B What is the oldest of each class of star?

[plin092]

TL;DR Summary

When did each stellar class of star start to form.

Hello! I would appreciate it if anyone could help me figure this out. I’ve been struggling to find info on my own but so far nothing’s turned up. I am a little confused on the timeline of the generations of stars. I know that our sun is considered an early Population I star.

However, I could have sworn I also remember that the different classes of stars started to first form at different times. So Class B stars first started to form __ billion of years ago, with Class A _ billion years after that, and Class O _ billion years after that. And that our sun, having formed 4.6 billions years ago, is one of the oldest G class stars.

(This doesn’t mean that there were absolutely no instances of lower class stars before these times. But they were extremely rare and only started to be commonly at these dates.)

But, when searching now, I cannot find any of these times online. Which has me thinking I may be mistaken. Is this idea correct, or have all classes formed the same as they do now after the first generation of stars? And if it is correct, when did each class of star start to form?

 

[Drakkith]

However, I could have sworn I also remember that the different classes of stars started to first form at different times. So Class B stars first started to form __ billion of years ago, with Class A _ billion years after that, and Class O _ billion years after that. And that our sun, having formed 4.6 billions years ago, is one of the oldest G class stars.

No, stellar class is unrelated to time of formation. The first stars were population III stars, with very low metallicity and likely a higher average mass than current stars. But they still fell into virtually all the different stellar classes.

Note that stellar classification, specifically the Harvard spectral classification, is based on temperature and photospheric composition, so a population III star with a surface temperature of 20,000 K and a population I star with a surface temperature of 20,000 K are both class B as far as I know. Someone correct me if I'm wrong please.

 

[PeterDonis]

I could have sworn I also remember that the different classes of stars started to first form at different times.

You might be thinking of the lifetime of a star on the main sequence, which does depend on stellar class. More massive/luminous main sequence stars have shorter lifetimes on the main sequence. But this has nothing to do with time of formation.