This part of space may look like nothing special, but it's actually home to a tightly packed "galaxy city," composed of thirty extremely ancient galaxies. It's a big find... and it took thousands of hours of observation before anyone noticed.
Located 10.5 billion light-years away, this galaxy cluster is the most distant — and, consequently, the oldest — known example of a red galaxy cluster. That red color gives us vital clues about the mass and configuration of the galaxies in question, and we're most likely looking at elliptical galaxies. We're catching this cluster at a very early stage in its development — its discoverers at the Carnegie Observatories say it could evolve to a giant, dense cluster of over a thousand galaxies.
This area of space has been under constant observation by a number of telescopes, including Hubble, and yet nobody had turned up any evidence that the galaxy cluster was there. That's because this cluster is extremely faint and essentially invisible in all but a very narrow slice of the infrared spectrum.
The astronomers were able to detect the cluster using the new FourStar camera on the Magellan Baade Telescope, which they used to provide extremely accurate measurements of the distances between Earth and thousands of different galaxies, which they in turn used to build up a 3D map of this area of the universe. The astronomers used this data to spot a strangely high concentration of galaxies at this particular point in space and time, revealing the existence of this cluster.
Via the Carnegie Institution.