On July 4, 1054, Chinese astronomers in the imperial court looked up and saw a brand-new 'guest star' shining in the constellation Taurus. It was bright enough to be seen in broad daylight for 23 days and remained visible at night for almost two years. Records of the strange star appear in Chinese, Japanese, and Arab observations, and possibly in Native American rock paintings in the southwestern United States.
What those astronomers were seeing was a supernova - a giant star, more than ten times heavier than our Sun, exploding at the end of its life. The blast hurled the star's outer layers into space at millions of kilometres an hour, leaving behind a tiny, fast-spinning core called a neutron star. Today, almost 1,000 years later, astronomers can still see the wreckage. We call it the Crab Nebula - a tangled cloud of glowing gas about 6,500 light-years away.
At the centre of the Crab Nebula spins a pulsar, a city-sized neutron star turning 30 times every second. Its lighthouse beam still flashes past Earth in radio, X-ray and visible light - a leftover heartbeat from a star that died long before any human ever wrote a word.
