Artwork showing a type of cataclysmic variable star system known as an intermediate polar, or DQ Herculis, star. This system comprises a white dwarf (right) in mutual orbit with a larger red dwarf (left). The strong gravitational field of the dense white dwarf star draws material (hot gas) from its larger companion. This forms an accretion disc around the white dwarf. The white dwarf has a strong magnetic field, however, and sweeps a hole in the centre of the disc. Gas from the inner edge of this accretion ring is channelled towards the white dwarf's poles via 'accretion curtains'. Periodically, this hot gas erupts on the white dwarf's surface, making the star appear much brighter for a short time. They are powerful sources ox UV and X-rays, which is modulated at the spin period of the white dwarf (a few minutes) and at the orbital period (more than three hours).
