Using the Chandra X-ray Observatory to learn more about pulsars, A team led by Stephen Murray of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., studied 3C58, the remains of a supernova observed on Earth in 1181 AD in the constellation Cassiopeia. 3C58 is one of the youngest known pulsars, and behaves quite differently from the better known pulsar in the Crab Nebula, which is about the same age. The observations of 3C58 will enable scientists to better understand how neutron stars are formed in the seconds just before a supernova explosion, and how they pump energy into the space around them for thousands of years after the explosion. 3C58 is a neutron star rotating 15 times a second, which means it is rotating at about half the rate of the Crab Nebula pulsar. The 3C58 pulsar is rotating almost as fast as it was when it was formed. In contrast, the Crab pulsar was formed spinning much more rapidly and has slowed to about half its initial speed. Conventional theory has assumed that all pulsars were like the Crab, but the observations of 3C58 have cast doubt on that assumption.