Exploring the Intergalactic Medium
A Cosmic Web Imager view of a distant quasar. The blue denotes hydrogen gas surrounding and flowing into the quasar in the early universe.
It may seem like an easy question to answer: what is there out between the galaxies? The answer is NOT "an empty vacuum", thanks to a series of images taken with a specialized instrument called the Cosmic Web Imager built by the California Institute of Technology (CalTech). It is being used at Palomar Observatory on the 200-inch Hale telescope to look between galaxies and measure the thin mix of gases that astronomers now know exists there. They call it "dim matter" because it isn't bright like stars or nebulae, but it's not so dark it can't be detected. The Cosmic Web Imager looks for this matter in the intergalactic medium (IGM) and finds it. How does it do this?...Read Full Post