After 50 years, the mystery of the satellite galaxies of the Milky Way has finally been solved: their bizarre alignment, in fact, which appears to form a huge and thin rotating disk, has puzzled astronomers since its discovery in 1970, and has put in discussion the current models that describe the universe.
The solution comes from a study published in the journal Nature Astronomy and led by the Finnish University of Helsinki and the British University of Durham, which used the data provided by the European Space Agency's (ESA) Gaia satellite: the alignment of the galaxies would actually be a momentary coincidence, which was formed very recently from the cosmic point of view and which will dissolve just as quickly.
The standard model of cosmology, the theory that explains the formation and evolution of the structures that make up the universe, indicates that galaxies form inside clusters of cold dark matter, an element still unknown which should make up about 27% of the cosmos .
However, this model does not contain any mechanism that would allow satellite galaxies to arrange themselves in a disk: instead they should cluster in a more globular or spherical shape.
In an attempt to shed light on this mystery, researchers led by Till Sawala of the University of Helsinki have used data from Gaia, which is drawing a six-dimensional map of the Milky Way: thanks to the ESA satellite, the authors of the study have managed to build computer simulations that show both the movements of galaxies in the past and those in the future.
“We now know that the disk of satellite galaxies is just a random and temporary alignment, due to the fact that they were in the right place at the right time,” comments Carlos Frenk of the University of Durham, co-author of the study: “In a billion years will no longer exist”, a mere blink of an eye in cosmic time.
