- The kinetic energy of the particle's activity turns to heat and the sphere starts to glow, so soon it becomes a protostar.
- At 3, 000 kelvin, protostar's core will be hot enough for its atom to ionise, leaving only positively - charged hydrogen and helium nuclei.
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A Star is born
- The compression exerted by the surroundings, mass continues to increase. If enough mass gathers, the force of gravity exceeds the force of repulsion between the hydrogen nuclei and makes the nuclei 'fuse'.
- This produces helium and an awful lot of heat - which sustains the hydrogen fusion.
- At last a star is born.
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Main Sequence Stars
- Stars spend most their active lives in a stable state fusing hydrogen to helium. This stable state is known as the star's main sequence.
- The Sun for example is a main sequence Star. It has about 5 billion years and will do so far about another 5 billion years.
- Bigger stars fuse hydrogen to helium faster and live shorter lives.
- Smaller star fuse hydrogen to helium slower and live longer lives.
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- Sooner or later, a main sequence star's core starts to run out of hydrogen. Making the star to expand to perhaps 1000 times the volume of the Sun. In about 5 billion years the sun itself will expand and consume Mercury and Venus and maybe even the Earth.
- Being bigger but with fewer core reactions means that the star's surface cools to about 3, 000 kelvin and turns to a deep red colour. The star also produces silicon, oxygen, carbon and iron.
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