||The English used in this article may not be easy for everybody to understand. (May 2013)|
The Great Attractor is a localised concentration of mass equivalent to tens of thousands of Milky Ways. It is known by its effect on the motion of galaxies over a region hundreds of millions of light years (mly) across.
These galaxies are all redshifted, in accordance with the expansion of the Universe. They are receding relative to us and to each other, but the variations in their redshift reveal the existence of the Attractor. The variations in their redshifts range from about +700 km/s to -700 km/s, depending on the angular deviation from the direction to the Great Attractor.
The position of the Great Attractor was finally worked out in 1986. It is between 150 and 250 million light years (47–79 million parsecs) away. Objects in that direction lie in the Zone of Avoidance (the part of the night sky obscured by the Milky Way galaxy) and so are difficult to study with visible wavelengths. However, X-ray observations have revealed that the region of space is dominated by the Norma Cluster, a massive cluster of galaxies, with large, old galaxies, many of which are colliding with their neighbours, and/or radiating large amounts of radio waves.
In 2005, astronomers conducting an X-ray survey of part of the sky known as the Clusters in the Zone of Avoidance. The survey confirmed earlier theories that the Milky Way galaxy was in fact being pulled towards a much more massive cluster of galaxies near the Shapley Supercluster which is beyond the Great Attractor.
Related pages [change]
- Rees, Martin 1999. Just six numbers: the deep forces that shape the Universe. Weidenfeld & Nicolson, London.
- R.C. Kraan-Korteweg 2000. Lecture Notes in Physics 556. edited by D. Pageand J.G. Hirsch, p301 Springer, Berlin.
- One theory claims the Great Attractor is a supercluster (possibly the Shapley Supercluster), "with the Norma Cluster near its center". (NASA's Ask an Astrophysicist: The Great Attractor)