New Ideas on Mechanisms of Angular Momentum Transport and Variability in Boundary Layers of Accretion Disks
Roman Rafikov
Princeton University
Disk accretion onto a weakly magnetized central object, e.g. a white
dwarf or a neutron star, is inevitably accompanied by the formation of
a boundary layer near the surface, in which matter slows down from the
highly supersonic orbital velocity of the disk to the rotational velocity
of the star. Here I will describe a novel, robust mechanism of the angular
momentum transport inside the astrophysical boundary layers. Using high
resolution 2D and 3D hydrodynamical simulations in the equatorial plane
of a boundary layer we generically find that the supersonic shear in
the boundary layer excites non-axisymmetric quasi-stationary acoustic
modes that are trapped between the surface of the star and a Lindblad
resonance in the disk. These modes rotate in a prograde fashion, are
stable for hundreds of orbital periods, and have a pattern speed that
is less than and of order the rotational velocity at the inner edge
of the disk. Dissipation of acoustic modes in weak shocks provides a
universal mechanism for angular momentum and mass transport even in
purely hydrodynamic (i.e. non-magnetized) boundary layers. Periodicity
of these trapped modes may be relevant for explaining the variability
seen in accreting compact objects.
Date: | Mercredi, le 30 janvier 2013 |
Heure: | 16:00 |
Lieu: | Université McGill |
| Ernest Rutherford Physics Building, R.E. Bell Conference Room (room 103) |
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