Why does the initial shock wave generated by the core bounce often stall?
The infalling stellar material carries too much energy and momentum.
When the rapidly infalling outer layers of the star collide violently with the newly formed, ultra-rigid, and practically incompressible central remnant, the material cannot compress further and rebounds, generating a powerful outward-moving shock wave. Although this is the initiating mechanism for the supernova, the initial shock wave frequently loses efficacy shortly thereafter. This stalling occurs because the sheer mass and velocity (energy and momentum) of the continuing in-fall of the star's outer envelope overwhelms the propagating shock front. The infalling material effectively absorbs the energy of the shock wave, causing it to dissipate its strength rapidly before it can successfully traverse the entire star and eject its outer layers.
