In a series of three recent papers, astronomers have identified the final chunks of all the ordinary matter in the universe. From a report: And despite the fact that it took so long to identify it all, researchers spotted it right where they had expected it to be all along: in extensive tendrils of hot gas that span the otherwise empty chasms between galaxies, more properly known as the warm-hot intergalactic medium, or WHIM. Early indications that there might be extensive spans of effectively invisible gas between galaxies came from computer simulations done in 1998. “We wanted to see what was happening to all the gas in the universe,” said Jeremiah Ostriker, a cosmologist at Princeton University who constructed one of those simulations along with his colleague Renyue Cen. The two ran simulations of gas movements in the universe acted on by gravity, light, supernova explosions and all the forces that move matter in space. “We concluded that the gas will accumulate in filaments that should be detectable,” he said. Except they weren’t — not yet. “It was clear from the early days of cosmological simulations that many of the baryons would be in a hot, diffuse form — not in galaxies,” said Ian McCarthy, an astrophysicist at Liverpool John Moores University. Astronomers expected these hot baryons to conform to a cosmic superstructure, one made of invisible dark matter, that spanned the immense voids between galaxies. The gravitational force of the dark matter would pull gas toward it and heat the gas up to millions of degrees. Unfortunately, hot, diffuse gas is extremely difficult to find. To spot the hidden filaments, two independent teams of researchers searched for precise distortions in the CMB, the afterglow of the Big Bang. As that light from the early universe streams across the cosmos, it can be affected by the regions that it’s passing through. In particular, the electrons in hot, ionized gas (such as the WHIM) should interact with photons from the CMB in a way that imparts some additional energy to those photons. The CMB’s spectrum should get distorted. Unfortunately the best maps of the CMB (provided by the Planck satellite) showed no such distortions. Either the gas wasn’t there, or the effect was too subtle to show up. But the two teams of researchers were determined to make them visible. From increasingly detailed computer simulations of the universe, they knew that gas should stretch between massive galaxies like cobwebs across a windowsill. Planck wasn’t able to see the gas between any single pair of galaxies. So the researchers figured out a way to multiply the faint signal by a million.
of this story at Slashdot.
Source:: Slashdot