Missing Matter Found, But Doesn’t Dent Dark Matter
“But this doesn’t eliminate the need for dark matter; it doesn’t touch that undiscovered 27% of matter in the Universe, not in the slightest. It’s another piece of that 5% that we know is out there, that we’re struggling to put together. It’s just protons, neutrons, and electrons, existing in about six times the abundance within these filaments as compared to the cosmic average. The fact that this filamentary structure contains normal matter at all is further evidence for dark matter, since without it there’d be no gravitationally overdense regions to hold the extra normal matter in place. In this case, the WHIM traces the dark matter, further confirming what we know must be out there.”
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. 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.