After the Death of a Star

 A supernova is one of the most powerful explosions in the universe. It happens when a very massive star reaches the end of its life and can no longer support itself against gravity. The core collapses suddenly, causing a massive explosion that blasts the outer layers of the star into space. This explosion can briefly outshine entire galaxies and spreads heavy elements like iron and gold into space. These elements later become part of new stars, planets, and even life.

A black hole forms when the core of a very massive star collapses after a supernova. Its gravity becomes so strong that nothing—not even light—can escape it. The boundary around a black hole is called the event horizon, and anything that crosses it cannot return. Black holes can be small or extremely large, with some “supermassive” ones found at the centers of galaxies. Scientists study them by observing how they affect nearby stars and gas.

A neutron star is what remains after a supernova when the core is not massive enough to become a black hole. It is incredibly dense—so dense that a spoonful of its material would weigh billions of tons on Earth. Neutron stars are made mostly of tightly packed neutrons and can spin very fast, sometimes hundreds of times per second. Some neutron stars are called pulsars because they emit beams of radiation that sweep across space like a lighthouse.

A white dwarf is the leftover core of a small to medium-sized star like the Sun after it has shed its outer layers. It is very hot at first but has no nuclear fuel, so it slowly cools and fades over billions of years. White dwarfs are extremely dense, but not as extreme as neutron stars. Eventually, they may become cold, dark objects called black dwarfs, although none are expected to exist yet because the universe is not old enough.