Chandra Release - February 14, 2019 Visual Description: H1821+643 The main part of this graphic is from the Millenium simulation, which uses supercomputers to formulate how the key components of the Universe would have evolved over cosmic time. The visualization features pink and purple galaxy clusters, which can be seen as collections of bright spots in the image. These bright spots are connected by a network of lines, creating an intricate structure that resembles a spider's web. An inset at lower left plots X-ray counts vs wavelength over the simulation. Scientists have proposed that missing mass could be hidden in gigantic strands or filaments of warm (temperature less than 100,000 Kelvin) and hot (temperature greater than 100,000 K) gas in intergalactic space. These filaments are known by astronomers as the "warm-hot intergalactic medium" or WHIM. They are invisible to optical light telescopes, but some of the warm gas in filaments has been detected in higher-energy radiation. If these WHIM filaments exist, they could absorb certain types of light such as X-rays that pass through them. The inset in this graphic represents some of the X-ray data collected by Chandra from a distant, rapidly-growing supermassive black hole known as a quasar. The plot is a spectrum - the amount of X-rays over a range of wavelengths - from a study of the quasar H1821+643 that is located about 3.4 billion light years from Earth.