The neighbouring Andromeda Galaxy and our own Milky Way are on a rapid collision course that will see them meet four billion years from now. Astronomers are now certain that the collision is inevitable. Their measurements and simulations predict the collision will be followed by a graceful dance of the two celestial bodies, lasting two million years, before their black holes finally merge to make a bigger composite galaxy.
It is unlikely that Earth’s Sun, along with other stars, will be destroyed in a mash-up, but all their relative positions will be redistributed and our solar system could be pushed to the outskirts of the merged result. “Galaxies are actually mostly empty space. So if two galaxies collide with each other the stars basically pass right between each other and the chance of two stars directly hitting each other is really, really small. In all likelihood, our solar system will not be much impacted,” said Roeland van der Marel, one of the authors of the study.
Looking from the Earth’s line of vision it seems like Andromeda is coming straight at us. However, without knowing its sideways velocity we cannot tell whether the encounter will be a close shave, a glancing blow or a distant encounter.
Observations by the Hubble space telescope have made it possible to measure Andromeda’s sideways velocity. “And with this measurement we have been able to show that Andromeda is actually coming straight at us,” van der Marel said.
As Andromeda approaches (at 400,000 kmph), the way our night sky looks will change drastically with beautiful views of the approaching galaxy two billion years from now before we become part of a much larger galactic empire.