Mira, Mira

Truly the fairest one of all, the “comet” above is an aging red-giant star named Mira. Although Mira has been studied for more than 400 years, its tail has just been discovered by Caltech’s Galaxy Evolution Explorer (GALEX) spacecraft. Shed from Mira’s surface over the last 30,000 years, the tail contains carbon, oxygen, and other elements that will eventually be recycled into new stars and planets—enough material, in this case, to form at least 3,000 Earths or nine Jupiters. Most stars travel at more or less the same speed as the interstellar gas around them, but Mira is hurtling along at a relative velocity of 130 kilometers per second, piling up a “bow shock” whose hot gas mixes with the cooler hydrogen being shed by the star. As this hydrogen swirls away in a turbulent wake, the atoms fluoresce in the ultraviolet. The tail of gas and dust stretches 13 light-years across the sky—for comparison, Proxima Centauri, the nearest star to our sun, is only about four light-years away.

Mira, a pulsating variable star 350 light-years from Earth, will be bright enough to see with the naked eye in mid-November. It lies, appropriately enough, in the tale of Cetus, the whale.

Professor of Physics Christopher Martin, GALEX’s principal investigator, is the lead author of a paper announcing the discovery in the August 16 issue of Nature. —DS