In the very early days of our Universe, just over 13 billion years ago, there was very little structure. There were stars, and they were forming at a rapid rate, kicking off what's known as the Stelliferous Era. But the enormous, majestic galaxies that we see today, including our Milky Way galaxy, hadn't formed yet.
The first galaxies to form were dwarf galaxies, and over time, they merged together to build the types of spiral galaxies that we see today. Astronomers know that's what happened, but the exact timeline for the Milky Way has been unclear. Now a new study published in Nature Astronomy has revealed some of the detail in the formation of our home galaxy.