Every atom in you heavier than hydrogen was forged inside a star. This page covers what your IGCSE Physics / Co-ordinated Sciences course needs you to know about how stars are born, live, and die — then hands the story back to you. Pick a format below and tell it your own way.
Every star starts the same way. What happens next depends on one number: its mass. Tap a stage on the diagram to read what's actually happening inside the star.
One process explains almost everything on the diagram above: why a protostar isn't yet a star, why stars shine for billions of years without going out, and why you're made of atoms that didn't exist at the birth of the universe.
Nuclear fusion is what happens when two nuclei are forced so close together that they join to form a new, heavier nucleus. In a star, that's hydrogen nuclei fusing into helium nuclei.
Normally, two hydrogen nuclei (both positively charged) repel each other strongly. Only extreme temperature and pressure — the kind you get deep inside a collapsing star — can force them together anyway.
A helium nucleus has very slightly less mass than the four hydrogen nuclei that made it. That missing mass doesn't disappear — it's released as energy.
E = mc²Because c (the speed of light) is so large, even a tiny bit of missing mass releases an enormous amount of energy. That's what makes a star shine.
Fusion pushes outward (heat and radiation pressure). Gravity pulls inward. In a stable main sequence star these two forces are exactly balanced — this is what the syllabus means by a star being "stable."
That balance is why the Sun has shone steadily for about 4.6 billion years instead of collapsing or blowing apart.
Same material, three names. Only one thing changes between them.
A nebula and a protostar can both be hot and glowing — but that heat comes purely from gravitational contraction, particles colliding as they're squeezed closer together. Nothing is fusing. The moment the core reaches roughly 15 million°C, hydrogen fusion ignites, outward pressure switches on, and the object becomes a genuinely stable star. Fusion is the dividing line — it's the difference between syllabus points (b) and (c).
Every element heavier than hydrogen was built inside a star, or in its explosive death.
Every point below is something you could be asked to describe or explain in Paper 2/4 (Extended) or Paper 1/3 (Core). CORE content is for everyone; SUPPLEMENT content is Extended candidates only.
6.2.1Stars are powered by nuclear reactions that release energy; in stable stars, this is the fusion of hydrogen into helium.
(a)A star forms from an interstellar cloud of gas and dust that contains hydrogen.
(b)A protostar is that cloud collapsing and heating up because of its own gravitational attraction.
(c)A protostar becomes a stable star once the inward pull of gravity is balanced by the outward force from the very high temperature at its centre — nuclear fusion has begun.
(d)Every star eventually runs out of hydrogen fuel for fusion.
(e)Most stars then expand into red giants; more massive stars expand into red supergiants.
(f)A red giant sheds its outer layers as a planetary nebula, leaving a white dwarf at its centre.
(g)A red supergiant explodes as a supernova, scattering a nebula of hydrogen and newly-made heavier elements, and leaving behind a neutron star or a black hole.
(h)The nebula thrown out by a supernova can go on to form new stars — matter is recycled.
Use these before you start building your project — they're where the real images, data, and explanations in your final piece should come from. Credit whatever you use.
A clear, exam-focused walkthrough with a short video and diagram — the best first stop for the core sequence.
bbc.co.uk/bitesize →Written for UK secondary students, with real telescope images of nebulae, supernova remnants, and white dwarfs.
schoolsobservatory.org →NASA's rolling hub of stellar evolution articles, images, and discoveries — good for up-to-date examples.
science.nasa.gov →Real Hubble Space Telescope photographs of nebulae, dying stars, and supernova remnants, with the science behind each.
esahubble.org →A collection of downloadable posters, activities, and presentations on stellar life cycles — ideal if you're building a poster or infographic.
nasa.gov →A single clean infographic of the whole sequence — useful as a layout reference, not for copying directly.
jpl.nasa.gov →Same content, your choice of vehicle. Every option below needs to cover the same core science — pick the one that plays to what you're best at making.
One diagram, both branches, labelled clearly enough to teach a Year 7 student in 60 seconds.
Built to actually present out loud, not to be read silently — talk to your slides, don't read them.
Write it like a real popular-science piece — a hook, a clear structure, no bullet points.
Write it to be heard, not read — short sentences, a narrator's voice, timestamps for your own reference.
Numbers do the talking: masses, timescales, temperatures, sizes.
Build it — clay, card, Blender, whatever you've got — then write the science it can't show on its own.
Loosely mapped to the assessment objectives your exam papers use — AO1 (knowledge) and AO2 (explanation and application).
States the correct sequence of stages for both low and high mass stars using the right vocabulary, in the right order. (AO1)
Explains why a protostar becomes stable, why the paths split by mass, and correctly separates Core from Supplement content. (AO1 + AO2)
Brings in something not required — the Hertzsprung–Russell diagram, the Chandrasekhar limit, or how heavy elements like gold and iron are actually made — and explains it accurately.