DIFFER seminar: Magnetic miracles in the accretion disks about black holes

With the recent detection of gravitational waves and the photograph' of a black hole horizon, the dynamics of these objects and their environment has moved center stage in astrophysics. The conversion of gravitational energy into electromagnetic radiation by accretion of plasma flows onto the black hole is the crucial energy source producing the picture of the horizon of the black hole. It is also the cause of the acceleration of giant plasma jets to relativistic velocities.

Time to readdress the question of why magnetized plasma accretes at all (without dissipation the accretion disk would rotate for ever at the Keplerian velocity). Since thirty years this is ascribed to anomalous dissipation caused by the turbulence of magnetohydrodynamic instabilities, in particular the Magneto-Rotational Instability (MRI). In recent research with Rony Keppens of Leuven, we throw serious doubt on this premise and replace it by a much more probable candidate: the Super-Alfvénic Rotational Instability (SARI). It has truly miraculous properties that we have not encountered before in the literature. The dynamics of magnetized plasmas never disappoints!

Prof. dr. Hans Goedbloed

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