This collage shows images of six different galactic clusters made with the NASA Hubble Space Telescope. Clusters were discovered during attempts to investigate the behavior of dark matter in galactic clusters when they collide. In total, scientists have studied 72 large cluster collisions. Using images with visible light, made with the help of Hubble, the scientists saw the map of the distribution of stars after the collision, as well as the location of the dark matter (colored blue).
The results of observations made with the help of two powerful space telescopes turned out to be as follows: dark matter occupying the minds of the entire scientific community, constituting about 85% of the total volume of matter in the Universe, is even stranger than was previously thought.
New research has enabled scientists to find out how dark matter interacts with itself over time. A study published March 27 in the journal Science presents a kind of chronology. Using a series of cluster collisions, scientists were able to show how the clouds of dark matter contained in these clusters interact. According to David Harvey, one of the study leaders at the Swiss Federal Polytechnic School of Lausanne, observing dark matter during such “cosmic accidents” will allow scientists to get a more concrete idea of what it really is. When two galactic clusters collide, the stars, gas, and dark matter interact in different ways. Clouds of gas overcome resistance, slow down and often even stop, then, as the stars fly past each other (sometimes they may collide, but this happens very rarely). Studying what happens at this time with dark matter, the researchers realized that, like stars, dark matter clouds have only a small effect on each other.
It is logical to assume that if dark matter clouds were evenly distributed in each cluster, then at collision they, like gas clouds, would very strongly interact and enter into direct contact. However, they slide into each other smoothly, instead of experiencing resistance. However, as co-author Richard Massey of the University of Durham notes, each collision of clusters takes several hundred million years. Therefore, a person can see only a still image from a single angle. And only the study of a large number of collisions allows you to more or less accurately put together the entire “movie”. So, having determined that dark matter particles do not experience strong friction, being in close proximity to particles of another dark matter cloud, scientists want to find out if these particles repel each other, like billiard balls. Such a kinetic interaction could explain the dark matter property dispersed in huge galactic collisions. Also, researchers want to observe the behavior of dark matter in collisions of single galaxies, which occurs much more often than collisions of galactic clusters.