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Fraser
2004-Sep-08, 04:17 PM
SUMMARY: Astronomers theorize that most of the mass in the Universe is dark matter; it's invisible and detectable only by the pull of its gravity on objects. This dark matter is in long filaments, and galaxy clusters form where these filaments intersect. NASA's Chandra X-Ray Observatory has found a hot gas cloud hundreds of thousands of light-years across in the the Fornax galaxy cluster is collapsing towards an invisible centre of gravity. Computer simulations have accurately predicted this kind of interaction between galaxy clusters and filaments of dark matter, so this discovery will give astronomers a chance to understand the process better.

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StarLab
2004-Sep-08, 05:27 PM
But how can we be completely sure that it's dark matter we're detecting?

antoniseb
2004-Sep-08, 06:25 PM
Originally posted by StarLab@Sep 8 2004, 05:27 PM
But how can we be completely sure that it's dark matter we're detecting?
We aren't. Here are the clue:
It has more gravity than normal matter could have without being luminous.
We know this because of how it distorts images of galaxies behind it.

Fraser
2004-Sep-09, 12:05 AM
Hi Starlab, I got this answer for you from the folks working with Chandra.



We canít be completely sure that dark matter is pulling the core of the Fornax cluster and the outlying group of galaxies toward a common center of gravity. The directions of their motion could be a coincidence, but strong circumstantial evidence indicates that an unseen source of gravity is pulling them.

This evidence consists of measurements of the motions of many galaxies in the cluster with optical telescopes, and measurements with X-ray telescopes of the pressure of the hot gas that fills the cluster, which give the total mass of the cluster. The total mass determination shows that dark matter must comprise about 80-90% of the mass of the Fornax cluster.

Wallace Tucker
Science Spokesperson

StarLab
2004-Sep-09, 12:28 AM
How about this for an analogy? I think Antoniseb would recognize this:

Let's say your universe is an ocean, and the ships on the ocean are galaxies. Those that are close together would inherently decrease their distances from each other. Those farther apart would not be affected by those distant ships, and their velocity would most likely take them in the opposite directions. So things that are already close together will simply get closer, and things farther apart will stay that way.

Guest
2004-Sep-09, 09:48 AM
These galactical collisions make you wonder just how long will "this" universe survive. If the red shift theries are correct then it will keep expanding until every single atom is universally apart from every other atom. The afore mentioned collisions will cause both the destruction of and then rebirth of stars. Are we looking at hundreds of billions of years or billions of billions of years until the "end"?