From: Philipus Parera <[EMAIL PROTECTED]
>*Astrophysics* > >*The prints of darkness* >May 15th 2007 > From Economist.com >http://www.economist.com/daily/news/PrinterFriendly.cfm?story_id=9177524&top_story=1 > >*A ghostly ripple of dark matter is seen by the Hubble space telescope* > >NASA > >NASA > > >EITHER Newton and Einstein were wrong, or there >is something missing from the universe. The >reason is that galaxies do not behave in the way >that they should if the laws of gravity are >correct. Most galaxies rotate at a speed that >should cause them to fly apart if all that holds >their visible matter together is gravity as >physicists understand it. So either that >understanding is flawed, or there is more to the >average galaxy than meets the eye. > >Most physicists tend to the latter opinion. They >think the universe is stuffed with invisible >dark matter composed of particles very different >from the ones that make up visible matter, and >it is the gravity of this dark matter that holds >galaxies together. Their equations all make >sense if that is true. The problem is that dark >matter is invisible. But a set of results from >the Hubble space telescope, released on Tuesday >May 15th (ahead of publication in the >/Astrophysical Journal/, in June), suggest that >dark matter may finally have been seen. > >A year or two ago James Jee of Johns Hopkins >University in Baltimore and his colleagues >trained Hubble on a cluster of galaxies five >billion light years from Earth, and used a >technique called gravitational lensing to work >out how mass is distributed within this cluster. >A gravitational lens is formed when light is >bent by a massive object. Einstein predicted the >distortion of light in this way in 1915, as part >of his general theory of relativity. Three years >later a British physicist, Arthur Eddington, >watched what happened to light from stars that >were close in the sky to the sun during a solar >eclipse. Sure enough, this light was bent by the >mass of the sun, confirming Einsteins theory. > >By looking at how the faint light from galaxies >behind the cluster they were studying was >distorted by that cluster, Dr Jee and his team >created a map of the distribution of its mass. >They then compared that with what they could >actually see. Instead of finding that the mass >coincided with the location of the ordinary >matter of stars, as had been seen in >observations of other clusters, they found a distortion. > >After tryingand failingfor many months to >explain this distortion away, they accepted that >it was real, and sought to explain it. The most >plausible explanation is that the cluster >contains a distinct ring of dark matter without >any accompanying ordinary matter. > >To try to find out where this ring had come from >the astronomers trawled through previous >literature on the cluster in question. They >found an earlier suggestion that there had been >a truly enormous collision between it and one of >its neighbours between one and two billion years >ago. This work, published in 2002 by Oliver >Czoske of Bonn University in Germany, was based >on an analysis of the distribution of visible matter in the neighbourhood. > >Dr Jee and his colleagues think that the ring is >evidence of this collision. When the impact >happened, the dark matter in the clusters also >collided. It then rebounded in the way that a >ripple indicates that a stone has been thrown >into a pond. And that rippling ring may be proof >that Newton and Einstein were right after all.
