Dr. Rashid A. Sunyaev has made a far-reaching influence on contemporary observational cosmology through his theoretical studies of acoustic oscillations in the early universe left their imprint on temperature fluctuations in the cosmic microwave background radiation and the scattering of that radiation by hot electrons in the clusters of galaxies. He has also made significant contributions to high-energy astronomy through his theoretical research on the accretion of matter onto high-density celestial objects and the energy release mechanisms involved, as well as his leadership of international observational projects.
Small-scale fluctuations of relic radiation (with Zeldovich, Yakov B.). Astrophysics and Space Science 7: 3-19, 1970
The observations of relic radiation as a test of the nature of X-ray radiation from the clusters of galaxies (with Zeldovich, Yakov B.). Comments on Astrophysics and Space Physics 4: 173-178, 1972
Black holes in binary systems. Observational appearance (Shakura, Nikolai I. and Sunyaev, Rashid A.). Astronomy and Astrophysics 24: 337-355, 1973
Comptonization of X-rays in plasma clouds. Typical radiation spectra (with Titarchuk, Lev G.). Astronomy and Astrophysics 86: 121-138, 1980
Discovery of hard X-ray emission from supernova 1987A (Sunyaev, Rashid A. et al). Nature 330: 227-229, 1987
Dr. Rashid Alievich Sunyaev’s primary contributions are to the theories underpinning observational cosmology, which has progressed to become an exact science in this century. In a paper with Dr. Yakov Zel’dovich in 1970, examining the physical process of hydrogen recombination in the hot early universe, Dr. Sunyaev revealed that baryon acoustic oscillations (BAO) of that remote time due to the primordial fluctuations can be observed as intensity variation in today’s cosmic microwave background radiation (CMB).
As the universe expanded and its temperature decreased, protons and electrons form hydrogen atoms, with the result that interaction between matter and thermal radiation decreased drastically and the universe cleared from a state of opaqueness. Radiation from that time can be observed today as CMB. This background radiation carries information about the space-time that it has subsequently passed through, as well as memories of the primordial fluctuations. BAO in the early universe predicted by Dr. Sunyaev and Dr. Zel’dovich were actually observed by WMAP spacecraft only in 2003. Observations of BAO have played a major role in giving constraints on the universe models, such as providing the evidence of accelerating expansion of the universe. It was Dr. Sunyaev’s pioneering achievement that pointed out the possibility of using the BAO observational result for determining the cosmological parameters of the expanding universe.
Clusters of galaxies are scattered in the universe. Dr. Sunyaev and Dr. Zel’dovich showed in 1972 that the CMB spectrum is distorted by collision with hot electrons in the clusters. This effect, now known as the Sunyaev-Zel’dovich (SZ) effect, is widely believed to serve as a key principle for the study of large-scale structure.
Another noteworthy accomplishment of Dr. Sunyaev lies in his important contributions to high-energy astronomy. The greatest enigmas raised by the discovery of X-ray sources were their real identity and the mechanism of X-ray radiation. In 1973, together with Dr. Nikolai Shakura, Dr. Sunyaev succeeded in formulating a mechanism that involves matter accreting to black holes and other compact objects, providing quantitative explanations for high-energy radiation and their spectra. Known as the standard Shakura-Sunyaev model, this theory has provided the basis for describing accretion phenomena and their associated energy release around various types of objects.
Since the latter half of the 1980s, Dr. Sunyaev has expanded his activities to observational research in high-energy astronomy, taking the lead in X-ray and γ-ray astronomy satellite projects in Russia and Europe. Bringing many co-researchers together and elucidating the processes underlying hard X-ray and soft γ-ray emissions from various celestial bodies, he has made continued contributions to the development of high-energy astronomy.
For these reasons, the Inamori Foundation is pleased to present the 2011 Kyoto Prize in Basic Sciences to Dr. Rashid Alievich Sunyaev.
I was born in the middle of the Second World War in a multi-ethnic city on the former Silk Road in the former Soviet Union. At the age of 17 I went to study physics in Moscow. My introduction to Yakov Zel’dovich, the well known Soviet physicist, completely changed my life because:
1. I got the opportunity to work with that active, hard working and very friendly great scientist;
2. I was invited to do research in high energy astrophysics and cosmology even though my previous advisors told me that this is useless science.
This was an extremely lucky step because before the early 60s development of the world of astronomy was relatively slow. But in the middle of the 60s giant discoveries were being made practically every year. Among these great discoveries made during last 50 years were:
1. cosmic microwave background radiation (CMB), filling the whole Universe. Its angular distribution and frequency spectrum carries a lot of information about key properties of the Universe as a whole;
2. quasistellar radio sources (quasars) at cosmological distances. Today we know that these extremely bright sources of radiation in all spectral bands are accreting supermassive black holes in the nuclei of distant galaxies;
3. radio pulsars which occurred to be rapidly rotating, strongly magnetized neutron stars;
4. gamma-ray bursts which for a few seconds appear much brighter in gamma-rays than the whole sky;
5. accreting stellar mass black holes and neutron stars with quasiregular nuclear explosions on their surfaces;
6. exoplanets, which opened the way to a better understanding of the origin and uniqueness of the planets in the Solar System;
7. evidence for the inflation of the Universe at it’s very early stages, and evidence for the existence of dark energy and dark matter, which no one was able yet to detect in the ground based physical labs.
I know personally many observational astronomers, cosmologists and theoretical astrophysicists in different countries on the globe who were actively working on these problems. With their common efforts scientists were able to understand the nature of newly detected phenomena and explain them on the basis of well known physics. But it was even more interesting when theorists were able to predict new effects, and the rapid development of the technology of radiation detectors led to the observations of these predicted events on the sky. Each of these steps confirmed that our understanding of our Universe is correct. In the case of effects proposed by my mentor, Yakov Zel’dovich, and me, it was necessary to wait more than 40 years before such observations became possible and useful for modern cosmology. It’s an incredible feeling to recognize that these predicted traces of the sound waves existing at the early stages of the Universe will continue to be visible on the sky for the next billions of years and there is a great question: will there still be observers on the Earth at that time.
It’s a pity that Yakov Zel’dovich is unable to witness how the South Pole Telescope, Atacama Cosmology Telescope in the driest desert in Chile at an altitude of 5 km, and Planck Surveyor spacecraft report detection of many hundreds of “negative” radio sources in the directions toward clusters of galaxies with hot intercluster gas.
We now know a lot about our Universe and its properties and parameters. Nevertheless, there are many open questions and I hope that at least for the next 20-30 years my science—astrophysics and cosmology—will continue to glow.