Illustration of Sculptor Wall (with Spectrum of H2356-309): At a distance of about 400 million light years from Earth, a massive “wall” of galaxies stretching tens of millions of light years.
Caption: This artist’s illustration shows a close-up view of the Sculptor Wall, which is comprised of galaxies along with the warm-hot intergalactic medium (WHIM). Scientists used Chandra and XMM-Newton to detect the WHIM in this structure by examining the X-ray light from a distant quasar, which is represented in the inset to the upper right. This discovery is the strongest evidence yet that the "missing matter" in the nearby Universe is located in an enormous web of hot, diffuse gas.
Chandra X-ray Observatory