Shock wave leaving the core blows the rest of the star to pieces Shock wave gets reinvigorated because neutrinos dump about 0.1 percent of their energy into the wave. This is still enough to blow the star apart. Shock wave travels outwards through all the remaining layers of the star. This may take a few hours. Remember, this star is an asymptotic giant, so it is very large.
Supernovas glow for months after they explode.
Gas that is blown off of the star expands and makes a huge nebula called a supernova remnant This gas contains all of the elements heavier than oxygen. This is the source of all these elements in the universe. In February 1987, a star exploded in the Larger Magellenic Cloud, a nearby galaxy Even though this was a dim supernova in another galaxy, it could be seen with the naked eye. First case in which we saw the star before the explosion. Embarrassingly, this star was blue, not red.