Paul S. Ray

A neutron star is a sphere the size of a city but with the mass of the Sun. A single teaspoon of its material would weigh as much as a mountain. The star PSR J0030+0451 spins hundreds of times per second and emits narrow beams of X-rays. When a beam sweeps past Earth, we see a brief flash, like the light from a lighthouse.

The lighthouse in the Crab Nebula blinks thirty times per second. It's a pulsar — a dead star that, as it spins, shoots out narrow beams of light, and Earth sweeps through them like a ship crossing a lighthouse beam. This lighthouse has two beams: the main pulse and the interpulse.