Proposed explanation for kilohertz oscillations The cartoon above is a sketch of my explanation for the phenomenon of rapid brightness variations. Remember that the matter flows onto the neutron star through an accretion disk. In this picture, we are looking down on the disk as matter flows onto the neutron star (central blue circle), and the grey background indicates that matter is flowing everywhere in that disk. However, in some places the density of matter in the disk is higher, and we have clumps (red oval). Gas from the clump spirals onto the star, and when it hits the star it produces a bright arc (yellow arc). As the clump orbits around the star, the arc of impact moves around the star at the same rate. An observer on the side only sees the arc when the neutron star doesn't block it. Thus, she sees the X-ray intensity go up and down at the rate with which the arc moves around the star, which is the rate with which the clump orbits around the star.