Our sun and its system formed "about" 4.567 Gya. The universe, depending on your Hubble constant, is more approximate: 13 Gya. In between, the Milky Way had formed... as we know it. J. M. Diederik Kruijssen et al. are sketching the formation process.
Galaxies by now are not pure entities. They merge. Two billion years from now we are to merge with the Andromeda; I think we're too big to be a mere part of their spiral, so we'll be forming a spherical galaxy together. There's an analogy with "formation of the Earth", given that our Earth as we know it comes from a union of proto-Earth in this approximate orbit, with Theia come from outside.
So they say that 11 Gya, our Milky Way sucked in another young galaxy, the "Kraken". Then Helmi Streams and Sequoia. Then comes the mergers they knew about (but I didn't), 9 Gya - Gaia-Enceladus-Sausage. The most recent at 7 Gya is Sagittarius, which turns out to be the least massive known; I assume we gobbled in earlier dwarfs that the research cannot yet find. Sagittarius was known from previous studies so proved a good test for the method.
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