Variable star. Artwork of a variable Mira-type binary star system, seen from the surface of a nearby planet. The system, which consists of a large red giant star (left) with a smaller blue companion (right), is similar to the variable star Mira, or Omicron Ceti. The magnitude (brightness) of the red giant may change over time with a regular period. The red giant is a dying star; it has exhausted its supply of hydrogen fuel and is now burning helium. Its more dense companion is accreting material from its outer atmosphere.