“Think about it this way – a boomerang goes out and comes back to you if you throw it. If you throw it out at the universe, it will come back down to you on Earth.” -J. B. Smoove
Give a planet a kick, and it goes into a more distant orbit around our star. Give it a hard enough kick, and it will reach escape velocity, leaving our Solar System forever. But if you gave it an almost hard enough kick, it would travel extremely far from the Sun, but it would eventually boomerang back towards the inner Solar System, with potentially disastrous, disruptive consequences. This applies to any system (not just the Solar System), including our own galaxy.
In the Milky Way’s outskirts, there are high-velocity gas clouds, including one — the Smith Cloud — that’s moving towards us at a breakneck pace. Thanks to data from the Hubble Space Telescope, Andrew Fox and his team have just uncovered that this cloud came from our Milky Way, was almost ejected into intergalactic space, but is now on its way back, where in 30 million years it will collide with our galactic disk. The 11,000 light year-long cloud is expected to produce over 2 million new stars when it does.