macs j0717.5 3745


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.

This may be the messiest galaxy cluster ever found, but it’s also the most instrumental in understanding the formation of the Universe’s largest structures. Catch it on today’s Mostly Mute Monday!


Hubble image of MACS J0717 with mass overlay

This enormous image shows Hubble’s view of massive galaxy cluster MACS J0717.5+3745. The large field of view is a combination of 18 separate Hubble images.

Studying the distorting effects of gravity on light from background galaxies, a team of astronomers has uncovered the presence of a filament of dark matter extending from the core of the cluster.

The location of the dark matter is revealed in a map of the mass in the cluster and surrounding region, shown here in blue. The filament visibly extends out and to the bottom of the cluster core.

Using additional observations from ground-based telescopes, the team was able to map the filament’s structure in three dimensions, the first time this has ever been done. The filament was discovered to extend back from the cluster core, meaning we are looking along it.

Credit: NASA, ESA, Harald Ebeling (University of Hawaii at Manoa) & Jean-Paul Kneib (LAM)