GCSE Physics - The Life Cycle Of Stars / How Stars are Formed and Destroyed (2026/27 exams)

Formation of a Protostar00:00:10

Stars begin as a large cloud of dust and gas called a nebula. Gravity pulls this material together to form a protostar. As more particles join, the protostar grows, its gravity strengthens, and it becomes denser and hotter due to increased particle collisions.

Main Sequence Star00:00:54

When the temperature and pressure are high enough, hydrogen nuclei fuse to form helium nuclei in a process called nuclear fusion. This releases immense energy, heating the star's core and marking its transition to a main sequence star. During this long, stable phase, the outward pressure from fusion balances the inward force of gravity, a stage our sun is currently in.

Red Giant or Red Supergiant00:01:45

Eventually, a star runs out of hydrogen fuel, causing the inward pressure of gravity to dominate and contract the star. This increases its temperature and density, allowing nuclear fusion to restart, forming heavier elements up to iron. The star then expands into either a red giant (for small to medium stars like our sun) or a red supergiant (for very large stars).

Life Cycle of a Red Giant00:03:01

A red giant becomes unstable, expelling its outer layers of dust and gas. What remains is a hot, dense solid core called a white dwarf, which no longer undergoes nuclear fusion. Over time, the white dwarf cools and darkens, eventually becoming a black dwarf as it loses all its energy and no longer emits light.

Life Cycle of a Red Supergiant00:04:00

Red supergiants continue nuclear fusion, shining brightly and undergoing several cycles of expansion and contraction. They ultimately explode in a supernova, ejecting elements heavier than iron across the universe. The remnant depends on the star's initial size: a very large star forms a neutron star, while an absolutely massive star collapses into a black hole, an incredibly dense object whose gravity prevents light from escaping.

Summary of Star Life Cycles00:05:04

Stars begin as nebulae, form protostars, and then become main sequence stars through nuclear fusion. After exhausting hydrogen, they become either red giants (small/medium) or red supergiants (large). Red giants evolve into white dwarfs and then black dwarfs. Red supergiants explode in a supernova, leaving behind either a neutron star or a black hole, depending on their mass.