Red giant star expanding

Red giant stars are late stages of stellar evolution, when the helium core contracts and the outer layers expand.

About this subject

A red giant is a star of intermediate or low mass that has exhausted the hydrogen in its core and begun helium fusion. During this phase, the core collapses under gravity while the outer layers expand enormously, reaching hundreds of times the original radius. The surface temperature drops, giving the star a reddish color. Notable examples include Aldebaran in the constellation Taurus and Arcturus in the constellation Boötes.

The expansion process occurs when radiation pressure from helium fusion pushes the outer layers outward. The star becomes unstable and may pulsate, ejecting material into space. Eventually, the red giant loses its outer layers, forming a planetary nebula, while the remaining core becomes a white dwarf. For very massive stars, the red giant phase is followed by a supernova.

About 90% of stars in the Milky Way, including the Sun, will become red giants. The Sun will reach this stage in about 5 billion years, expanding enough to engulf Mercury and Venus, and possibly Earth. The duration of the red giant phase ranges from a few hundred million years for massive stars to a few billion years for low-mass stars.

Frequently Asked Questions

What causes a red giant star to expand?

The expansion is caused by helium fusion in the core, which generates radiation pressure strong enough to push the outer layers outward while the core contracts.

What is the final fate of a red giant?

After the red giant phase, the star sheds its outer layers, forming a planetary nebula, and the core becomes a white dwarf.

Will the Sun become a red giant? When?

Yes, the Sun will become a red giant in about 5 billion years. During that phase, it will expand and may engulf the inner planets of the solar system.