Jeudi 04 décembre 2003
Accretion disks are ubiquitous in astrophysics, playing a central role in star formation and galactic evolution, binary stars, black holes, quasars, and possibly even gamma-ray bursts, the most explosive events in the Universe since the Big-Bang. The combination of their apparent dynamical stability (too simple), and their highly dynamical environment (too complex), rendered accretion disks, until recently, unassailable to any kind of detailed theoretical attack. Phenomenology was the only recourse.
This changed with the belated realization that sufficiently ionized, differentially rotating, laminar gases are completely disrupted by magnetic fields, breaking down into turbulent flow.
Two- and three-dimensional computer simulations of magnetohydrodynamical turbulence in accretion disks are now being pursued all over the world. In this talk, I will review the history of these developments, highlight what accretion disks have taught us more generally about fundamental fluid stability theory, and discuss some difficult astrophysical issues that numerical simulations have brought to the foreground.