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Distant quasar shows up gross error in standard cosmological model

20 January 2013

Astronomers have discovered a distant quasar illuminating a vast nebula of diffuse gas, containing far more normal matter than predicted by the current cosmological model. Researchers at the University of California led the study, published in Nature.

Using the 10-meter Keck I Telescope at the WM Keck Observatory in Hawaii, the researchers detected a very large, luminous nebula of gas extending about 2 million light-years across intergalactic space.

"This is a very exceptional object: it's huge, at least twice as large as any nebula detected before, and it extends well beyond the galactic environment of the quasar," said first author Sebastiano Cantalupo.

The standard cosmological model of structure formation in the universe predicts that galaxies are embedded in a cosmic web of matter, most of which (about 84 percent) is invisible dark matter. This web is seen in computer simulations of the evolution of the universe.

These simulated maps show the predicted distribution of dark matter on large scales, including the dark matter halos in which galaxies are supposed to form, and the cosmic web of filaments that would connect them.

It is thought that gravity would cause ordinary matter to follow the distribution of dark matter; so filaments of diffuse, ionized gas are expected to trace a pattern similar to that seen in the dark matter simulations.

Until now, however, these filaments have never been seen. Intergalactic gas has been detected by its absorption of light from bright background sources, but those results don't reveal how the gas is distributed. In this study, the researchers detected the fluorescent glow of hydrogen gas resulting from its illumination by intense radiation from the quasar.

This computer simulation of the large-scale structure of supposed dark
matter plus normal gas in the universe (Bolshoi simulation, by Anatoly
Klypin and Joel Primack) predicts less than one tenth of the gas that
was actually observed by the Keck I Telescope.

"This quasar is illuminating diffuse gas on scales well beyond any we've seen before, giving us the first picture of extended gas between galaxies. It provides a terrific insight into the overall structure of our universe," said co-author J. Xavier Prochaska.

The researchers estimated the amount of gas in the nebula to be at least ten times more than expected from the results of computer simulations. "These observations are challenging our understanding," Cantalupo said.

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