Friday, November 24, 2006

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.

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Anonymous Vasha said...

Re "klicks per second": In a science fiction novel I just read, k/s was pronounced "kisses". It's not great, but it may grow on me. Any other suggestions?

3:25 PM  
Blogger Dr. Vector said...

Kisses, huh? I can't help but think that this will lead to jokes about sci/fi nerds only getting kisses in books. I guess miles per hour would then be "umfs"?

On hypervelocity stars and our hypervelocity galactic cluster. They're both moving about the same speed. What if the "hypervelocity" stars are really standing still, universe-wise, and they only appear to be moving so fast because our galaxy is speeding past them? It would be easy enough to see if the hypervelocity stars are all moving in the same direction, and if that direction is opposite the direction of our galaxy. The fact that the test is so easy, and yet I haven't seen it proposed as an explanation,
probably means some giant NASA brain looked into it and ruled it out. Still, it makes you think about velocity and frames of reference.

6:39 PM  
Anonymous Vasha said...

Yeah, the fact that the speed of the hypervelocity stars is given relative to the rest of the galaxy confuses things. A quick reading of the sources in that Wikipedia article didn't turn up any calculation of how they're moving relative to the cosmic background. However, the articles said that the favored scenario for how they acquired their velocity is a close encounter with the galactic black hole; so other scenarios, such as the one you mention, were presumably considered.

12:43 AM  

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