Stellar mass statistics

I wonder what is the ratio of the number of stars in our galaxy with a
mass comparable to the sum, to the number with a mass one half the mass
of the sun? with a mass twice the mass of the sun? etc. Is there some
kind of power law for these things?

dave wrote:
I wonder what is the ratio of the number of stars in our galaxy with a
mass comparable to the sum, to the number with a mass one half the mass
of the sun? with a mass twice the mass of the sun? etc. Is there some
kind of power law for these things?

What you describe is called the "mass function." As for describing it
with a power law -- if only it were so easy! It's a function of time,
as the more massive stars burn out quickest. It's a function of
location within the galaxy, of how long it's been since there was a
bout of star formation nearby ... it's not an easy problem.

Nevertheless, a power law doesn't do all that badly:
N(M) ~ (M/M_sun)^{-2.35}
at least for stars near 1 M_sun. It's steeper for higher masses and
flatter for lower masses.

You might want to take a look at _Galactic Astronomy_ by Mihalas and
Binney. I have the 2nd edition, from 1981, open to pages 230-231 as I
write this. You can tell roughly how long it's been since I was in
grad school. :-)

Hope this helps, or at least gives you some terms which you can google
for yourself.

-- Bill Owen

"Bill Owen" wrote in message
...
dave wrote:
I wonder what is the ratio of the number of stars in our galaxy with a
mass comparable to the sum, to the number with a mass one half the mass
of the sun? with a mass twice the mass of the sun? etc. Is there some
kind of power law for these things?

What you describe is called the "mass function." As for describing it
with a power law -- if only it were so easy! It's a function of time,
as the more massive stars burn out quickest. It's a function of
location within the galaxy, of how long it's been since there was a
bout of star formation nearby ... it's not an easy problem.


Nitpicking, but neither of these statements is true. Its not a function of
time, as the OP clearly meant right now. Nor is is a function of location
within the galaxy, as the original question simply specifies "our galaxy" -
presumably the whole galaxy.