Discovery of the Day: The "Dark Matter Halo"
The Hubble Space Telescope image above indicates that a huge ring of dark matter surrounding the center of galaxy cluster CL0024+17 located in Pisces. The many spectacular galaxies are part of CL0024+17 itself, typically appearing tan in color along with several unusual and repeated galaxy shapes, typically more blue, and multiple images of distant galaxies, showing that the cluster is a strong gravitational lens. The ring's discovery is among the strongest evidence to date that dark matter exists.
Gravitational lensing occurs when a massive galaxy in the foreground bends the light rays from a distant galaxy behind it, in much the same way as a magnifying glass would. When both galaxies are perfectly lined up, the light forms a circle, called an “Einstein ring”, around the foreground galaxy. If another more distant galaxy lies precisely on the same sightline, a second, larger ring will appear.
Original observations made in 1970 revealed that gravitational motions of gas clouds in the Andromeda galaxy were occurring at speeds far greater than the entire observed mass of that galaxy could account for. Similar problems detected in the 1930's involving motions of entire galaxies had long been disregarded. Later observations confirmed that so-called "ordinary matter" is insufficient to account for observed gravitational effects in the cosmos. Thus the universe must contain huge amounts of "dark matter," that we cannot observe and the composition of which we do not know.
In 1998 reports of observations of distant supernovae revealed that the expansion of the universe was not slowing, as would be expected from long-term effects of gravity, but was instead accelerating. Something was overcoming the gravitational power of all of the matter in the universe. The acceleration, moreover, has not been present from the Big Bang on. For billions of years the speed of expansion slowed. Then, about 5 billion years ago, acceleration began. Obviously energy--a lot of it--- was required to explain these phenomena. This is "dark energy." We cannot detect it and currently know almost nothing about it.
Today scientists believe that 5% of the universe consists of "ordinary" [observable] matter, 23% of "dark" matter and 72% of "dark energy."
Casey Kazan
"The dark matter distribution in the foreground galaxies that is warping space to create the Einstein's telescope, the gravitational lens, can be accurately mapped."
"The computer-modeled dark matter ring of CL0024+17 spans about five million light years and been digitally superimposed to the image in diffuse blue."
Casey, you really should practice your writing. Some of your sentences are bordering on unintelligible. Try writing with less haste, and try using shorter sentences. You have a great website, and you should not diminish it by writing sloppily.
Posted by: qed | December 16, 2009 at 08:51 AM
@qed: Hear hear: reifying what is already a mystery (Dark Matter)by a digital superimposition is stretching things a Bit don't you think? Sci-Fi?
Posted by: Richard Murphy | December 17, 2009 at 09:36 AM