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Stars

• Stars are born from enormous clouds of gas and dust. The attractive force of gravity between the particles causes the cloud to collapse. Gravitational energy is converted to heat energy and the temperature rises. The temperature gets high enough for hydrogen nuclei to fuse into helium nuclei and release energy (heat and light). The star then becomes a main sequence star as it is in its stable period.

• When the star starts to run out of hydrogen to fuse, it starts to cool and expand and become a red supergiant. It will then contract into a white dwarf and as the light fades, a black dwarf when the star stops emitting light.

• For a massive star, after hydrogen starts to run out, it forms a red supergiant as it cools and expands. The core then contracts under the gravitational force and it becomes hot enough for helium to fuse into oxygen and carbon and the star becomes a blue supergiant as it expands again. The star then contracts and as it collapses it glows exceptionally brightly. It then goes supernova, some of the material is flung out to form a nebula and the star becomes a neutron star.

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