Supernovae

Most stars fade out quietly. A few end in the biggest explosion there is. It is called a supernova, and for a few weeks that one star can outshine the whole galaxy it lives in.

There are two ways to make one. The first needs a heavy star, more than about eight times as heavy as the Sun. When its fuel runs out, its core is a ball of iron with nothing left to hold it up. The core falls in on itself in less than a second. The fall stops with a jolt, and the rest of the star is blown out into space.

The second way needs a white dwarf with a partner star close by. The white dwarf pulls gas across from its partner and grows heavier. No white dwarf can be heavier than 1.4 Suns. As it nears that weight the whole star catches light at once and blows itself to pieces.

In February 1987 a star blew up in the Large Magellanic Cloud, a small galaxy next door to ours, 168,000 light years away. It was the first supernova anyone had seen without a telescope since 1604. Deep underground, three detectors caught 25 tiny particles called neutrinos, which had come straight from its collapsing core.

A supernova leaves a cloud of wreckage that goes on spreading for thousands of years. The Crab Nebula is the wreck of one that people saw in the year 1054.

We owe these explosions a great deal. Stars make oxygen, silicon and iron inside themselves, and a supernova is what throws them out into space. That gas drifts into new clouds, and new stars and planets form from it. The iron in your blood was made in a star.