Dr Geoff Ryan

Today Geoff Ryan (NYU) defended his PhD. I wrote a few things about his work here last week and he did not disappoint in the defense. The key idea I take from his work is: In an axisymmetric system (axisymmetric matter distribution and axisymmetric force law), material will not accrete without viscosity; it will settle into an incredibly long-lived disk (like Saturn's rings!). This problem has been solved by adding viscosity (artificially, but we do expect effective sub-grid viscosity from turbulence and magnetic fields), but less has been done about non-axisymmetry. Ryan shows that in the case of a binary system (this generates the non-axisymmetry), accretion can be driven without any viscosity. That's important and deep. He also talked about numerics, and also about GRB afterglows. It was a great event and we will be sad to see him go.

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