Galaxies organize themselves in large and often dense groups called clusters. These structures are not only interesting for their size, but also because they allow us to understand how the entire universe has evolved through the ages.
For this reason, scientists launched Frontier Fields, a project to take long observations of six galaxy clusters using the Hubble Space Telescope. These observations are combined with other telescopes to produce the most advanced views of these giants we have ever seen.
In the latest images released by NASA, we get a multi-wavelength look at two of these Frontier Fields clusters: MACS J0416.1-2403 and MACS J0717.5+3745 (MACS J0416 and MACS J0717 for short). The images use Hubble in the optical wavelength, Chandra images for the X-ray emission (blue), and the National Science Foundation's (NSF) Jansky Very Large Array (pink). The images show how active these clusters are merging, interacting, and inundating the intergalactic space with hot gas.
MACS J0416 is actually two interacting clusters about 4.3 billion light-years from us. It has been in the eye of astronomers for a long time, because it wasn’t clear if the clusters were about to merge or had already merged. Until now.
Thanks to the combined data, published in the Astrophysical Journal, scientists were able to confirm that the two clusters have been caught before the interaction. They saw that the X-ray emission, which traces the intergalactic hot gas, lines up well with the cluster's mass distribution, and they are yet to separate like what happens during interactions.
MACS J0717 is the largest known gravitational lens. Its mass is spread out over such a large area of the sky that it is capable of distorting space-time and magnifying objects further away from it. The cluster magnified a record of seven radio sources, which is the highest number ever observed in a cluster.
But this is not the only characteristic going for it. The cluster looks messier and more active than MACS J0416, with the large radio arcs evidence of shock waves induced by multiple collisions.
The Frontier Fields program has produced incredible results and more is yet to come. In 2018, NASA and ESA will launch the more powerful James Webb Space Telescope, which will push that frontier even further, all the way to the first galaxies.