The Story of Supernovae — a Star's Glorious End and the Origin of Our Bodies
A supernova is a colossal explosion in which a single star can outshine an entire galaxy. Discover how the glorious death of a massive star scatters the elements that go on to build new stars, new planets, and even our own bodies.
Stars die, too
Stars are not eternal. A star shines by fusing hydrogen into helium at its core, and when that fuel runs out its balance collapses and its life comes to an end. A lightweight star like the Sun swells up quietly, sheds its outer shell, and cools into a white dwarf — but a star more than eight times the mass of the Sun meets an utterly different fate: a titanic explosion known as a "supernova."
In a single instant a supernova can pour out billions of times the light of the Sun, sometimes rivaling an entire galaxy. That is why people of old, seeing a brilliant star suddenly appear where nothing had been, called it a "new star" (nova).
The moment the core collapses
Even after burning through its hydrogen, a massive star goes on fusing helium, then carbon, then oxygen, forging ever heavier elements. But once it reaches iron it can release no more energy, and the core, unable to support its own weight, collapses in an instant. A core the size of the Earth is crushed to the size of a city in less than a second, and the recoil hurls the star's outer layers into space at thousands of kilometers per second — this is a "core-collapse supernova."
Depending on its mass, the leftover core becomes either a "neutron star" (an ultra-dense star in which a single spoonful weighs billions of tons) or, if heavier still, a "black hole" from which not even light can escape.
We are made of stardust
Supernovae matter not merely because they are spectacular. Heavy elements like gold, silver, and iron are forged in bulk and flung across the universe only in the extreme instant of a star's explosion. The iron in our blood, the calcium in our bones, the gold in the ring on our finger — all of it is ash left behind billions of years ago when some star blew apart as a supernova.
As the astronomer Carl Sagan put it, we are quite literally made of "star stuff." The elements a supernova scatters gather again into new stars and planets, and on one of them — the Earth — life was born.
Supernovae recorded in history
In 1054, astronomical records from Goryeo, China, and the Arab world describe a "guest star" appearing in Taurus so bright it could be seen even by day, then fading away. On that very spot today lies the "Crab Nebula (M1)," the wreckage of that explosion. "Tycho's Star" in Cassiopeia in 1572 and "Kepler's Star" in Ophiuchus in 1604 were the events that led early modern astronomy to question whether the heavens were truly unchanging.
The closest recent supernova is SN 1987A, which exploded in the Large Magellanic Cloud in 1987. And Betelgeuse in the winter constellation of Orion is already near the end of its life, drawing attention as the next candidate to explode as a supernova "soon" in astronomical terms.