WHAT IS A GIANT STAR?
Giant stars are stars that have expanded far beyond the size of the Sun during their evolution. The term can describe several stages and classes of evolved stars. Some of the largest examples are red supergiants, which can expand to hundreds or even more than a thousand times the Sun's radius. Their enormous size does not mean they contain a billion times more mass. A star can become much larger as its outer layers expand while its core evolves.
RED GIANTS AND SUPERGIANTS
When stars like the Sun exhaust hydrogen in their cores, their outer layers can expand dramatically and form red giants. Much more massive stars can become red supergiants. Red supergiants have enormous radii and cooler surfaces than many hot, blue stars, giving them their characteristic reddish appearance.
THE MOST MASSIVE STARS
The most massive stars can begin their lives with dozens of times the mass of the Sun. They are extremely hot, bright and powerful. Their intense radiation and stellar winds can remove enormous amounts of material from their outer layers. Because they consume their nuclear fuel so quickly, their lives are dramatically shorter than the Sun's.
THE END OF A GIANT STAR
Massive stars eventually reach a point where their cores can no longer generate enough energy to support them against gravity. The core can collapse violently, producing a supernova explosion. Depending on the mass and structure of the remaining core, the final remnant may become a neutron star or a black hole.