NBI Lecture by Rashid Sunyaev: Richness and Beauty of the Physics of Cosmological Recombination – Niels Bohr Institute - University of Copenhagen

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NBI Lecture by Rashid Sunyaev: Richness and Beauty of the Physics of Cosmological Recombination

Niels Bohr Lecture by Rashid Sunyaev

About the speaker: Professor Rashid Sunyaev is director of the Max Planck Institute for Astrophysics in Garching, Germany and head of the High Energy Astrophysics Department at the Space Research Institute (IKI) of the Russian Academy of Sciences. Professor Sunyaev has made important theoretical contributions to our understanding of the processes near black holes, as well as to the cosmological background radiation as a tool to provide information about the large scale structure of the Universe.

His name is permanently associated with the Sunyaev-Zel'dovich effect on the cosmic microwave background adiation. Along with his theoretical work, Professor Sunyaev has since the 1980s been the principal driving force behind the Russian space effort in the field of high energy astrophysics. As one of the most prominent astrophycisists of his generation Professor Sunyaev has won many international awards, most recently in 2008 with the Crafoord Prize and the Karl Schwarzschild Medal.

Abstract: The initial temperature of radiation in our Universe was very high and hydrogen and helium were completely ionized. At redshifts z ~ 1400 the temperature dropped to 3000 K and, according to the Saha equation, the recombination of hydrogen should occur. In reality this process is strongly delayed. Process of recombination defined the position and 
the width of the "last scattering surface" which is crucial for the formation of the observed angular fluctuations of cosmic microwave background radiation, acoustic peaks and barionic oscillations. The recombination of hydrogen occurs under conditions of very low plasma 
density and in the presence of black body radiation. As a result, usually insignificant atomic processes begin to play a role.

The recombination of hydrogen and helium leads to the appearance of emission lines in centimeter and decimeter spectral bands. Observations of these lines will make it possible to check the predictions of the big bang recombination theory and will open new ways to measure the density of barions, the CMB monopole temperature and specific entropy of the Universe, to check the presence of any significant energy release in early Universe (for example due to decay of unknown particles). Observations of helium lines originated at redshifts 6000 and 2500 will open a way to measure the prestellar abundance of helium in the Universe.