How does a supernova happen?
A Supernova occurs during the last evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion. The original star, called the progenitor, either collapses to a neutron star or black hole, or it is completely destroyed.
A supernova happens when there is a change in the core, or center, of a star. As a star runs out of nuclear fuel, some of its mass flows to its core. Eventually, the core is so heavy that it cannot withstand its own gravitational force. The core collapses, & boom, the giant explosion of a supernova