Chushiro Hayashi Prize awarded to Eiichiro Komatsu

The Astronomical Society of Japan recognised Eiichiro Komatsu for "Precision Cosmology based on the Cosmic Microwave Background", the left-over radiation from the Big Bang at the beginning of the Universe. Komatsu analysed and interpreted the CMB data that was measured by the WMAP satellite mission, and in particular determined the cosmological parameters as well as testing theories of inflation.

In analysis of the CMB, it is usually assumed that the small temperature fluctuations, the signature of the tiny primordial density fluctuations, are distributed randomly in a Gaussian field. While some inflationary scenarios predict that the fluctuations should indeed be nearly Gaussian, more complex models predict deviations from a Gaussian field. The presence of any non-Gaussian features in the observed CMB are therefore a powerful test for various inflationary models. Komatsu has done pioneering work on testing inflation using non-Gaussian features.

From 2001 to 2010, Komatsu worked as a key member of the WMAP team on data analysis and the theoretical interpretation. He was the first author of some of the highly cited WMAP papers. One of the important contributions he made was to show that the distribution of CMB temperatures measured by WMAP obeys Gaussian statistics to high precision, which provides the strongest evidence for the idea that the structures in the Universe originated from quantum fluctuations during inflation.

The Prize is named after Prof. Chushiro Hayashi (1920-2010), who was an internationally recognised astrophysicist, well known for his contributions to the nucleosynthesis of the early universe, stellar evolution, and the formation of Solar System. With his astrophysical calculations he showed that young stars, after their proto-star phase, follow a certain track (the Hayashi track) in the Hertzsprung-Russell diagram, contracting and decreasing in luminosity while keeping an almost constant surface temperature until nuclear fusion starts to produce energy at their core. Closely related to this development is the Hayashi limit, a zone in the Hertzsprung-Russell diagram, where no stars in hydrostatic equilibrium can be found.