Mass of universe

[jimjohnson]

In the Augest issue of Astronomy on page 57, it says the contents of universe is: 70% dark energy; 25% dark matter; 4% free hydrogen and helium; .5% stars; and .5% for everything else.
Is the 4% correct? I thought intersteller matter (free hydrogen/helium) was only about 10% of the physical mass and stars 90%.

[mathman]

From what I've read, stars constitute about 10% of baryonic matter. The information you have looks correct.

[bcrowell]

Isn't there an extremely wide range of uncertainty on the ratio of baryonic matter in stars to baryonic matter not in stars?

[jimjohnson]

Wikipedia says that half of the ISM is in molecular cloulds and in the Milky Way there are 6,000 cloulds each with 100,000 solar masses. Thus, the mass would be: 6 x 2 x e8 or 1.2 x e9 solar masses. This might be 1% of the mass of the e11 solar masses in the Milky Way (concervative estimate). Thus, I think the Astronomy article should say 4% stars not .5%.

[bcrowell]

Wikipedia says that half of the ISM is in molecular cloulds and in the Milky Way there are 6,000 cloulds each with 100,000 solar masses. Thus, the mass would be: 6 x 2 x e8 or 1.2 x e9 solar masses. This might be 1% of the mass of the e11 solar masses in the Milky Way (concervative estimate). Thus, I think the Astronomy article should say 4% stars not .5%.

That doesn't address the question of what the error bars are on all these numbers. Wouldn't surprise me at all if there were error bars amounting to a factor of 10.