# Assuming that you have the mass and age of a star, can you determine the most likely current class?

I am asking for the purposes of generating realistic stars. Assuming that you have the inputs of the mass of a star, and its age, is there any method for determining its class and state?

• We do that without exact knowledge of age and mass, by observation. Classification is based on observation and derived from observations - what is the question then. – MolbOrg Sep 2 '16 at 19:01
• At issue is an unobservable star that does not actually exist, where for the purposes of simulation some mass is said to have formed some period of time ago. The output being looked for is what it would have the strongest likelihood of being after some period of time. – Wilma McAfee Sep 2 '16 at 19:52

The Herzsprung-Russell diagram, plotting luminosity against color.

I think/hope this picture might answer your question. Class is listed at the top horizontal axis but I am not sure what you mean by "state", I am guessing you mean red giant, white dwarf etc.

For main sequence stars, the line running right to left, bottom to top, the luminosity mass relation is show below. As the stars age, depending on their mass, they go off the main sequence

For red giants and white dwarves, this relation below is not valid.

A white dwarf is formed when a low-mass star has exhausted all its central nuclear fuel and lost its outer layers as a planetary nebula.

A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature as low as 5,000 K and lower.

The main sequence relationship is represented by the equation:

${\displaystyle {\frac {L}{L_{\odot }}}=\left({\frac {M}{M_{\odot }}}\right)^{a}}$

where $L_⊙$ and $M_⊙$ are the luminosity and mass of the Sun and 1 < a < 6.1 The value a = 3.5 is commonly used for main-sequence stars.

• This is great, thank you so much. You are correct as to what I meant by state, as a world generated entirely with main sequence objects isn't realistic. You mentioned that as stars age, depending on their mass, that they go off the main sequence. Is there any generalized relationship known for this that can be used for approximations? – Wilma McAfee Sep 2 '16 at 19:55
• Instead of my waffling, here are 2 good links universetoday.com/25160/how-long-do-stars-last which has 3 good informative podcasts at the end if you scroll down and en.wikipedia.org/wiki/Stellar_evolution. Please don't forget, above a certain mass, some stars are doomed to become black holes, which are not on the chart. Best of luck with it. – user108787 Sep 2 '16 at 20:06