Red Giant

Key Stage 4

Red giants are too far away to get a clear image of their surface, so this is an artist's impression of a red giant.

A red giant is a star in which the Hydrogen isotopes have run out and energy is released from the fusion of Helium.

When a main sequence star runs out of Hydrogen the core collapses because there is an inward pressure of gravity but no outward pressure from fusion. Eventually the core collapses to heat the core enough that fusion of Helium can occur.

As the core of the red giant collapses the outer layers begin to spread further from the core making the star grow in volume.

A red giant is much cooler than other stars but also much brighter due to its larger surface area.