3 February 2005
On the trail of the missing baryons
According to current cosmological models, baryons — elementary particles found in normal everyday matter — make up about 5% of the total mass density of the Universe. Observations at high redshifts support that prediction, but nearer home in space and time only half as many baryons have been detected. This has prompted a search for missing 'normal' (as opposed to 'dark') matter. Nicastro et al. report the discovery of a previously unknown source of baryons lying in a warm–hot phase of the intergalactic medium — and their mass is consistent with that of the 'missing' baryons.
The mass of the missing baryons in the X-ray forest of the warm-hot intergalactic medium
FABRIZIO NICASTRO, SMITA MATHUR, MARTIN ELVIS, JEREMY DRAKE, TAOTAO FANG, ANTONELLA FRUSCIONE, YAIR KRONGOLD, HERMAN MARSHALL, RIK WILLIAMS & ANDREAS ZEZAS
Nature 433, 495–498 (2005); doi:10.1038/nature03245
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Astronomy: Hot pursuit of missing matter
J. MICHAEL SHULL
Astronomers are going to extraordinary lengths in the quest to tot up the 'ordinary' matter in the Universe. The latest initiative has probed hot gas in intergalactic space by means of an X-ray lighthouse.
Nature 433, 465–466 (2005); doi:10.1038/433465a
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