A shock wave, possibly from a nearby supernova, causes a cloud of gas and dust to collapse under its own gravity. The Solar System began forming about 5 billion years ago. Then it was just a small part of a vast cloud of gas and dust, measuring about 65 light years across, that drifted through the Milky Way Galaxy. The cloud had probably formed in a region where large stars, including supergiants, were being created—a region possibly quite similar to the Orion Nebula. A supernova, an exploding supergiant star, may have sent massive shock waves racing across space, striking the cloud. The impact may somehow have been sufficient to trigger the cloud's collapse under its own gravity. The massive amount of gas and dust started to spiral inwards.
Formation of the Sun
Within 100,000 years of the shock wave's impact, the collapsed cloud became a swirling disc, called a solar nebula. Under pressure from gas and dust spiralling inwards, the centre of the disc became hotter and denser and began to bulge. It was now what is called a protostar, a "star" in which nuclear fusion at its core was yet to begin. It would soon evolve into a true star, the infant Sun.
In about 5 billion years, the Sun will cool and expand to become a red giant, before casting off its outer layers to become a tiny remnant star known as a white dwarf. Billions of years into the future, the surviving planets will be captured or destroyed by the gravity of other nearby stars.
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