By taking a naked-eye inventory of the night sky, one might conclude that our galaxy is inhabited mostly by stars whose masses range from about one to two solar masses M⊙. But that’s highly misleading. The eye’s wavelength range of light sensitivity—approximately 0.4–0.6 µm—makes us miss out on the galaxy’s most numerous class of stars. With eyes sensitive to longer wavelengths in the near-IR, we’d see an entirely different type of star filling the night sky: the red dwarfs.
The masses M of red-dwarf stars range from 0.1 to 0.5 M⊙, and their radii are roughly proportional to M. Their surface temperatures are about half the Sun’s 6000 K. But the process of radiative diffusion, by which the energy generated in the stellar core works its way to the surface, and the requirement of hydrostatic equilibrium dictate that the radiant power output of a star...
