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Astronomers Professor Chris Collins and Dr Ian McCarthy from LJMU's Astrophysics Research Institute are challenging the view that the currently preferred cosmological model of the Universe is correct by comparing recent measurements of the cosmic background radiation and galaxy clusters in two independent studies partly funded by the Science and Technology Facilities Council.

One of the cornerstones of the Big Bang theory of the Universe is the cosmic background radiation (CBR). Discovered in 1965 these electro-magnetic waves bombard the Earth continuously from all directions at harmless microwave frequencies. However, the radiation arriving here has been cooled to only 2.7 degrees above absolute zero (as it traverses deep space) by the expansion of the universe; therefore, in the distant past the temperature would have been much higher. This leads us to the conclusion that the universe had a hot origin – the so called Big Bang – nearly 14 billion years ago.

The Planck Surveyor satellite, launched in 2009 by the European Space Agency (ESA), is the latest in a line of several satellites designed to measure the temperature variations in the CBR from place to place across the sky. These tiny fluctuations slowly grow over time, eventually forming the stars and galaxies we see today. Because the radiation began its journey when the Universe was only 380,000 yrs old, these measurements provide vital information about the detailed composition of our Universe. The cosmic census provided by Planck is remarkably precise, giving us amongst other things accurate estimates of: the age of the Universe (13.82 billion years) and the amount of dark matter (31.7%) and dark energy (68.3%).

It turns out that Planck is also sensitive to the largest gravitationally bound structures called clusters, which contain thousands of individual galaxies and large amounts of dark matter. Curiously, however, Planck has found fewer clusters than was predicted based on the CBR cosmological analysis.

Now, in independent studies, the recent work of both Collins and McCarthy confirms the "Planck-cluster problem" in that there are much fewer massive clusters in the Universe than expected for the Planck best-fit cosmology, a result inviting a rethink of the underlying model.

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