A Hole in the Cosmic Microwave Background


The Cosmic Microwave Background (CMB) in the afterglow of the Big Bang. Why would this cluster of galaxies punch a hole in it? The CMB flows right through most of the gas and dust in the universe. It is all around us. However, large clusters of galaxies have enough gravity to contain gas hot enough to up-scatter the CMB photons into light of significantly higher energy, creating “holes” in the CMB. This is known as the Sunyaev–Zel’dovich (SZ) effect, and it’s used for decades to study the hot gas in clusters. This picture combines CMB data from ESO’s ALMA with imagery from the Hubble Space Telescope to measure the galaxies in the massive galaxy cluster RX J1347.5-1145. False-color blue shows light from the CMB; almost every yellow object is a galaxy. The shape of the SZ hole indicates not only that hot gas is present in this galaxy cluster, but also that it is distributed in a surprisingly uneven manner.

Image Credit: ESO / ESA / NASA

Mergers and Acquisitions


A cosmic kaleidoscopeThis multi-colored haze is actually two colliding galaxy clusters that are forming a single object known as MACS J0416.1-2403 (or MACS J0416 for short). It’s located about 4.3 billion light-years from Earth. This image combines data from three different telescopes: the Hubble Space Telescope (showing the galaxies and stars), the Chandra X-ray Observatory (diffuse emission in blue), and the NRAO Very Large Array (diffuse emission in pink). Each telescope shows a different element of the cluster.

As with all galaxy clusters, MACS J0416 contains a significant amount of dark matter which leaves a detectable imprint in visible light by distorting the images of background galaxies. In this image the dark matter appears to align well with the blue-hued hot gas, suggesting that the two clusters have not yet collided. If the clusters had already merged, the dark matter and gas would have separated.

Image credit: NASA / ESA / CXC / NRAO-AUI-NSF /STScI / G. Ogrean (Stanford University)