The Cosmic Web
Observations and simulations of the intergalactic medium reveal the largest structures in the universe
The biggest piece of real estate in the universe is the wide-open space between the galaxies, the intergalactic medium. It's about as empty as any place could be—only one lonely atom per cubic meter—but the intergalactic medium has had a long history of interacting with galaxies in interesting ways. Over cosmic time, the galaxies and intergalactic gas have assembled into a vast, three-dimensional "cosmic web" that defines the large-scale structure of the universe. Astronomer Robert Simcoe describes how this structure evolved and how its nature has been revealed through scientific advances in the past decade.
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