New Ideas on Mechanisms of Angular Momentum Transport and Variability in Boundary Layers of Accretion Disks

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• Roman Rafikov (Princeton)
• Thursday 23 May 2013, 16:30-17:30
• Sackler Lecture Theatre, IoA (tea at 4:00 pm).

If you have a question about this talk, please contact Jay Farihi.

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.

This talk is part of the Institute of Astronomy Colloquia series.

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• Cambridge Astronomy Talks
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• Cosmology, Astrophysics and General Relativity
• Institute of Astronomy Colloquia
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• Sackler Lecture Theatre, IoA (tea at 4:00 pm)

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