Astronomers previously thought that the galaxy was made of two separate sets of stars, but exactly how or when they came together as a mystery. Using the Gaia space telescope, these researchers were able to make more precise measurements of the position, brightness and distance of one million stars. They also look at the density of "metals," or elements without hydrogen or helium, that the stars contain. The researchers believe Gaia-Enceladus collided with the Young Milky Way about 1
, and over the course of millions of years, the Milky Way consumed the dwarf galaxy. The researchers thus said that they were through the middle of the milky way. They believe that the remnants of Gaia-Enceladus have formed the halo of the present-day Milky Way.
According to the researchers, this information provides "unprecedented detail" about the early stages of our cosmic history. Of course, it's not the first time we've heard of one's galaxy consuming another. In fact, our galactic neighbor Andromeda cannibalized a nearby galaxy some two billion years ago, and it's on track to collide with the Milky Way in the very distant future.