The Star So Large a Plane Would Take 1,000 Years to Circle It

Imagine boarding a plane… and dying of old age before it finishes a single lap around this star.

This is Stephenson 2-18 — the largest known star in the universe. Drop it where our Sun is, and its surface would swallow Mercury, Venus, Earth, Mars, the asteroid belt, Jupiter — and stretch past the orbit of Saturn. Our entire inner solar system: gone.

Stephenson 2-18 sits roughly 19,000 light-years away in the constellation Scutum, inside a massive cluster of red supergiants. It's a red hypergiant — a star in the final, bloated chapter of its life, burning so fast it's essentially tearing itself apart. Its radius is around 2,150 times the Sun's — a volume about 10 billion times greater. Put it this way: if the Sun were a golf ball, this star would stand taller than a skyscraper. Stars this huge don't last — hypergiants burn through their fuel in just a few million years, against the Sun's ten billion. When it dies, it'll collapse in a supernova and likely leave behind a neutron star or black hole.

But here's what should keep you up at night. This colossus — the one that makes our Sun look like a speck of dust — is just one star among hundreds of billions in the Milky Way. And the Milky Way is one of roughly two trillion galaxies in the observable universe. The scale never stops.

Follow The Cosmic Vault — the universe is stranger than you think.