science & techESA/Hubble
A star's mass decides how long it lives, from tens of millions of years to trillions
A star's mass sets its entire life story. Massive stars burn very bright and very hot, using up their fuel in only tens of millions of years before they die young and often explosively. Stars like the Sun are more measured and last roughly ten billion years. Small red dwarfs burn so slowly that they are expected to shine for trillions of years, far longer than the universe has existed so far.
Stars shine by fusing hydrogen in their cores. Gravity squeezes a heavier star harder, so its core runs hotter and fuses fuel much faster, burning through its supply quickly. A small star has less fuel but burns it so slowly that its supply lasts for an extraordinarily long time.
Mass is the single biggest factor in a star's fate, so the stars we see in any region are a snapshot of different ages and sizes. Astronomers use this link between mass and lifetime to estimate the ages of star clusters and galaxies. It also explains why the universe's oldest surviving stars are small ones, while the heavy stars that forged most heavy elements have already gone.
