The Gaia-Enceladus fusion forged our galaxy

Between 8 and 10 billion years ago, one of the greatest events in the formation of the Milky Way took place: it collided with a dwarf galaxy called “Gaïa-Enceladus”. Such episodes are not uncommon in the history of galaxies and help to create them: they relentlessly tend to approach each other, attracted by gravity.

The larger ones eat the smaller ones, a law that also applies in the Cosmos, where the most massive galaxies suck up the smaller ones. Thus, Gaia-Enceladus, which contained at most 1% of the stars that make up the Milky Way, was absorbed. Details of this galactic fusion were provided by a team from the Harvard & Smithsonian Center for Astrophysics (CfA) in a study published in December 2021 in the journal The Astrophysical Journal.

That galaxy collisions are not uncommon

The history of galaxies is far from linear. The oldest are found in the early universe and would have formed only a few hundred million years after the Big Bang. A number of years that seem high, but turn out to be insignificant in relation to Kosmos’ total age, namely 13.8 billion years! At that time, the universe was much smaller and denser than it is now, and galaxy aggregations were common. With its expansion, these became so rare as the stars became more and more scattered.

The Milky Way is no exception and has undergone several collisions throughout its history, including the one specifically studied by researchers with Gaia-Enceladus. To reconstruct the scenarios of these catastrophic encounters, scientists are targeting the remnants of these galaxies, in other words, the stars that once formed them. Because galaxies are mostly composed of disorganized gas and dust, the probability of a collision between two stars is very low. On the contrary, these are preserved, and it is they who will enable scientists, much later, to reconstruct the history of these galactic fusions.

Leave a Comment