 |
| Composite image of the massive galaxy cluster MACS J0717.5+3745 from NASA's Chandra X-ray Observatory. Image size is roughly 7.7 million light years across. |
MACS J0717.5+3745 (MACS J0717 or MACS 0717 for short) is a large galaxy cluster located 5.4 billion light years away in the constellation Auriga,appearing in the MAssive Cluster Survey (MACS).
The cluster was formed by four separate galaxy clusters that have been involved in a collision. This is the first time that this phenomenon has been observed. The repeated collisions in MACSJ0717 are caused by a 13-million-light-year-long stream of galaxies, gas, and dark matter, known as a filament, pouring into a region already full of matter. When two or more of the galaxy clusters collide, the hot gas in the interstellar medium slows down, but the galaxies, composed mostly of empty space, do not slow as fast. The speed and direction of each of the clusters involved in the collision can thus be approximated through examining the offset between the galaxies and the gas.
 |
| Near-infrared Hubble Space Telescope image of MACS J0717.5+3745. |
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 left 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)