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?


1 Answer 1


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.

  • $\begingroup$ Ahh how I didn't think about that! Thank you John. $\endgroup$ Feb 20, 2014 at 11:14
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    $\begingroup$ ...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." $\endgroup$ Feb 20, 2014 at 12:37
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    $\begingroup$ @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"... $\endgroup$
    – user27578
    Feb 21, 2014 at 8:11
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    $\begingroup$ @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 $\endgroup$
    – Kyle Kanos
    Feb 21, 2014 at 18:55
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    $\begingroup$ @KyleKanos The critical question here is "Does anyone want to be fair to astrophysicists?". $\endgroup$ Feb 21, 2014 at 19:38

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