* Astronomy

X-ray Discovery Points to Location of Missing Matter

Using observations with NASA's Chandra X-ray Observatory and ESA's XMM-Newton, astronomers have announced a robust detection of a vast reservoir of intergalactic gas about 400 million light years from Earth. This discovery is the strongest evidence yet that the "missing matter" in the nearby Universe is located in an enormous web of hot, diffuse gas.
This missing matter -- which is different from dark matter -- is composed of baryons, the particles, such as protons and electrons, that are found on the Earth, in stars, gas, galaxies, and so on. A variety of measurements of distant gas clouds and galaxies have provided a good estimate of the amount of this "normal matter" present when the universe was only a few billion years old. However, an inventory of the much older, nearby universe has turned up only about half as much normal matter, an embarrassingly large shortfall.
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Although the universe contains billions of galaxies, only a small amount of its matter is locked up in these behemoths. Most of the universe's matter that was cooked up during and just after the Big Bang must be found elsewhere.
Now, in an extensive search of the relatively recent, local universe, University of Colorado at Boulder astronomers said they have definitively found about half of the missing normal matter, called baryons, in the spaces between the galaxies. This important component of the universe is known as the intergalactic medium and it extends essentially throughout all of space, from just outside our Milky Way galaxy to the most distant regions of space observed by astronomers.

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Astronomers detect a part of long-searched baryonic matter in a filament connecting two clusters of galaxies
The composition of the Universe still puzzles the astronomers: Over 90 percent consist of unknown matter - three quarters of the mysterious Dark Energy which causes an accelerated expansion of the Universe and about 21 percent of Dark Matter, the components of which the physicists have not yet figured out. Just four percent are composed of the normal material of which we ourselves are made, the so-called baryonic matter. Even this minor part however has not yet been comprehended completely: all discovered stars, galaxies and gases in the Universe amount to less than a half of these four percent. Now a team of astrophysicists from the Max Planck Institute for extraterrestrial Physics (MPE) and the ESO, both in Garching, Germany, and of two institutes in the Netherlands has found evidence of a part of the missing baryons in a bridge-like filament connecting two clusters of galaxies (Astronomy & Astrophysics Letters, May 2008).

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