NASA's Hubble Space Telescope has uncovered new evidence that galaxies are embedded in and protected by halos of dark matter, the invisible form of matter that accounts for most of the universe's mass.
Dark matter is invisible and nobody even knows what it is, but it is evident by the fact that galaxies hold together at all. Some unseen substance lurks in space — concentrated in galaxies — and generated gravity in amounts well beyond the visible matter.
Peering into the tumultuous heart of the nearby Perseus galaxy cluster (located 250 million light-years away), Hubble discovered a large population of small galaxies that have remained intact while larger galaxies around them are being ripped apart by the gravitational pull of neighboring galaxies.
"We were surprised to find so many dwarf galaxies in the core of this cluster that were so smooth and round and had no evidence at all of any kind of disturbance," said astronomer Christopher Conselice of the University of Nottingham in England, and leader of the Hubble observations.
"These dwarfs are very old galaxies that have been in the cluster a long time. So if something was going to disrupt them, it would have happened by now. They must be very, very dark matter-dominated galaxies."
Full at http://www.space.com/scienceastronomy/0903...ark-matter.html
The article had a fair number of "mays" in it. DM is so vague that I doubt it though having said that, if it were shown to exist, I do have a candidate for it.
The usual reason why dwarf galaxies survive tidal pulls better than larger galaxies is precisely because they are compact. A view of the Perseus Cluster:
http://www.mistisoftware.com/astronomy/ima...041214_2000.jpg
The usual reason why dwarf galaxies survive tidal pulls better than larger galaxies is precisely because they are compact. A view of the Perseus Cluster:
http://www.mistisoftware.com/astronomy/ima...041214_2000.jpg
You actually made sense! Thank you! 
QUOTE (Beer w/Straw+Mar 17 2009, 06:05 AM)
http://chandra.harvard.edu/press/06_releas...ess_082106.html
It's been a few years since I last saw that. Clusters have lots and lots of open space. Collision is not quite correct because much of the matter goes through unimpeded. There are of course some spectacular collisions between stars and gas clouds have more chance of collisions as they can cover thousands of light years instead of just a million mile diameter star. So we have material which gets through OK but a lot still in a hot collision, held together by local gravity. The article talks as though it believes that the hot gas should hold the stars in place. Now for the fairy dust:
It does only what is wanted of it. This unknown DM interacts by gravity only. There is sufficient about to keep a gas cloud cohesive. The reason it does not form large bodies is? It has no repulsive force as in charged particles. It is not hot (as in energetic). Look at the quantity that made it through. Hardly several times as much DM as LM. A very biased article.
It's been a few years since I last saw that. Clusters have lots and lots of open space. Collision is not quite correct because much of the matter goes through unimpeded. There are of course some spectacular collisions between stars and gas clouds have more chance of collisions as they can cover thousands of light years instead of just a million mile diameter star. So we have material which gets through OK but a lot still in a hot collision, held together by local gravity. The article talks as though it believes that the hot gas should hold the stars in place. Now for the fairy dust:
QUOTE
In contrast, the dark matter was not slowed by the impact, because it does not interact directly with itself or the gas except through gravity.
It does only what is wanted of it. This unknown DM interacts by gravity only. There is sufficient about to keep a gas cloud cohesive. The reason it does not form large bodies is? It has no repulsive force as in charged particles. It is not hot (as in energetic). Look at the quantity that made it through. Hardly several times as much DM as LM. A very biased article.
You're arguing with NASA?
I sometimes get the impression that NASA's news releases are done by an office boy. They seem to be like what you'd expect of a science correspondent on a national newspaper rather than what you would expect from a "boffin". Possibly they are deliberately dumbed down for public consumption?
Although your article is a few years old and claims positive proof of DM, there are still doubts. You might check this source out which is a year old:
http://www.cosmosmagazine.com/node/2289/full
Although your article is a few years old and claims positive proof of DM, there are still doubts. You might check this source out which is a year old:
http://www.cosmosmagazine.com/node/2289/full
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