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The Question
(Submitted October 29, 1997)
I teach astronomy, and a student once asked me which
there are more of in our galaxy -- Pop. I stars or Pop. II stars.
I wasn't sure! Do you know? More
specifically, what is the ratio of the number of Pop. I
stars to the number of Pop. II stars in the galaxy?
The Answer
According to 'Galactic Dynamics' by Tremaine and Binney (1987: Princeton)
the ratio of luminosities of the spheroid population to the disk population
is 1/30. In order to translate to numbers of stars, we can use the fact that
the mass/light ratio of the spheroid is greater than
that for the disk (they suggest values of 5 and 12, respectively). Also,
the mass distribution of disk stars has a large contribution
from the more massive stars, which are not present in the halo.
Taking all these things into account is tricky, and the best I can do is
to suggest that the disk population probably wins, but not by a large
factor (less than 10).
I hope this helps!
Tim Kallman
for the Ask an Astrophysicist Team
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