A red dwarf is a small, dim, main sequence star of spectral type M (see M
star) or late K (see K star). The characteristic
properties of red dwarfs stem ultimately from their low mass, which is approximately
in the range 0.1 to 0.5 solar mass. Their low surface temperature, in the
range 2,500 to 3,500°C, imparts to them a ruddy hue, while their combination
of low temperature and small surface area results in them being very faint.
The have fully convective interiors, i.e., convective envelopes and convective cores. Many red dwarfs are also flare
|Internal structure of a red dwarf
Red dwarfs survive longer (see stars,
lifetimes of) and are more numerous (see stars,
numbers of) than any other kind of star, with the probable exception
of brown dwarfs. Of the 30 nearest stars
to the Sun, for example, 21 fall into this category (see stars,
nearest). They include:
Like other types of star, red dwarfs may be accompanied by
planets. Indeed, one of the most Earth-like extrasolar
planets discovered to date, in terms of its mass and distance from its
parent star, has been found around the remote red dwarf OGLE-2005-BLG-390L.
However, there are doubts whether any worlds in orbit around such faint
stars could harbor life. These doubts arise because of the extremely small habitable zone that would surround a red
dwarf. Any planet so close to its parent star would almost certainly end
up in a gravitational lock, with one side
permanently turned toward the star. Under such circumstances, it is not
clear whether life would be able to evolve.
|Artist's impression of a red dwarf
|Artist's concept of a young, red
dwarf star surrounded by three planets. Image credit: NASA/JPL-Caltech.