The smallest stars can burn for up to 10 trillion years and never swell up
They sip their fuel so slowly they are the most common stars in the universe, and one of our closest neighbors is one you cannot see without a telescope.
Kurzgesagt – In a Nutshell · The Largest Star in the Universe – Size ComparisonThe smallest true stars, called red dwarfs, can burn for up to 10 trillion years, or roughly a thousand times longer than the universe has existed, and they never swell up when they die.
With roughly the mass of a hundred Jupiters combined, they are barely heavy enough to fuse hydrogen into helium, the reaction that makes a star shine. Because they are so light, they stay small, cool, and dim, and burn through their fuel extremely slowly, which makes them by far the most common type of star in the universe.
They are the only main-sequence stars that fizzle out rather than swelling up when they die. One of them, Barnard's Star, counts among Earth's nearest stellar neighbors, yet needs a telescope to be seen.
Questions people ask
How does that lifetime compare with our Sun?
The Sun is expected to live about 10 billion years in total, with about 5 billion years left. A red dwarf that lives 10 trillion years would last roughly a thousand times longer, far into a future when most other stars have already died.
What does it mean to fizzle out instead of swelling up?
Most stars eventually run low on hydrogen, shrink in the center, and puff up their outer layers into giants. Red dwarfs mix their gas so thoroughly and burn so slowly that they never get that puffed-up phase, and theory says they will simply fade into small, dense embers called white dwarfs.
If red dwarfs are so common, why can't I see any?
They are common but very dim, because their surfaces are cool and they put out little light. Even nearby ones like Barnard's Star, about six light-years away, need a telescope to be seen, while brighter, rarer stars dominate the night sky.