During the explosion, the total energy radiated by supernovae may briefly outshine the entire output of a galaxy. They emit energy equal to that of the whole lifetime of a solar-like star. The explosion blows off its stellar material away from the star, at velocities up to 30,000 km/s or 10% of the speed of light. This drives a shock wave into the surrounding interstellar medium. This sweeps up an expanding shell of gas and dust, which we see as a supernova remnant. After exploding, what is left becomes a black hole or a neutron star. 