Star Types - Stellar Classification, Habitability, and The Search For Life

Stellar Classification, Habitability, and The Search For Life

Humans may eventually be able to colonize any kind of stellar habitat, this section will address the probability of life arising around other stars.

Stability, luminosity, and lifespan are all factors in stellar habitability. We only know of one star that hosts life, and that is our own; a G-class star with an abundance of heavy elements and low variability in brightness. It is also unlike many stellar systems in that it only has one star in it (see Planetary habitability, under the binary systems section).

Working from these constraints and the problems of having an empirical sample set of only one, the range of stars that are predicted to be able to support life as we know it is limited by a few factors. Of the main-sequence star types, stars more massive than 1.5 times that of the Sun (spectral types O, B, and A) age too quickly for advanced life to develop (using Earth as a guideline). On the other extreme, dwarfs of less than half the mass of the Sun (spectral type M) are likely to tidally lock planets within their habitable zone, along with other problems (see Habitability of red dwarf systems). While there are many problems facing life on red dwarfs, due to their sheer numbers and longevity many astronomers continue to model these systems.

For these reasons NASA's Kepler Mission is searching for habitable planets at nearby main-sequence stars that are less massive than spectral type A but more massive than type M – making the most probable stars to host life dwarf stars of types F, G, and K.