Astronomers searching for evidence of the mysterious energy that is speeding up the expansion of the Universe have discovered three new galaxy clusters. They used a microwave survey technique that could rival existing ways of searching for dark energy. The discovery is the first step towards a catalogue of thousands of galaxy clusters, whose evolution in the early Universe reflects the tug of war between gravity and dark energy, the repulsive force that seems to make up three-quarters of the total mass-energy in the Universe. The astronomers found the three clusters by searching for shadows in the cosmic microwave background, the relic radiation of the Big Bang, using a microwave telescope located at the Amundsen-Scott South Pole Station in Antarctica (see 'The South Pole Telescope').
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