Mira double star system, Chandra X-ray telescope image. The system comprises Mira A (right), a huge red giant, and Mira B, a tiny white dwarf. Material from the red giant is attracted to the extremely dense white dwarf by its powerful gravity, and emits X-rays as it is accelerated and heated in an accretion disc around it. The two stars are separated by around 12 billion kilometres. Mira (Omicron Ceti) is a variable star. The regular pulsations in size of the red giant mean that it varies in brightness by a factor of around 1700 over a period of 331 days. It lies around 420 light years from Earth in the constellation Cetus. Image taken on 6th December 2003.