What is the "shockwave" of a supernova? A common notion is that supernovae create shock waves in interstellar gas, and can compress them to star forming densities.
How is that shockwave transmitted? Is it by ejected (sublight) particles, or is the radiation strong enough to move several solar masses of gas?
As one might expect,  wikipedia is our friend:

the resulting supernova explosion expels much or all of the stellar
material with velocities as much as 10% the speed of light (or
approximately 30,000 km/s). These speeds are highly supersonic, so a
strong shock wave forms ahead of the ejecta.