It’s a discovery that questions the history of our galaxy. While scientists believed that the majority of the dwarf galaxies around the Milky Way had been their satellites for billions of years, a new study published in the Astrophysical Journal shows that it has not.

To arrive at this conclusion, an international team of astronomers, led by Frenchman François Hammer of the Paris Observatory, drew on the latest data released by the European Gaia space mission in December 2020. This mission, called Astrometry, is based on a satellite that measures the distance between the stars very precisely in order to create a real 3D map of our galaxy.

In practice, the researchers examined the movements of 40 dwarf galaxies in the vicinity of the Milky Way. In doing so, they discovered that they were moving much faster than previously thought and much faster than the giant stars and star clusters that are known to orbit our galaxy.

It is impossible that they have long been anywhere near the Milky Way. If this were the case, their interactions with the latter would have already undermined their beautiful energies: they would therefore be much less restless … Gaia’s observations, on the contrary, suggest that these little neighbors have evolved there for a billion or two at the most, and that “Our galaxy has not or at least not yet orbited them.

No more dark matter needed!

But that doesn’t just change the history of our galactic neighborhood! It also changes what we thought we knew about these dwarf galaxies. Having withstood the onslaught of our Milky Way for so long, astrophysicists imagined they were crammed with dark matter, a substance unknown but necessary to give them enough gravity to keep them cohesive. If they are newbies, there is no need to add dark matter to their composition. So it is not just the story but all of the models that we need to review in the face of this reveal!