In 1054, astronomers in China recorded a "guest star" that appeared suddenly in the sky, bright enough to be seen in daylight for weeks. What they saw was a supernova — the explosion of a massive star.

This is what's left: a cloud of gas and debris about six thousand light-years away, still racing outward. It's called the Crab Nebula because of a 19th-century drawing that made it look like one.

At its heart is a neutron star — the crushed core of the original star, only around 20 kilometres across, spinning about 30 times a second and sweeping beams of radiation across space like a lighthouse. That pulsar powers the eerie blue glow. The image was stitched together from many Hubble photographs and is one of the largest Hubble ever made.