Red dwarfs are small (less than half the size of our sun), cool stars (less than 4000 K). Taken together, these properties make the stars difficult to find from any distance. Until recently, all the red dwarfs that had been identified were within our own galaxy. Not unreasonably, astronomers assumed that other galaxies would have a similar number of red dwarfs. This did not turn out to be the case.
Pieter van Dokkum of Yale University and Charlie Conroy of the Harvard-Smithsonian Center for Astrophysics have found that some nearby elliptical galaxies have as many as 20 times more red dwarfs than does our Milky Way galaxy.
Filtering out the light from brighter stars, astronomers detected the faint signature of small, dim red dwarf stars in nearby elliptical galaxies (right), and found these are much more numerous than in our own Milky Way (left). This finding suggests that the total number of stars in the universe could be up to three times higher than previously thought.
Illustration by Yale UniversityOne reason scientists are interested in red dwarfs is that they burn through their fuel at an extremely slow rate, maintaining constant heat and luminosity all the while. This means that any planet with the potential to develop life that happens to be orbiting a red dwarf would have hundreds of billions of years to do so. Life on such a planet would have more than enough time to go from single-celled to civilization. And now we know there are lots more of these stars around.