A neighbourly red giant

Red giants may become unstable and exhibit variable luminosity: the red giant Mira (Omicron Ceti) displays a variation in luminosity by a factor of 10,000 over a period of 11 months and can be seen with the naked eye when at maximum brightness. The diameter of the star’s atmosphere changes by roughly 100 million kilometres during the cycle of pulsation.

Observations have also noted a giant flare from the star. Mira is part of a contrasting binary system consisting of two stars, both with similar masses to the Sun, one a white dwarf, the other a red giant. It is speculated that such flares may be one mechanism by which heavier elements such as carbon, oxygen and nitrogen that are produced in fusion in red giants are distributed in the universe.