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The Sun

The Solar System was formed around 4.6 billion years ago from a large cloud of dust and gas, called a . This collapsed under its own gravity, transferring to in its particles. As the nebula collapsed it became denser, and rotated more rapidly. Collisions between particles caused kinetic energy to be transferred as and . The core of the nebula began to form a hot, dense .

When the Sun’s core became hot enough and dense enough, reactions began, giving out energy and .

A star like the Sun is at equilibrium - gravity tends to pull it inwards, and radiation pressure from the nuclear reactions tends to expand it outwards. In other words, the gravitational collapse is balanced by the expansion due to fusion energy.

The sun in space.

The Sun is currently a star and will remain so for another 4-5 billion years. It will then expand and cool to become a red giant, after which it will shrink and heat up again to become a white dwarf. The white dwarf star will run out of nuclear fuel and slowly cool down over many billions of years.