The Milky Way galaxy will collide with the neighboring Andromeda galaxy in the next 4 to 5 billion years, completely merging with it in the next 6 billion years. But that won’t be the first collision of our galaxy with another. The Milky Way is the second-largest member of the Local Group comprising at least 80 known galaxies. Satellite galaxies orbiting the giant ones end up being torn apart and ultimately merging with the massive galaxies.
The Milky Way is already merging with several satellite galaxies, but one of the most prominent mergers is with the Sagittarius dwarf galaxy. Astronomers have found evidence that Sagittarius has already passed through the Milky Way thrice in the past six billion years, which might be the reason behind our existence. But how did scientists make this intriguing discovery? How do they know the number of times the Sagittarius dwarf galaxy passed through the Milky Way? Finally, and most importantly, why is Sagittarius considered the reason behind the existence of life on Earth?