The map was created by using faint background galaxies as light sources, against which gas could be seen by the characteristic absorption features of hydrogen. (keckobservatory.org)
Their absorption measurements using 24 faint background galaxies provided sufficient coverage of a small patch of the sky to be combined into a 3D map of the foreground cosmic web. (keckobservatory.org)
Using the light from faint background galaxies for this purpose had been thought impossible with current telescopes — until Lee carried out calculations that suggested otherwise. (keckobservatory.org)