A colorful crab scuttles across the sky on December nights. It’s faint and far away. But almost a thousand years ago, it announced its birth in dramatic fashion — as a brilliant new star in the constellation Taurus. It was bright enough to see in daylight for several weeks. The Crab Nebula is a cloud of glowing gas that spans about a dozen light-years. It’s called the crab because its tendrils of gas resemble a crab. The nebula was born when a heavy star exploded as a supernova, blasting its outer layers into space. The gas is racing outward at millions of miles per hour, so it’s spread out to form a big cloud. At the center of the nebula is the star’s crushed core — a neutron star. It’s roughly twice as massive as the Sun, but only about as wide as a small city. At such extreme density, a teaspoon of its matter would weigh as much as 10 million African elephants. The explosion that created the nebula also caused the neutron star to spin more than 30 times a second. And it created a ma
