How long is a star's generation?

[plutocrass]

What is the lifetime age of each generation of stars, and what is meant by a third generation star, such as the sun? Is there a fourth generation?

 

[Saiph]

This isn't as cut and dried as you might hope. Larger stars live faster, die faster. Large blue stars can live from millions of years to hundreds of millions. You get to yellow stars, and you're soundly in the "billions" of years lifespan. Small red dwarf stars can live for (theoretically) hundreds of billions.<br /><br />The "generation" of a star is normally a way of referring to how much "metal" is in the star. Since the cosmological abundance of material is 25% helium, 75% hydrogen, and any other elements (the "metals") are created in stars, this is a pretty good indicator.<br /><br />A first generation star has no metal content (or absolutely minimal). This is because no stars existed before it, to spew star-made metals into the nebula this star formed from. These are also called population III stars, of which we've found very, very few.<br /><br />A second generation star has little metal content, but some, because a lot of the first stars around spewed metals into the nebulae it formed from. These are Population II stars, often found in globular clusters where star formation hasn't really occured since the cluster formed 10+ billion years ago.<br /><br />Third generation have pretty typical metal contents, they're found in active star forming regions in galaxies (read disks and arms of spiral galaxies)...it's the typical star. This is a population I star. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[nexium]

The idea of generations of stars, and population 1, 2 and 3 likely preceded most of the fusion theory. In the usual definition of generation there were likely a few 4th generation stars 13 billion years ago. Astronomy redefines generation as Saiph explained, so no 4th generation stars. Neil