http://www.sciencemag.org/news/2017/10/ ... sing-atoms
Astronomers say they’ve found many of the universe’s missing atoms
If you get frustrated when you can't find your keys, imagine how astronomers feel. For years they’ve been unable to locate roughly half the atoms they think the universe must contain. Now, researchers have tracked down a lot of that missing matter using radiation from the early universe that acts a bit like a laser illuminating billowing smoke. The finding helps solidify our understanding of how the universe has evolved over time.
Cosmologists know roughly how much hydrogen and helium was created during the first 20 minutes after the big bang. These numbers are corroborated by studies of the afterglow of the big bang—the so-called cosmic microwave background (CMB)—which suggests that our universe is made of roughly 70% dark energy, 23% dark matter, and only 4.6% of ordinary, or baryonic, matter. However, stars and galaxies account for only about 10% of the inferred ordinary matter, and all told researchers cannot account for up to half of atoms they think should exist.
“This is embarrassing, as you can imagine,” says astronomer Renyue Cen of Princeton University, who was not involved in the new work. “Not only do we have most of matter which is dark, and most of energy which is still darker; but of the 5% which is normal atoms, most are missing.”
Researchers think they know where the baryons are. According to the standard cosmological model, which predicts how the universe has grown and changed since its earliest days, the universe is filled with enormous strands of dark matter, and the galaxies are embedded in this so-called cosmic web. Scientists hypothesize that the missing atoms lie in diffuse clouds of highly ionized gas stretching between the galaxies. Known as warm-hot intergalactic matter (WHIM), that million-degree gas glows in x-rays, but is so thin it’s very hard to see. Using observatories that can see ultraviolet radiation, like the Hubble Space Telescope, astronomers have spotted enough WHIM to account for about 50% to 70% of the missing baryons—still leaving a significant fraction unaccounted for.
• A Search for Warm/Hot Gas Filaments Between Pairs of SDSS Luminous Red Galaxieshttps://www.newscientist.com/article/21 ... lly-found/
Two separate teams found the missing matter – made of particles called baryons rather than dark matter – linking galaxies together through filaments of hot, diffuse gas
“The missing baryon problem is solved,” says Hideki Tanimura at the Institute of Space Astrophysics in Orsay, France, leader of one of the groups. The other team was led by Anna de Graaff at the University of Edinburgh, UK.
Hideki Tanimura, Gary Hinshaw et al https://arxiv.org/abs/1709.05024
• Missing baryons in the cosmic web revealed by the Sunyaev-Zel'dovich effect
Anna de Graaff, Yan-Chuan Cai et al https://arxiv.org/abs/1709.10378