This animation illustrates the direct relationship between a pulsar’s X-ray pulses and its quasi-periodic oscillation (QPO), an X-ray source originating near the inner edge of an accretion disk and shown here as a white patch. When the QPO orbits more slowly than the pulsar’s spin, the magnetic field of the neutron star inhibits some gas from flowing onto hot spots at its magnetic poles, dimming the X-ray pulses.