Stars whose central fusion reaction processes have ceased are called red giants.
Born from dust and gas, a star exists for about 10 billion years as a main-sequence_star. During this time, nuclear reactions of hydrogen fusion to helium take place in its core. At some stage, the hydrogen reserves are exhausted and the core contracts. It becomes so hot that helium fuses to carbon.
At the same time the stellar envelope expands. The surface cools down and becomes less bright, emitting a reddish glow. The diameter of the star is now much greater than at the beginning. It has become a red giant.
The life span of a red giant is about 100 million years. It then becomes a gas cloud, which dissolves into planetary nebulae. The core, whose helium reserves are now exhausted, becomes a white dwarf.
Antares (Alpha Scorpii) is a red giant. It is the main star in the constellation of Scorpio.
