Robert G. Seeberger wrote:
I found calling the galaxy a "dark matter" galaxy a little misleading. The implication is that it's made up of an unknown type of matter. This galaxy is a galaxy formed from neutral hydrogen that never started forming stars. (It may have "dark matter" in it too, who knows.) It's still really cool, though, to think there are all these invisible galaxies out there. I want to see the image of the radio data and see how they classify it, but I couldn't find one yet.http://www.spaceref.com/news/viewpr.html?pid=16226
A British-led team of astronomers have discovered an object that
appears to be an invisible galaxy made almost entirely of dark
matter - the first ever detected. A dark galaxy is an area in the
universe containing a large amount of mass that rotates like a galaxy,
but contains no stars. Without any stars to give light, it could only
be found using radio telescopes. It was first seen with the University
of Manchester's Lovell Telescope in Cheshire, and the sighting was
confirmed with the Arecibo telescope in Puerto Rico. The unknown
material that is thought to hold these galaxies together is known as
'dark matter', but scientists still know very little about what that
is.
There's a great picture on the APOD site of an intermeidary between this galaxy and normal galaxies: http://antwrp.gsfc.nasa.gov/apod/ap980715.html
The bright spot at the center where the star formation occurs is the visible galaxy, which is classified as a blue amorphous/blue compact dwarf galaxy. The blue in the image is the 21 cm radio data--the non-starforming neutral hydrogen--and sure looks like a regular old spiral galaxy.... I think there have been other dwarf galaxies found that have also turned out to be the star-forming centers of otherwise dark galaxies. So I'm not too surprised to find out that there is an HI galaxy that has no star formation at all. It'll be interesting to see if the percentage of them (and of other matter that is dark but not exotic, like brown dwarfs) is high enough to eliminate the dark matter problem.
Amanda
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