Universe’s largest structure caught in the act of forming
“The Universe forms a vast cosmic web where filaments interconnect, with matter flowing along them into a nexus. At the centers of these intersections, the most massive galaxy clusters form. Over time, more clusters fall in, creating the largest structures of all. The Hubble Space Telescope recently observed one of them, MACS J0717, revealing four separate clusters in the collision process.”
When it comes to the largest bound cosmic structures, it doesn’t get any bigger than galaxy clusters. Unless, that it, you consider when multiple galaxy clusters merge together. Located at the intersections of cosmic dark matter filaments, smaller clusters flow into the larger clusters located at such a nexus. When we get very lucky, colliding clusters can be seen. Recently, scientists have located a cosmic smash-up between four such clusters in the large structure MACS J0717.5+3745. One of the clusters within is moving so quickly – 3,000 km/s – that the light within it gets shifted thanks to the speed of the electrons within it. X-ray, radio and optical/IR data combine to reveal a treasure trove of information, including active galaxies, a separation between normal and dark matter and even information about the inflows along the cosmic filaments.