By Ron Cowen
VANCOUVER, Canada — Hidden in the peaks and valleys imprinted on the cosmic microwave background — the radiation leftover from the Big Bang — is a wealth of information not only about the early universe but the distribution of matter throughout the cosmos.
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On December 8, researchers at the Texas Symposium on Relativistic Astrophysics in Vancouver reported reading some of these imprints to identify three previously unknown galaxy clusters. The find bolsters using the cosmic microwave background as a tool for understanding how the universe’s galaxy composition has changed over time. This understanding is critical for analyzing the fingerprints of dark energy, the mysterious force that is revving up the rate at which the universe expands.
On their journey to Earth, photons from the microwave background collide with huge clusters of galaxies, millions of light-years long, which are bathed in hot gas. When the photons strike energetic electrons in this hot gas, the photons gain energy. At microwave energies, therefore, the intensity of the microwave background ought to decrease in the direction of a galaxy cluster, because photons there would be kicked to higher energies. This energy shift, known as the Sunyaev-Zel’dovich, or SZ, effect, was predicted by Rashid Sunyaev and Yakov Zel’dovich in 1980.