Universe's 'missing matter' discovered

Astronomers have uncovered part of the missing matter in the universe, a discovery which they claim will help in understanding the evolution of the cosmic web in the future.

Ten years ago, scientists predicted about half of the missing "ordinary" or normal matter made up of atoms exists in the form of a low density gas, filling the vast spaces between galaxies. But attempts to detect it in the past were hampered.
 
Now, an international team has discovered its hottest parts using the European Space Agency's orbiting observatory, the XMM-Newton.

They were observing a pair of galaxy clusters – Abell 222 and Abell 223 -- situated at a distance of 2,300 million light years from Earth, when images and spectra of the system revealed a bridge of hot gas connecting them, the ESA said.

"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, believed to constitute about half the baryonic matter in the universe," said team leader Norbert Werner of  Netherlands Institute for Space Research 
 
Added team member Alexis Finoguenov: "The discovery of the warmest of the missing baryons is important. That's because various models exist and they all predict that the missing baryons are some form of warm gas, but the models tend to disagree about the extremes."

Even with XMM-Newton's sensitivity, the discovery was only possible because the filament is along the line of sight, concentrating the emission from the entire filament in a small region of the sky, according to the astronomers.

"This is only the beginning. To understand the distribution of the matter within the cosmic web, we have to see more systems like this one. And ultimately launch a dedicated space observatory to observe the cosmic web with a much higher sensitivity than possible with current missions. Our result allows to set up reliable requirements for those new missions," Werner said.

ESA's XMM-Newton project scientist, Norbert Schartel, comments on the discovery: "This important breakthrough is great news for the mission. The gas has been detected after hard work and more importantly, we now know where to look for it. I expect many follow-up studies with XMM-Newton in the future targeting such highly promising regions in the sky."