Stellar Classification Assistance

[Solauren]

Hello.

I'm trying to figure out the percentages of each type of Star in the universe (including things like Neutron Stars, Pulsars, Black Holes, etc). It's for a game I've been thinking about on an off. I'm trying to do realistic star generation.

Does anyone know somewhere I can look where it's easy to follow? Like, not Wikipedia?

I have the percentages for Main Sequence stars (within the Main Sequence), but not for the rest.

Thanks

[Junghalli]

Red dwarfs are 70% of stars.

http://www.solstation.com/stars/pc10rds.htm

[Wyrm]

Your question is both simple and complicated. I don't think anyone's ever calculated a universe-wise census of the stars, as investigating the distribution of stars in clusters is more interesting and important. However, the problem does break down easily into several steps.

The properties (especially spectral class and lifetime) and ultimate fate of a star depends almost entirely on its mass (and also metallicity, but never mind that now), so if you know the initial distribution of stars when the cluster forms, you can then find the distribution of all the interesting objects formed from them. Looking at Hertzsprung-Russell diagrams for clusters of various ages will give you a rough idea of how a cluster's stars evolve with age, and how many stars are at each stage. Also, the Miller-Scalo initial mass function (IMF) will tell you the approximate distribution of initial masses for a modern cluster.

However, the IMF varies with the metallicity of nebula, and therefore, on the age of the galaxy and the universe. The metal-poor early universe had an overabundance of crazy huge stars, because of the lack of metals in the early universe. The presence of metals makes the radiation of heat more efficient, and the radiation of heat is what blows away the nebula the star forms in and stops its growth. Only after the metallicity of the stars approaches modern values do you get a modern distribution of initial star masses.

Furthermore, the proportion of stars depends on the type of galaxy you're considering. In elliptical galaxies, star formation stopped early, so the stars are metal-poor (though not excessively so) and old — they have approximately the distribution of stars you'd find in a globular cluster. Spiral galaxies have stars varying by Population — stars in the disk are usually young, stars in the nucleus and in globular clusters are old. The older the star, the smaller and redder. (The irregular galaxies are just oddballs: assume that they're just big open clusters.)

Time in the Red Giant stage (for a low-mass star) varies, but about 10 million years is a good round number. After that, the star proceeds rapidly to the white dwarf stage. (I believe 10% of all stars are white dwarfs; there aren't more because the universe isn't old enough to accumulate many of them.)

That's enough to get started. It's too late in the evening for a more detailed information hunt.

By the way, you can count on all neutron stars being pulsars to someone.