The return of the ordinary missing mass

In recent years, astronomers have come to know better the composition of our Universe: 70% dark energy, 25% dark matter (both equally mysterious) and about 5% of ordinary matter.

According to the standard cosmological model, the total number of elementary particles that form this ordinary matter (baryons like protons and neutrons) has remained constant since
Big Bang. But the baryons detected in our near universe are half as numerous as those of the Big Bang universe. To account for the missing half, the theory therefore predicts the existence of what is called WHIM (Warm-Hot Intergalactic Medium), an intergalactic web of hot and diffuse gases. Continuing work published two years ago by four teams of astronomers, Fabrizio Nicastro of the Harvard-Smithsonian Center for Astrophysics and his colleagues studied the absorption spectrum of the quasar Markarian 421, based on Observatory data. X-ray Chandra and observations of emissions in the ultraviolet. they have
thus discovered the presence of ions (carbon, nitrogen, oxygen and neon) in two gas clouds heated to nearly one million degrees Celsius traversed by the quasar. By extrapolating to the whole Universe the size of these WHIM representatives located at 150 and 370 million light-years from Earth, scientists were able to accurately estimate the density of baryons contained in this type of environment. .

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And this estimate corresponds to the missing mass. New instruments will undoubtedly be needed to finalize this research. It was planned to install a spectrograph on Hubble
but the uncertain future of the telescope now compromises this project.

NYT 08 / 02 / 05 (Recovering lost atoms of cosmos)
http://www.nytimes.com/2005/02/08/science/space/08mass.html
http://chandra.harvard.edu/press/05_releases/press_020205.html
http://web.mit.edu/newsoffice/2002/hotgas-0814.html

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