# Astronomy, Luminosity of 100 solar mass stars

jmm5872
This is just a small part of one of my problems. I need to find the luminosity of a stellar population containing 100 solar mass stars and one 20 solar mass star.

I think that the 20 solar mass star will dominate, but I am not sure. Here is the formula to use:

L/Lsun = (M/Msun)^3.5

I am going to have to find the luminosity of the 100 stars, and the 20 solar mass star seperately, and then add the luminosities together. But I am not sure if I can do this...

L/Lsun = (100 Msun/1Msun)^3.5

Or would it simply be 100 Lsun is the total luminosity?

Also, I was not really sure whether to put this question here, or in the other sciences section. I figured this was more related to physics than other sciences.

## Answers and Replies

Staff Emeritus
Gold Member
I am going to have to find the luminosity of the 100 stars, and the 20 solar mass star seperately, and then add the luminosities together. But I am not sure if I can do this...

L/Lsun = (100 Msun/1Msun)^3.5

No. This would be the luminosity of a single 100 M$_\odot$ star.

Or would it simply be 100 Lsun is the total luminosity?

Yes. One hundred separate 1 M$_\odot$ stars would have a combined luminosity of 100 L$_\odot$. That is because each of them would have an individual luminosity of 1 L$_\odot$. Just plug 1 M$_\odot$ into your mass-luminosity relation in order to see that the sentence before this one is true.

Staff Emeritus
Gold Member
Also just a note on your terminology. Most astronomers would parse your phrase "100 solar mass stars" as being equivalent to the phrase, "stars having a mass of 100 M$_\odot$." In order to say what you actually meant, you'd have to say:

One hundred 1 solar-mass stars

or something like that.

jmm5872
Thank you!