Why do different stars have different endings?

A star can end as a slowly cooling core or in an event bright enough to be seen across an enormous distance. Its story begins with gravity gathering gas into a dense region. Compression heats the gas, and if the center becomes hot enough, hydrogen nuclei fuse into helium. The energy released helps maintain pressure that resists further gravitational collapse. This is a nuclear process, not a fire that consumes oxygen.

Mass strongly influences the star's future. A more massive star has stronger inward gravity and needs a much greater rate of energy production to maintain its structure. Although it contains more material, it uses its available core hydrogen faster. More fuel therefore does not necessarily mean a longer life.

When core hydrogen becomes depleted, the star's structure changes. The core contracts and heats, while fusion can continue in surrounding layers and, under suitable conditions, begin using different nuclei. In a Sun-like star, the outer layers expand into a giant. Eventually those layers are lost, leaving a hot, dense core called a white dwarf. Without sustained fusion to replace its lost energy, that remnant gradually cools.

A massive star can proceed through additional stages of fusion. Eventually its core can lose the support needed to resist collapse. Core collapse can produce a supernova explosion and leave a neutron star or black hole. A supernova names the explosive event, not the leftover object. Mass loss, composition and a companion star affect the outcome, so the two branches are broad examples. Different stellar endings follow from how gravity, pressure and changing nuclear fuel interact.