The wildest ride in the galaxy is found on hypervelocity planets. These worlds got too close to the supermassive black hole at the center of our galaxy, and have been flung away at a twentieth of the speed of light.
While rogue planets are common enough, these hypervelocity planets represent a much rarer case and can only be formed by a star system - specifically, a double star system - coming into contact with Sagittarius-A*, our galaxy’s central supermassive black hole. Previous research has indicated that when a binary star system gets too close to Sagittarius-A*, it’s possible the system to be ripped apart, with one star entering orbit around the black hole while the other is ejected at enormous speeds.
Now researchers at the Harvard-Smithsonian Center for Astrophysics say the same phenomenon could work for any planets orbiting these double stars. Let’s imagine a simple example of such a solar system, with Star A and Star B. In this system, Planet A primarily orbits Star A and Planet B primarily orbits Star B. As the binary comes into contact with Sagittarius-A*, Star A goes into orbit while Star B is ejected, zooming on a trajectory that will take it out of the Milky Way at millions of miles per hour.