It’s a definite hit. The Andromeda galaxy will collide with our very own Milky Way about 4 billion years from now, astronomers recently announced. Although the Sun and other stars will remain intact, the titanic tumult is likely to shove the Solar System to the outskirts of the merged galaxies.
Andromeda, roughly 770,000 parsecs (2.5 million light years) away, is the nearest large spiral galaxy to the Milky Way.
For decades, scientists have known that Andromeda is falling towards our home Galaxy at a rate of 110 kilometres per second and that the two might eventually collide as a result of their mutual gravity. But because astronomers could easily measure Andromeda’s velocity only along the line of sight to Earth, no one could be sure whether the future encounter would constitute a major merger, a near-miss or a glancing blow.
Thanks to the Hubble telescope, scientists have shown that a merger of Andromeda and the Milky Way is inevitable. Four billion years from now, the two galaxies will pass through each other and, 2 billion years after that, they will fall back in a permanent embrace to form a single galaxy. Learn more here.