It is believed that dark matter dominates all galaxies and large clusters, but astronomers have discovered a galaxy composed entirely of ordinary stars.
In our world, dark matter is many times larger than ordinary matter, from which stars, planets and ourselves are composed. It is believed that it plays a decisive role in the formation and evolution of large-scale structures of the Universe, galaxies and their clusters. Here, its gravity dominates, determining the life of gas clouds and stars. Moreover, they assume the existence of "dark galaxies", completely devoid of ordinary matter and stars. Candidates are also known: for example, the Dragonfly 44 galaxy, discovered three years ago, is 99.99 percent dark matter.
This makes the recent discovery of astronomers from Yale University, which they report in the journal Nature, unexpected: a galaxy practically devoid of dark matter. It was possible to observe NGC 1052-DF2 using the Dragonfly Telephoto Array telescope, designed by Professor Pieter van Dokkum in collaboration with colleagues from Canada. Even outwardly, it stands out against the general background. According to scientists, who first examined all the details of the structure, it is "transparent" and looks like an extremely rarefied small cluster, in which there are occasionally a few compact groups of stars.
More powerful telescopes at the WM Keck Observatory in Hawaii have made it possible to establish the speeds of a dozen such clusters in NGC 1052-DF2. They also turned out to be several times smaller than usual - less than 10 km / s. Finally, astronomers estimated the mass of the galaxy, which almost coincided with the mass of all its stars: "If there is dark matter, then it is extremely small," - explains Van Dokkum.
The scientist adds: “This invisible mysterious matter is an essential component of any galaxy. It was extremely unexpected to find a galaxy without her. This forces us to re-look at the usual ideas about the structure of galaxies and shows that dark matter is real. It leads its own existence, separate from other components of galaxies. It can also be assumed that there is not only one - standard - mechanism for the formation of galaxies."
Sergey Vasiliev