Speed demons of the galaxy
I had no idea that some stars are careening through the galaxy like pinballs while the rest more or less behave. The first I heard of the existence of these things was on the Astronomy Picture of the Day site, which is where I stole the above image from. APD has this to say: "Like a ship plowing through cosmic seas, runaway star Alpha Cam has produced this graceful arcing bow wave or bow shock, moving at over 60 kilometers per second and compressing the interstellar material in its path." By comparison, the New Horizons probe that launched earlier this year is headed to Pluto at 16.2 km/s, which makes it the fastest spacecraft ever launched*, but it's still doing just over a quarter of the speed of Alpha Cam.
*Voyager I will leave the solar system doing just over 17 klicks per second, but it launched slower and picked up a good chunk of that velocity from gravitational slingshots around Jupiter and Saturn.
Anyway, following the links from the APD page took me to Wikipedia and eventually to this article on hypervelocity stars, which make even runaway stars look slow. One such star, with the delightfully poetic name of HE 0437-5439, is moving at 723 km/s. How fast is that? Pluto is about 4.5 billion kilometers from Earth. New Horizons, which launched this spring and is already almost to Jupiter (it will pass Jupes in about three months), will take 9 years to get there. Alpha Cam would make the same trip in a little under two and a half years. And the fast mover mentioned above would get there in 72 days. In other words, if HE 0437-5439 passed Earth right now, it would pass Pluto a couple of weeks before New Horizons passes Jupiter. And New Horizons is hauling ass.
Hold onto your butts--New Horizons takes off on an Atlas V delivering more than two million pounds of thrust. ROCK.
Anyway, does anyone know if any of these hypervelocity stars have shown up in science fiction stories? The closest thing I can think of is H.G. Wells's story "The Star", about a rogue star that passes through the solar system and wrecks shop. The story is very short and you can read it for free here or here. If you know of any other occurrences, let me know.
UPDATE: It turns out that we're the speed demons of the universe. Forget about hypervelocity stars, how about hypervelocity clusters of galaxies? The galaxies in our local group, including our own home-sweet-home Milky Way, are moving at about 600 kilometers per second relative to the cosmic background radiation. Read all about it here.