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.


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