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The Question

(Submitted April 01, 2008)

Okay well, I have really been wondering about something I've heard of before and that I know isn't too widely known. How much do you know about Dark Galaxies? I've heard that possibly dark galaxies are comprised of most of the matter in the universe from dark matter, or perhaps it contains tons of black holes and dead stars. I'm not sure and I would like to know what you know about the topic since I have been looking around and didn't see a topic on Dark galaxies just yet.

The Answer

First, good luck with your studies. Actually most of the mass of most galaxies is already composed of dark matter. It is this additional mass that we can't see that keeps rotating galaxies from flying apart. However, there are some candidates for truly dark galaxies, which have very little star formation. These are still detectable via radio waves from the hydrogen gas mixed in with the dark matter.

Details can be found at:
http://www.newscientist.com/article.ns?id=dn7056
http://arxiv.org/abs/astro-ph/0310192
http://en.wikipedia.org/wiki/Dark_galaxy_(astronomy)

Hope this helps,
Mike and Georgia
for "Ask an Astrophysicist"

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