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As astronomical images go, a face-on view of a spiral galaxy is pretty sexy. Today the European Southern Observatory revved up the sex appeal when it showed off infrared images of six spirals that have been "stripped bare" of their galactic dust and gas, revealing the naked stars within. Infrared-sensitive instruments are particularly good at seeing through the dust that obscures stars, and the ESO's HAWK-I is one of the world's latest and greatest infrared cameras. These six galaxies are part of a study of spiral structure led by ESO researcher Preben Grosbol. The images help astronomers understand how stars in such galaxies form such complex and beautiful spiral patterns. Can you guess which galaxy set off a supernova that was spotted by a Japanese astronaut in 2007? For the answer, check out the ESO's image advisory. And for more sexy astronomical views, take a peek at this beauty, and this one, too. Don't worry: They're both rated G ... for galaxy.
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Unreal, can't wait to see that the next 20 years holds for us!
It appears that galaxies always rotate in a counterclockwise direction. Is that true and if so, why?
Two of the four in these images rotate counter-clockwise, and four rotate clockwise. That's simply because we happen to be on one side or the other of the galaxies we're viewing, though. On Earth we assigned an arbitrary axis of North/South coinciding with the axis of rotation of the planet; the Universe as a whole has no such axis. There was a project at Galaxy Zoo in which some astronomers were checking to see if the observed rotational directions of galaxies showed a bias, because on average, we should see a 50/50 split. Based on current observations there's no bias either way, although galaxies close to each other seem more likely to be rotating in the same direction from our perspective. (I was a Galaxy Zoo participant for a couple of years; you can read about it at http://www.galaxyzoo.org/story.)
So, we see what we see because of where we are relative to the other galaxies we observe. To them, the Milky Way rotates clockwise or counterclockwise (or however these hypothetical aliens would put it) based on which side they're on.
I think galaxies that are "stripped" of their dust and gas element will show us much about gravity and its affect on galactic formation. Was it actually stripped or was it more efficient in utilizing all the particulates/matter? Cool questions to consider.
Darrell: If I'm not mistaken, it's not that the galaxies are stripped, it's that viewing them with an infrared camera instead of a visual light camera allows us to see through the dust. Sort of like those X-ray glasses that they sell in comic books, except that this actually works.
More re Darrell's post (I should have looked first): you can google more pics of these galaxies, mostly in visible light, and verify that they look hazier in visible light. Here are a couple, starting from the upper-left pic in this blog; the orientation is not always the same (i.e. which direction is "up"):
http://www.gemini.edu/node/10979 = NGC 5426 (the one on the left)
http://lapalmaisland.blogspot.com/2010_01_24_archive.html = NGC 4321 = M100
http://apod.nasa.gov/apod/ap060827.html = NGC 1300
mucho cool
So what's new here? We've had a good grasp of the spiral structure of many galaxies since the 1920s. And we've had IR photos for almost as long.
Accounting for the spiral structures has proven to be difficult, and I suspect it will remain so for a while longer, no matter how many more photos of spirals we accumulate.
They do look nice, but I always thought the photos with gas and dust lanes included looked pretty good too.