This deep image shows the region of the sky around the quasar HE0109-3518. The quasar is labeled with a red circle near the center of the image. The energetic radiation of the quasar makes dark galaxies glow, helping astronomers to understand the obscure early stages of galaxy formation. The faint images of the glow from 12 dark galaxies are labeled with blue circles. Dark galaxies are essentially devoid of stars, therefore they don’t emit any light that telescopes can catch. This makes them virtually impossible to observe unless they are illuminated by an external light source like a background quasar.
This image combines observations from the Very Large Telescope, tuned to detect the fluorescent emissions produced by the quasar illuminating the dark galaxies, with color data from the Digitized Sky Survey 2.
Photo credit: ESO, Digitized Sky Survey 2 and S. Cantalupo (UCSC)
Note: For more information, see Dark Galaxies of the Early Universe Spotted for the First Time. An unannotated version of this image may be found here.