One cubic meter of photon gas at the temperature 1000000000 K, enclosed in some reservoir, has the rest mass 8400 kg. Free radiation, moving in one direction, at any temperature is massless. This is not my idea. It is generally known. The supernova explodes, when a hole is burned in the shell.
Radiation acquire the direction and momentum, and, as a result, supernova losses half of it's mass.
As a result, we can register the huge gravity wave. We can also register the gamma splash, if the hole in the shell is directed at us. The remnants of supernovae also acquire the momentum and moves with high velocity in the direction opposite to the direction of gamma splash. High common residual velocities of remnants of supernovae is observable fact. This my scenario of supernova explosion completely contradicts to the general accepted ideas of collapse of supernova into black hole.