“On a cosmic scale, our life is insignificant, yet this brief period when we appear in the world is the time in which all meaningful questions arise.” -Paul Ricoeur
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.
The combination of radio and X-ray data reveal background, lensed galaxies and signatures of active black holes within the colliding cluster. Image credit: X-ray: NASA/CXC/SAO/G.Ogrean et al.; Optical: NASA/STScI; Radio: NRAO/AUI/NSF.
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.
Hubble Space Telescope optical image (green), mass map (Limousin et al 2012; contours), and CSO/Bolocam 140 GHz (red) and 268 GHz (blue) maps of the galaxy cluster MACS J0717+3745. The lack of 268 GHz signal at subcluster B (second large concentration from upper right) is due to the kinetic Sunyaev-Zeldovich effect. Image credit: P. Korngut.