Princeton University Astroplasmas Seminar

The propagation of a radiation mediated shock (RMS) in the ejecta of BNS merger is likely to affect the composition of r-process elements and, potentially, the early kilonova signal. The reason is that the merger ejecta contains a large number of r-process isotopes with different charge-to-mass ratio, which when crossing the shock experience different deceleration rates, ultimately leading to a velocity separation between the different isotopes, and their subsequent transmutations through inelastic collisions. Capture of free neutrons that cross the shock should also induce fission behind the shock. In this talk, after a brief introduction to the physics of RMS, I’ll discuss a multi-fluid model that incorporates electrostatic coupling between the different plasma constituents, as well as Coulomb and neutrino friction, in a self-consistent manner, and show that a considerable composition change via inelastic collisions of alpha particles with heavy elements downstream is expected at shock velocities >  0.25 c, if the He abundance is large enough.  If the shock is produced prior to freeze-out, neutron capture by heavy nuclei behind the shock can also lead to a significant composition change.