The formation of the Sun, the Solar System and the subsequent emergence of life on Earth may be a consequence of a collision between our galaxy, the Milky Way, and a smaller galaxy called Sagittarius, discovered in the 1990s to be orbiting our galactic home.

Astronomers have known that Sagittarius repeatedly smashes through the Milky Way’s disc, as its orbit around the galaxy’s core tightens as a result of gravitational forces. Previous studies suggested that Sagittarius, a so called dwarf galaxy, had had a profound effect on how stars move in the Milky Way. Some even claim that the 10 000 times more massive Milky Way’s trademark spiral structure might be a result of the at least three known crashes with Sagittarius over the past six billion years.

A new study, based on data gathered by ESA’s galaxy mapping powerhouse Gaia, revealed for the first time that the influence of Sagittarius on the Milky Way may be even more substantial. The ripples caused by the collisions seem to have triggered major star formation episodes, one of which roughly coincided with the time of the formation of the Sun some 4.7 billion years ago.

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