The precise mechanism for energy dissipation and entropy generation at such shocks is still under investigation, but it is widely accepted that the general mechanism driving these shocks consists of wave particle interaction and plasma instabilities, that operate on the scale of plasma skin depth, which is typically much shorter than the mean free path.
It is usually agreed that shocks caused by supernova remnants expanding in the interstellar medium accelerate the cosmic rays measured above the Earth's atmosphere.
Such shocks are formed by photons colliding with the electrons of the matter, and the downstream of these shocks is dominated by radiation energy density rather than thermal energy of matter.
These shocks are unique to astrophysical environments, and can be either collisionless or radiation mediated.
Relativistic shocks are theoretically expected in gamma ray bursts, active galactic nucleus jets and in some types of supernovae.