Astrophysicists are redrawing the textbook image of pulsars, the dense, whirling remains of exploded stars, thanks to NASA's Neutron star Interior Composition Explorer (NICER), an X-ray telescope aboard the International Space Station. Using NICER data, scientists have obtained the first precise and dependable measurements of both a pulsar's size and its mass, as well as the first-ever map of hot spots on its surface.