Starts With A Bang

Missing Matter Found, But Doesn’t Dent Dark Matter (Synopsis)

A nearly uniform Universe, expanding over time and under the influence of gravity, will create a cosmic web of structure. The web contains both dark and normal matter. Image credit: Western Washington University.

“There are stars leaving the Milky Way, and immense gas clouds falling into it. There are turbulent plasmas writhing with X- and gamma-rays and mighty stellar explosions. There are, perhaps, places which are outside our universe. The universe is vast and awesome, and for the first time we are becoming a part of it.” -Carl Sagan

It’s no secret that if we look at the matter we see in the Universe, the story doesn’t add up. On all scales, from individual galaxies to pairs, groups and clusters of galaxies, all the way up to the large-scale structure of the Universe, the matter we see is insufficient to explain the structures we get. There has to be more matter, both normal (atom-based) matter and dark (non-interacting) matter, to make our theory and predictions match.

Constraints on dark energy from three independent sources: supernovae, the CMB and BAO. Note that even without supernovae, we’d need dark energy, and that only 1/6th of the matter found can be normal matter; the rest must be dark matter. Image credit: Amanullah, et al., Ap. J. (2010).

In a wonderful new pair of papers, two independent teams have detected the warm-hot intergalactic medium along the large-scale structure filaments in the Universe. With six times the normal matter density, this accounts for a significant fraction of the missing normal matter in the Universe! It’s estimated that 50-90% of the baryons in the Universe are part of the WHIM, and this could be the first step towards detecting them. But it doesn’t touch or change the dark matter at all; we still need it and still don’t have it.

The warm-hot intergalactic medium (WHIM) has been seen before, but only along incredibly overdense regions, like the Sculptor wall, illustrated above. Image credit: Spectrum: NASA/CXC/Univ. of California Irvine/T. Fang. Illustration: CXC/M. Weiss.

What’s the full story on the discovery of the missing matter? Find out over at Starts With A Bang on Forbes!