Caltech astronomers have taken unprecedented images of the intergalactic medium (IGM) -- the diffuse gas that connects galaxies throughout the universe -- with the Cosmic Web Imager, an instrument designed and built at Caltech. Until now, the structure of the IGM has mostly been a matter for theoretical speculation. However, with observations from the Cosmic Web Imager, deployed on the Hale 200-inch telescope at Palomar Observatory, astronomers are obtaining our first three-dimensional pictures of the IGM. The Cosmic Web Imager will make possible a new understanding of galactic and intergalactic dynamics, and it has already detected one possible spiral-galaxy-in-the-making that is three times the size of our Milky Way.

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Since the late 1980s and early 1990s, theoreticians have predicted that primordial gas from the Big Bang is not spread uniformly throughout space, but is instead distributed in channels that span galaxies and flow between them. This "cosmic web" -- the IGM -- is a network of smaller and larger filaments crisscrossing one another across the vastness of space and back through time to an era when galaxies were first forming and stars were being produced at a rapid rate.