Runaway Star

(2005 repost...)

Jack Williamson's classic Legion of Space novel features Barnard's Runaway Star and the evil Medusae who inhabit that system invading Earth. John W. Campbell Jr.'s The Black Star Passes also features a invading star. E.E. "Doc" Smith did both one better and had the planets in two galaxies form when those two galaxies "collided".

Here's a star (for real) that's being flung from our galaxy at over 1.5 million miles per hour.