An artist's depiction of the life stages of our Sun, from birth to death as a white dwarf within a planetary nebula. Image credit: ESO/S. Steinhöfel.
It all started with a giant cloud of gas, some 4.57 billion years ago. This cloud of helium and hydrogen collapsed under its own gravity and formed a protostar. After 100,00 years, it became a fully formed star and began its hydrogen burning phase, otherwise known as its main sequence — its adulthood of sorts. This lasts a total of 10 billion years. Currently, our Sun is halfway through its main sequence stage. Even now, however, the Sun is going through changes, but they are indiscernible over a human lifetime. Every billion years, our star gets 10% brighter, as it marches towards the end of its life. Because of this, the Earth’s surface will be too hot to sustain liquid water, and, in all likelihood life, in one billion years. To make matters worse, the Sun is expected to swell up to a few hundred times its current size in 5 billion years, when it becomes a red giant. At this point, it will have swallowed up Mercury, Venus, and possibly even Earth!
In one final gigantic tremor, our red giant Sun will expel its gaseous outer layers, forming an expanding planetary nebula, and leaving only a faint white dwarf at its centre. The layers of the planetary nebula will sweep through our Solar System and reach the interstellar medium, where they might one day join a gas cloud and lead to the formation of another star. As with the living creatures on Earth, we observe a beautifully cyclic nature in the lifespan of stars.