are 88433, the black hole binary candidates, and possibly gamma-ray burst sources. Observations of these systems have provided important constraints for theoretical accretion disk models on widely differing scales, lumi­ nosities, mass-transfer rates and physical environments.

Accretion disks in astrophysics represent the characteristic flow by which compact bodies accrete mass from their environment. Their intrinsically high luminosity, and recent progress in observational accessibility at all wavelength bands, have led to rapidly growing awareness of their importance and made them the object of intense research on widely different scales, ranging from binary stars to young stellar objects and active galactic nuclei. This book contains the proceedings of the NATO Advanced Workshop on `Theory of Accretion Disks 2' for which some of the most active researchers in the different fields came together at the Max-Planck-Institut for Astrophysics in Garching in March, 1993. Its reviews and contributions give an up-to-date account of the present status of our understanding and provide a stimulating challenge in discussions of open questions in a rapidly developing field.

With the advent of space observatories and modern developments in ground­ based astronomy and concurrent progress in the theoretical understanding of these observations it has become clear that accretion of material on to compact objects is an ubiquitous mechanism powering very diverse astrophysical sources ranging in size and luminosity by many orders of magnitude. A problem common to these systems is that the material accreted must in general get rid of its angular momentum and this leads to the formation of an Accretion Disk which allows angular momentum re-distribution and converts potential energy into radiation with an efficiency which can be higher than the nuclear burning yield. These systems range in size from quasars and active galactic nuclei to accretion disks around forming stars and the early solar system and to compact binaries such as cataclysmic variables and low-mass X-ray binaries. Other objects that should be mentioned in this context are 88433, the black hole binary candidates, and possibly gamma-ray burst sources. Observations of these systems have provided important constraints for theoretical accretion disk models on widely differing scales, lumi­ nosities, mass-transfer rates and physical environments.