In other words, at that time the Milky Way had a cosmic cataclysm. The other galaxy involved was named the ‘Gaia Sausage’. It left behind a mess of stars with some rather unusual orbits. The Sausage galaxy was massive, Its total mass in gas, stars and dark matter was more than 10 billion times the mass of our Sun. Using mathematical models to rewind and unravel their paths, the researchers arrived at a monumental event in the history of our galaxy roughly 8 to 10 billion years ago. the Milky Way could have been fractured in impact.
This new model puts a new spin on previous observations by suggesting a younger Milky Way was hit with an incoming ball of stars and dust, contributing to a dense nucleus that came to be surrounded by a halo. The astronomers used data (parallaxes and velocities of Milky Way stars) from ESA’s Gaia satellite. At the cosmic scale, transformations occur and never stop. In around 4 billion years, Andromeda and the Milky Way will swirl together and mix stars in a slow dance that will once again change the shape of our galaxy in a monumental way.