High-frequency brightness oscillations: This figure, provided by Don Smith of MIT, shows the X-ray intensity variation from an accreting neutron star. The top panel shows the variation in intensity of low-energy X-rays, compared to high-energy X-rays in the bottom panel. In both panels, the vertical axis gives the intensity, and the horizontal axis is a measure of time. The total stretch of time represented by this graph is only about 0.004 seconds!