This deep dive covers Birth: How Stars Form within Life Cycle of Stars for GCSE Physics. Revise Life Cycle of Stars in Space Physics for GCSE Physics with 13 exam-style questions and 12 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 2 of 14 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 2 of 14
Practice
13 questions
Recall
12 flashcards
🚀 Birth: How Stars Form
Figure 1: Star formation from a nebula — gravity contracts gas and dust until the core is hot enough for hydrogen fusion to begin
All stars begin in the same way — from a nebula, a vast cloud of gas (mainly hydrogen and helium) and dust, scattered across space.
From Nebula to Main Sequence
- Nebula: A cloud of gas and dust, millions of kilometres across. Gravity very slowly begins to pull material together, but the cloud is so large this takes millions of years.
- Protostar: As material collapses inward, gravitational potential energy converts to kinetic energy — the gas heats up. The collapsing, heating central region is called a protostar. It is not yet a true star because nuclear fusion has not started.
- Main sequence star: When the core temperature reaches about 10 million degrees Celsius, hydrogen nuclei have enough kinetic energy to overcome their mutual electrostatic repulsion and fuse together. Four hydrogen nuclei fuse to form one helium nucleus, releasing enormous amounts of energy. This outward radiation pressure exactly balances inward gravity — the star is now stable and in equilibrium. This is the main sequence, and a star spends most of its life here.
Our Sun has been on the main sequence for about 4.6 billion years and will remain there for another 5 billion years or so.