Answer:
black hole or neutron star
Explanation:
When a very massive star reaches its end, it runs up on its fuel. The nuclear fusion reaction in the core stops and the star goes supernova. Most of the mass and radiation is expelled out in few seconds. The event is brighter than the brightness of the entire galaxy. The remaining core after supernova collapses to form either a neutron star or a black-hole along with a nebula.
