Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

I was reading Wikipedia article about universe and stumbled upon pie chart which represents what universe contains. It says that stars make up 0.5% of whole universe.

I tried to find average distance between stars in the universe, but came to some different numbers, but either way distance is more than 1 light year. At the same time even largest stars in the universe which have 1400 sun radius are 0.00020584 light years in diameter (by my calculations), so it makes absolutely no sense that 0.5% of universe consists of stars, number should be many times smaller. What I am missing here?

share|improve this question
1  
Mistaken, but nice question.. –  Sachin Shekhar Feb 20 at 12:02
1  
Check out what-if.xkcd.com/83 for a great demo. –  Carl Witthoft Feb 20 at 12:36
    
+1 for thinking about what you are reading. –  Ross Millikan Feb 20 at 22:46
add comment

1 Answer 1

up vote 22 down vote accepted

The Wikipedia diagram is giving the breakdown by mass not by volume. Baryonic/leptonic (i.e. non-dark) matter is only about 5% of all matter and of that four fifths of it is in the form of free hydrogen and helium. Of the remaining 1% about half is neutrinos or heavy elements. That means only 0.5% of the mass/energy in the universe is in stars.

share|improve this answer
    
Ahh how I didn't think about that! Thank you John. –  user1880405 Feb 20 at 11:14
3  
...and thus the (in)famous signature line of an early usenet regular,"This universe was packed by weight, not by volume. Some settling of contents may have occurred." –  Carl Witthoft Feb 20 at 12:37
7  
@LoganM Astrophysicists (and, in particular, cosmologists) are a bit looser with their terminology than other physicists. "Baryonic matter" in the astrophysical sense refers to "all matter that isn't dark matter" including - bizarre as it sounds - leptons. If you dislike this, just ask your nearest astronomer friend what they mean by "metal"... –  user27578 Feb 21 at 8:11
1  
@dgh: To be fair, H & He make up around 99% of the elemental matter (meaning common chemical elements), so calling everything that isn't one of those as "metals" makes perfect sense :D –  Kyle Kanos Feb 21 at 18:55
1  
@KyleKanos The critical question here is "Does anyone want to be fair to astrophysicists?". –  dmckee Feb 21 at 19:38
show 3 more comments

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.