Most stars, including the Sun, spend most of their lives quietly fusing hydrogen.
A star spends about 90% of its life on the so-called main sequence, quietly fusing hydrogen into helium in its core. The outward pressure of the hot gas balances the inward pull of gravity, so the star stays stable.
Mass is everything
The mass of a star determines its temperature, colour and lifetime. Massive stars are hot, blue and burn their fuel quickly. Small stars are cool, red and use their fuel very slowly.
- A star with 10 times the mass of the Sun lives for only a few tens of millions of years.
- The Sun will stay on the main sequence for about 10 billion years in total.
- The smallest red dwarfs can shine for trillions of years, much longer than the current age of the universe.
The image above shows Westerlund 2, a young cluster of about 3,000 stars, roughly 20,000 light-years away. It was released to celebrate the 25th anniversary of the Hubble Space Telescope.