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MHD turbulence and state changes in compact X-ray sources

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If you have a question about this talk, please contact Simon Hodgkin.

Abstract

There is evidence that the saturation levels of MHD turbulence are sensitive to the ratio of the small scale viscosity to resistivity, a quantity known as the magnetic Prandtl number Pm. This sensitivity is present when Pm ~ 1.

Interestingly, discs associated with compact X-ray sources have such a low-to-high (tracking inward) Pm transition radius on scales of tens of Schwarzschild radii. These disc sources are also known for their dramatic changes in their spectral states.

In this talk, I will show that standard alpha disc theory predicts Dwarf-Nova like outbursts when the turbulent stress is even a modestly increasing function of Pm. Implications for understanding the X-ray data will be presented, both successes of the theory and remaining challenges.

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

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