About half of all stars are binaries. In some cases we can use Newton's Law of Gravity to get masses. Mass determines the lifetime of a star. We might expect more massive stars to live longer since there is more fuel for fusion. However this is not the case.
More massive stars burn their fuel faster and live shorter.
This is 1000X longer. So massive blue stars on the main sequence are generally babies compared to the red stars of the main sequence. Can find star formation places by finding blue stars. Information contained on this page does not represent the lecture verbatim. These notes are not a substitute for class attendance.