The dwarf that breaks the rules

摘要

The bizarre behaviour of a fast-spinning red star in the constellation of Pisces has confounded astronomers. Not only is it rotating at an extraordinary speed, but this rapid rotation has failed to create the expected magnetic activity. Normally, rapid rotation in a cool star— one that is yellow, orange or red—amplifies the star's magnetic field. This in turn triggers large starspots, flares and other activity. Fast-spinning yellow, orange, and red stars are always very active, whereas the Sun, which completes a rotation once a month, exhibits weak magnetic activity. Gibor Basri and Geoffrey Marcy of the University of California at Berkeley have discovered that this rule is violated by a faint, red star known as BRI 0021-0214. The star is 40 light years from the Earth and probably has no more than a tenth of the Sun's mass. It may be a red dwarf, a star in which hydrogen is fused into helium at a much slower rate than that in the Sun. Seventy per cent of all stars in our Galaxy are red dwarfs.