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Wednesday, May 7, 2008

XMM-Newton Discovers Part of Missing Universe

ESA’s orbiting X-ray observatory XMM-Newton has been used by a team of international astronomers to uncover part of the missing matter in the universe.

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10 years ago, scientists predicted that about half of the missing ‘ordinary’ or normal matter made of atoms exists in the form of low-density gas, filling vast spaces between galaxies.

All the matter in the universe is distributed in a web-like structure. At dense nodes of the cosmic web are clusters of galaxies, the largest objects in the universe. Astronomers suspected that the low-density gas permeates the filaments of the web.

The low density of the gas hampered many attempts to detect it in the past. With XMM-Newton’s high sensitivity, astronomers have discovered its hottest parts. The discovery will help them understand the evolution of the cosmic web.


Only about 5% of our universe is made of normal matter as we know it, consisting of protons and neutrons, or baryons, which along with electrons, form the building blocks of ordinary matter. The rest of our universe is composed of elusive dark matter (23%) and dark energy (72%).


Small as the percentage might be, half of the ordinary baryonic matter is unaccounted for. All the stars, galaxies and gas observable in the universe account for less than a half of all the baryons that should be around.


Astronomers using XMM-Newton were observing a pair of galaxy clusters, Abell 222 and Abell 223, situated at a distance of 2300 million light-years from Earth, when the images and spectra of the system revealed a bridge of hot gas connecting the clusters.