# What are the equations governing stellar evolution (Luminosity, Mass, Temperature, Radius)

I'm looking for ('simplified') equations governing stellar evolution. Especially how mass, luminosity, temperature and radius of a star change during it's lifetime. As well as equations which tell you how long a star stays in a certain stellar stage (PMS, MS, ...).

Extra clarification by example:

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After that a star with a mass between x and y enters the main sequence for a duration of $\Delta T = formula$. During this phase it's mass changes according to $M = formula(t)$. after that it enters the xxx phase

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For those who think this question is to broad, please give some suggestions, 'google terms', ... from which I can move forward.

• Question is too broad. You appear to be looking for universal relations that apply to these quantities, but there aren't any that apply to other than narrow mass ranges and narrow definitions of evolutionary phases. The equations that "govern stellar evolution" are the well known (differential) equations of stellar structure, that must be solved for cases of interest. – Rob Jeffries Aug 2 '18 at 17:20
• what are those well known (differential) equations – Sam Coutteau Aug 2 '18 at 17:27
• Do these help course notes and lecture on equations of stellar structure help ? Note that there is a lot of work needed to turn the equations into a computer program that can solve them and get testable output from them... – astrosnapper Aug 2 '18 at 17:57
• I don't think we should be discouraging people from asking questions which unbeknownst to them have complicated answers. As such, I don't think this question is too broad. Having said that, from what I understand of stellar dynamics (which is comprised mainly of wikipedia articles), it is really complicated and star-specific. I'd go as far as to say that there are more types of star than there are planet, and the heavier the star, the more complicated the evolution. – Ingolifs Aug 3 '18 at 0:06
• en.wikipedia.org/wiki/… – Rob Jeffries Aug 3 '18 at 3:26