Series: Astronomy Unit Seminars
Speaker: Prof. Steven Schwartz (Imperial College)
Abstract: Microphysics is a term to describe, or hide, details at the particle or kinetic level which govern, for example, the transport of particles (diffusion), momentum (viscosity), energy (thermal conduction), and electric current (conductivity). Plasmas in astrophysical environments are rich in microphysics thanks to the multiplicity of species (electrons, various ions, and neutrals) and the often collisionless nature of the medium even over the macroscopic scales of interest. While it can be convenient to simply parameterise the physics with idealised, usually ad hoc, transport laws, at least in the case of solar system plasmas we have incredibly detailed, kinetic-scale data to guide and/or confound us. In this talk, I'll discuss some of these general ideas and apply them to the problem of collisionless shock waves, where we will see that both the multi-species and global shape of the shock influences the way energy is partitioned amongst the particle populations. Although astrophysical shocks, such as those driven by supernovae remnants, cannot be studied in the same detail, there is a growing body of data which can be used to show that they behave in a similar manner. Other microphysical processes, from magnetic reconnection to turbulence cascades and dissipation, are also open to insights from solar system observations.