The Hubble Space Telescope found a ghost ring made of dark matter

The scientists were able to identify the behavior of dark matter during a massive collision between two galaxy clusters. The destruction created ripples of dark matter, reminiscent of ripple behavior in a lake into which a stone has been thrown

The most common substance in the universe is dark matter, it does not shine or reflect light - we cannot see it! It is invisible matter, made of atoms that are completely different from those that make up the atoms in "our" ordinary material universe, of which stars and galaxies are made. So much so that a vehicle that drives directly into a wall made of dark material will suffer no damage at all - no headlights will break and the airbags will not inflate. You will not feel any sign of this. But - what will happen to the dark matter during a collision?

Astronomers have now observed with the Hubble Space Telescope directly the behavior of dark matter during a massive collision between two galaxy clusters. The destruction created ripples of dark matter, reminiscent of ripple behavior in a lake into which a stone has been thrown. The discovery of the ring is one of the most significant pieces of evidence that points to the existence of dark matter. Astronomers have long assumed the existence of dark matter whose mass helps galaxy clusters not to disintegrate, such clusters would disintegrate if they were held only by the gravity of the stars that can be seen. Although it is not known what the dark matter is made of, it is assumed that it is a basic particle that is the most common in the universe.

The ring-like structure that can be seen in the image is a composite of the image of the cluster as taken by the Hubble Space Telescope and a blue mapping of the distribution of the dark matter in that area. The team of astronomers of the Hubble Space Telescope point out that this is the first time that dark matter has a clear structure that differs from the distribution of gas and galaxies in the cluster. The researchers noticed the existence of the ring while mapping the distribution of dark matter around the galaxy cluster Cl 0024+17 (ZwCl 0024+1652) which is about 5 billion light years from Earth. The diameter of the ring is about 2.6 million light years (slightly more than the distance to the Andromeda galaxy).

Although dark matter cannot be observed directly, its existence can be inferred because its gravity causes the light coming from even more distant galaxies to be bent, an impressive effect called gravitational distortion. The blue "bows" that can be seen in another image of the cluster taken by the Hubble Space Telescope are those distant galaxies whose light is bent and concentrated by the strong gravity of the cluster.

The collision between the galaxies left clear traces in the form of the ripples in the dark matter which cause the light from the distant galaxies to be filtered. This is similar to looking at low stones at the bottom of a lake over which waves move - the shape of the stones appears to change when the waves pass over them. So the galaxies behind the dark matter ring also look different. While dark matter has previously been found in other galaxies, the team of astronomers explained that the diffuse dark matter has never been observed so it is unrelated to the gas distribution seen in the galaxy cluster.

The team of researchers found according to a previous study that the cluster is the result of a collision between two very ancient galaxy clusters about one to two billion years ago. The team then performed simulations of a collision between galaxy clusters, according to which it appears that the dark matter is concentrated to the common center of mass of the two clusters and is then splashed outwards. When the dark matter begins its outward movement it is slowed down by gravity and accumulates, similar to a traffic jam on a highway.

For information on the NASA website