One observation in space has so far made astronomers despair: the satellite galaxies of the Milky Way are all arranged in one disk, although according to recognized models they should actually be randomly distributed. But new calculations bring the solution to the riddle.
For decades, astronomers have puzzled over why the Milky Way’s satellite galaxies are not randomly distributed, but lie within one disk. This could not be explained with the standard cosmological model. But the whole thing is not so mysterious, but pure coincidence, as an international research team has now discovered through precise measurements. The supposedly unusual arrangement dissolves again within a few hundred million years due to the movement of the galaxies, the scientists write in the journal “Nature Astronomy”.
“The companions of the Milky Way are almost aligned in the sky – and this has puzzled astronomers for decades,” explains co-author Carlos Frenk of Durham University in the UK. Because if the satellite galaxies are aligned in the sky, they must all be within a thin disk in space. “And explaining that is extraordinarily difficult for cosmology.” So difficult that it has already cast doubt on the standard cosmological model and, in particular, on the researchers’ idea of ??the mysterious dark matter.
Because according to current knowledge, the visible matter – i.e. stars, planets or gas clouds – only contributes a fifth to the total mass of the cosmos. Eighty percent of the mass consists of dark matter. This is completely invisible – hence its name – and reveals itself only through its power of attraction. Dark matter plays a crucial role in the formation of galaxies in the cosmos.
Computer simulations show what this looks like: Normal matter, i.e. all stars, accumulates in large, spherical concentrations of dark matter. The galaxies that form there are then distributed completely randomly – a concentration in a disk cannot be explained with the current model and is also not shown in computer simulations.
Frenk and his colleagues have now used the best data so far from the European Space Agency’s Gaia space telescope to solve this mystery. Gaia has been in space since 2013 and provides precise position and motion data for around a billion stars – not only in our Milky Way, but also in its satellite galaxies.
The evaluation of the data caused a surprise. Until now, astronomers had assumed that the small galaxies always moved on orbits within the disk. But that is not the case. The conclusion of Frenk and his colleagues: The currently observed concentration of satellite galaxies in a disk is purely accidental. Within a few hundred million years – a short time in cosmological terms – the disc has disappeared and the galaxies are once again evenly distributed around the Milky Way.
The team then took another look at the best computer simulations of galaxy formation to date. And in fact, such random discs could also be detected there. Until now, such random phenomena had been overlooked because researchers had only been looking for evenly rotating disks from satellite galaxies.
“We have thus solved one of the currently greatest challenges of the cosmological model,” says Frenk. “The dark matter model gives us a remarkably accurate description of how the Universe evolved.”
