Back to: Astronomy & the Cosmos
Every star eventually exhausts its core fuel, and what happens next depends on mass. A Sun-like star swells into a red giant, when our turn comes in about 5 billion years the Sun will engulf Mercury and Venus and roast Earth, then gently sheds its outer layers into a glowing shell and retires as a white dwarf: an Earth-sized ember so dense a teaspoon of it would weigh tons, cooling quietly for eternity.
Massive stars go out spectacularly. When a star more than about eight times the Sun’s mass runs out of fuel, its core collapses in under a second and the star detonates as a supernova, briefly outshining its entire galaxy of billions of stars. What remains is either a neutron star, a city-sized sphere so dense a teaspoon would weigh billions of tons, sometimes spinning hundreds of times per second, or, for the most massive cores, a black hole.
Here’s the part that should change how you see your own hands: fusion inside stars and the violence of supernovae forged nearly every element heavier than hydrogen and helium, the carbon in your cells, the calcium in your bones, the iron in your blood, the oxygen you’re breathing. Those elements were scattered into space by dying stars and later gathered into the Sun, the Earth, and you. Carl Sagan’s line is literal science: we are made of star stuff.