Alexander Brown 4W Physics
Star Definitions
- Red giants: although the core of a star gradually shrinks as it exhausts its hydrogen supply, the star itself begins expanding. It resorts to burning the hydrogen in a shell around its helium core, which inflates the outer layers of its atmosphere. Eventually, the star expands into a red giant, possibly attaining a diameter from 10 to 1,000 times the diameter of the Sun. For example, in its red giant stage, the Sun will expand to the size of the orbit of Earth or beyond and become 2,000 times brighter than it is now. The shrinking core increases the star's internal pressure. The increase in pressure makes the star's temperature increase again until it is hot enough to trigger nuclear reactions between previously inert helium nuclei present in the star. This new series of nuclear reactions releases more energy and the star's core stops contracting. At this point, the star's outer atmosphere begins to contract.
