Data from the CHIME radio observatory are a milestone in the quest to discover the hidden origins of universal structure
Peer into the sky through a powerful telescope, and beyond the glare of the Milky Way, you can make out the faint glow of distant galaxies. These galaxies clump together in dense clusters joined by wispy filaments and separated by enormous voids hundreds of millions of light-years across. Since the 1980s, scientists have observed millions of galaxies to map this “cosmic web” in ever greater detail in their quest to understand our universe’s history.
Uncharted Space In the universe’s “dark ages,” the few hundred million years after protons and electrons first combined to form atoms following the big bang, no stars existed to illuminate all the hydrogen gas then suffusing space. That gas grew denser in some places and more rarefied in others as the tug of gravity competed with cosmic expansion, and the densest regions eventually gave birth to luminous stars, galaxies and galaxy clusters.
The most recent completed galaxy survey, called the Extended Baryon Oscillation Spectroscopic Survey , cataloged the positions and redshifts of half a million galaxies and as many quasars—extremely bright regions at the cores of large galaxies powered by supermassive black holes. The eBOSS team then used this catalog to construct a map that covers about 15 percent of the sky and stretches back more than 11 billion years. And even more ambitious follow-up surveys are underway.
Intensity mapping faces its own challenges. The main difficulty is that the cosmological signal is small, and the Milky Way itself is a strong radio emitter. “You’re trying to look behind it at something which is 1,000 or 10,000 times fainter,” Moodley says. Teasing out the imprint of the cosmic web requires precise telescope modeling and careful analysis.
France Dernières Nouvelles, France Actualités
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