May 7, 2008 -- An orbital X-ray telescope has found a chunk of matter whose existence had long been theorized, but evidence for which had been lacking, the European Space Agency (ESA) said on Wednesday.
The discovery made by ESA's XMM-Newton telescope is part of so-called baryonic matter, which comprises less than five percent of the cosmos.
Most of the universe consists of matter and energy of an unknown nature, which astrophysicists call "dark matter." It is believed to be distributed in a web-like structure.
"Dark energy," which causes an accelerated expansion of the universe after the Big Bang that created it, accounts for some 72 percent of the total, and "dark matter" -- heavy particles still waiting to be discovered -- accounts for around 23 percent, according to this theory.
That leaves just 4.6 percent to comprise normal, or baryonic, matter, the category including ordinary particles such as protons and neutrons.
But only a small fraction of this stuff has been found. All the stars, galaxies and gas observed in the universe account for less than half of the baryonic matter that should be there.
The new claim is based on the observation of a pair of distant galaxy clusters, called Abell 222 and Abell 223, located 2.3 billion light-years from Earth.
Images and spectra found that the two clusters were linked by a bridge of hot, ultra-low-density gas.
The astronomers believe that such gas permeates the filaments of the cosmic web around the universe.
"The hot gas that we see in this bridge or filament is probably the hottest and densest part of the diffuse gas in the cosmic web, which is believed to constitute about half of the baryonic matter in the universe," said lead researcher Norbert Werner of the SRON Netherlands Institute for Space Research.
"This is only the beginning," he said.
"To understand the distribution of the matter within the cosmic web, we have to see many more systems like this -- and ultimately launch a dedicated space research laboratory with a much higher sensitivity than possible with the current satellites."
The research has been published by the journal Astronomy and Astrophysics Letters, ESA said in a press release.
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