Saturday, May 19, 2007
This is not a real ring of galactic clusters. It is an optical illusion formed by a gravity source in the middle which bends light passing on both sides so that the light comes to a focus,after traveling 5 billion light years, here. It is evidence for the existence of considerable amounts of Dark Matter. Dark mMatter is the material astronomers cannot see but would really like to be there if the universe is ever to rebound rather than keep on expanding forever. This doesn't prove there is enough Dark matter of this but it is a pointer. My intuitive guess is that the more matter we find the closer we will get to a closed universe but I doubt if we will ever quite get there - but this is an almost religious speculation more than a scientific one.
The ring , 2.6 million light-years across, was found in the cluster CL0024+17, located five billion light-years from Earth. A member of the team that spotted the dark matter ring, said they unexpectedly found the ring while mapping the distribution of dark matter within the cluster, by observing how its gravity bends the light of more distant background galaxies. Computer simulations of the gravitatonal refraction reveal that as the clusters collide, the dark matter falls to the centre of the combined cluster and "sloshes" back out.