Astronomy 2021A/B Lecture Notes - Lecture 11: Galactic Habitable Zone, Rare Earth Hypothesis, Milky Way
9 Dec 2016
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Document Summary
The most basic requirement for a star to be able to support life on orbiting planets is that it be stable long enough to allow that life to originate. This limits us to stars that are in the long-lived, hydrogen-burning phase of their lives. Giants and supergiants are stars that have used up the bulk of their core hydrogen fuel, and undergo substantial change on time scales of millions of years. The spectral sequence obafgkm runs from hot to cool in terms of the surface temperatures of stars. For stars in their hydrogen-fusing phases, this sequence also runs in mass order. O stars are the hottest, most massive, most luminous, and shortest lived. The lifetimes of o and b stars seem too short to permit life to arise on any surrounding planets. A and f stars may live long enough for life to evolve, though probably not long enough for intelligent life.
