
Observations of the missing baryons in the warm–hot intergalactic medium - devilmoon
https://www.nature.com/articles/s41586-018-0204-1
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biofunsf
Sci-Hub link to the full paper: [https://sci-
hub.tw/https://www.nature.com/articles/s41586-01...](https://sci-
hub.tw/https://www.nature.com/articles/s41586-018-0204-1)

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ChuckMcM
phys org link [https://phys.org/news/2018-06-universe-
ordinary.html](https://phys.org/news/2018-06-universe-ordinary.html) which has
a bit better explanation.

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dwaltrip
The 1/3 missing baryons is composed of oxygen gas?! That is a huge change,
right?

I thought the elemental distribution of the universe is around 90% hydrogen,
8% helium, and 2% all the other elements (going off memory here).

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antognini
No, while the observations were of oxygen, this doesn't imply that the gas is
primarily made of oxygen. The issue with the warm-hot IGM is that it is a
strange temperature where virtually nothing emits much light. Highly ionized
oxygen (in this case, only one electron out of the original eight remain
bound) is one of the few things that does. Here, based on X-ray observations
they have estimated the density of this oxygen, and then estimated the overall
density of the IGM based on the ratio of oxygen to hydrogen.

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wrycoder
Thanks for that explanation. With it, the abstract makes sense regarding the
fully ionized hydrogen. The phys.org article ("That lost matter exists as
filaments of oxygen gas") does not.

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PhantomGremlin
So, since baryons are protons and neutrons, if I understand this, then 40% of
the ordinary matter in the universe can be found outside of galaxies?

Why can't that missing ordinary matter serve the same role as recent beloved
explanation "dark matter" does? Or is it just too diffuse to affect things
like the galaxy rotation curve?

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the8472
I guess (IANAP) that's because hydrogen is easier to observe as part of
interstellar gas within a galaxy as opposed to the thinner intergalactic
filaments which is also further away and doesn't get illuminated by stars or
stellar remnants.

So the baryonic matter in galaxies is already accounted for to a larger extent
than the filaments.

