At the heart of the Crab Nebula lies an incredibly dense neutron star — one with the same mass as our sun, but packed into a space the size of a small town, just a few miles across — left over from the star that exploded. It pulses like a beating heart, spinning 30 times a second and shooting out blistering pulses of radiation like clockwork. These rapidly spinning stars are known as pulsars, which are such accurate cosmic timekeepers that astronomers can use them to measure other phenomena. Interruptions in the pulses can be used to detect gravitational waves, for example.
The Crab pulsar is pictured in the center of the new image (it's the upper right star in that bright center pair). It's surrounded by the gaseous outer layers of the nebula, blasted into space when the dead star went supernova and left its dense core behind. The wispy trails forming an expanding ring around the star are moving at half the speed of light. The Crab Nebula is one of the most frequently imaged objects in our galaxy, but this is the first photo to showcase its violent, pulsing heart.