This optical image of the newfound galaxy cluster highlights how faint and reddened these galaxies are due to their great distance. The cluster remained hidden until the South Pole Telescope spotted it by looking for distortions in the cosmic microwave background. (Such distortions are called the Sunyaev-Zel'dovich effect.) The blue streak is a satellite passing through the field of view during the timed exposure. Credit: CTIO Blanco 4-m telescope/J. Mohr (LMU Munich)
Galaxy clusters like this can be used to study how dark matter and dark energy influenced the growth of cosmic structures. Long ago, the universe was smaller and more compact, so gravity had a greater influence. It was easier for galaxy clusters to grow, especially in areas that already were denser than their surroundings.
"You could say that the rich get richer, and the dense get denser," quipped Harvard astronomer Robert Kirshner, commenting on the study.
As the universe expanded at an accelerating rate due to dark energy, it grew more diffuse. Dark energy now dominates over the pull of gravity and chokes off the formation of new galaxy clusters.
Brodwin and his colleagues spotted their quarry in the first 200 square degrees of data collected from the new South Pole Telescope. The SPT is currently completing its pioneering millimeter-wave survey of a huge swath of sky covering 2,500 square degrees.
They're hunting for giant galaxy clusters using the Sunyaev-Zel'dovich effect - a small distortion of the cosmic microwave background (a pervasive all-sky glow left over from the Big Bang). Such distortions are created as background radiation passes through a large galaxy cluster.