6.5 million light years: this is the largest shock wave ever observed in the Universe

The South African MeerKAT radio telescope is a precursor to the telescope Square Kilometer Array (SKA), a giant radio telescope project consisting of several interferometric networks in metric and centimetric wavelengths and which will have a collecting surface equivalent to one square kilometer. It has just made it possible to study the shock wave resulting from a collision of clusters of galaxies extending over 6.5 million light-years.

As part of the standard cosmological modelthe gravitation specific to the black matter caused his collapse very early in the history of the observable cosmos, bringing with it the collapse of ordinary matter that gave rise to galaxies. These, in turn and always following the concentration of the black matterwill collect in filaments and also in cluster of galaxies containing hundreds or even thousands of galaxies.

The observable cosmos is expanding of course, but, just as at the level of the Solar system or some stars in a galaxy, this expansion is sometimes thwarted by the gravitational force of matter until it also dominates the repulsive effect of thedark energy. It is for this reason that the andromeda galaxy will eventually collide with the Milky Way and that we observe for example with Hubble not only colliding galaxies but also titanic collisions of clusters of galaxies.

Shock waves that indirectly radiate electrons

A few years ago, a new network of radio telescopes was inaugurated in South Africa. It is MeerKAT and it is composed of 64 parabolas radio individual 13.5 m in diameter and spread over an area of ​​8 km. Today, a team of radio astronomers who have used the data from this instrument, reveals that they provide the most detailed images of the shock wave, comparable to that of an explosion caused in the intergalactic medium by the collision which has was followed by merger of two clusters of galaxies and which gave rise to the cluster known as Abell 3667 about a billion years ago.

The cluster is mentioned in the catalog ofstars of the same type whose constitution was initiated by theastronomer American George Ogden Abell who published a first version in 1958. It now contains more than 4,000.

It clearly appears on the images in the radio domain that the formation of Abell 3667 was therefore accompanied by the equivalent of a supersonic boom in the intergalactic medium and hot plasma which bathes the clusters. The main structure observed spans nearly 6.5 millionlight years. Remember that the visible disk of our Milky Way made up of stars has a diameter of only 100,000 light-years. One can measure what the extent of the shock wave represents by seeing part of the X-ray image of it on the photography from synthetic above to false colors. Details of the researchers’ findings regarding Abell 3667 are available in a paper filed at arXiv.

Francesco de Gasperin (University of Hamburg and INAF), main author of the article, explains about the structures revealed by the MeerKAT images in a statement from the South African Radio Astronomy Observatory (SARAO) that they are ” full of surprises and much more complex than we initially thought. The shock waves act like giant particle accelerators which accelerate the electrons to gears close to the speed of light. When these fast electrons pass through a magnetic fieldthey emit the radio waves we see “.