IP Pegasi. The accretion disk surrounding the white dwarf has been shown to have a spiral pattern. The disk itself is smaller than the Sun's diameter, so the spiral pattern can't be imaged directly by telescopes. Instead, the spiraling disk of gas is mapped over a series of observations using a spectroscopic technique known as Doppler tomography. The left panel shows a tomogram, the directly measured gas velocity map for the system. The relative brightness corresponds to the intensity of light emitted by hydrogen gas moving at the indicated velocity. The position at the centre of this panel represents the velocity of the binary system's center of mass. In the middle panel, a simple model velocity field consistent with the measurements is shown. At the right, the calculated position map of the IP Pegasi accretion disk reveals a two-armed trailing spiral pattern. Credit: D. Steeghs, E. Harlaftis, K. Horne, Astronomy Group, Univ. St. Andrews.