Viktor AMBARTSUMIAN (1908-1996)

Viktor Amazasp Ambartsumian was born in September 18, 1908, in Tbilisi. After the graduation of the Leningrad (Saint-Petersburg) University and post-graduate studentship in Pulkovo Observatory, he founded in the University the first department of astrophysics in the Soviet Union. In 1943 V.A.Ambartsumian was one of the founding members of the Armenian Academy of Sciences and its vice-president. Soon, in 1947, he became the president of the Academy, and since 1993 he was its honorary president. In 1946 the Byurakan Astrophysical Observatory of the Academy of Sciences of Armenia was founded. Since the first days till 1988 V.A.Ambartsumian was the director and scientific leader of the Byurakan

Observatory. And since 1988 he was its honorary director. Thanks to Ambartsumian’s and his colleagues’ works it became one of the known observatories in the world. Ambartsumian’s works are distinguished in perfection and almost every time opened new directions in astrophysics. His works on physics of gaseous nebulae and radiation transfer theory are classic. They played important role in this field, in particular, in the theory of multiple light scattering. The invariance principle, formulated in these works for the first time, had a wide application in a number of other fields of the science. Ambartsumian’s investigations on the problem of stellar evolution brought in 1947 to revealing of stellar systems of new type - stellar associations. The existence of stellar associations in the Galaxy, dynamically non-stable and disintegrating systems, was the first observational evidence in favour of continuing at present star-formation in it. Ambartsumian put forward a hypothesis about the joint origin of the diffuse matter and stars of dense matter of unknown nature - protostars. Ambartsumian’s studies of early stages of evolution of stars and stellar systems are rather significant. It was shown, that in the early stages of the evolution, the instability of state reveals itself, being the regular phase of the cosmogonic processes. Among these results the conclusions about the existence of stellar systems of positive total energy in the Galaxy, non-thermal nature of ultraviolet stellar radiation of T Tauri type and flare stars, are to be mentioned. New principle results were achieved by V.A.Ambartsumian in study of evolution of galaxies. It was shown for the first time that the central regions of galaxies - their nuclei, play decisive role in the phenomena of instability, observed in galaxies. Besides the stars and diffuse matter they must contain dense massive bodies of unknown nature. The activity of galactic nuclei defines their evolution. At present the active galactic nuclei (AGN) are the most intensively studied objects in extragalactic astronomy. Ambartsumian has carried out some other investigations of great importance in astrophysics as well, such as the study of interstellar absorbing matter in the Galaxy (the idea of its ragged structure, the theory of fluctuations of light of the Milky Way), works on stellar dynamics (establishing of the base of new, statistical mechanics of stellar systems), statistical investigations of flare stars, and others. Ambartsumian was an outstanding organizer of science, who significantly promoted the international scientific cooperation. In 1948-1955 he was the vice-president, and in 1961-64 - the president of the International Astronomical Union (IAU), in 1968 and 1970 he was twice elected the president of the International Council of Scientific Unions (ICSU). His many-sided activity accepted high estimate. He was awarded governmental prizes, orders and medals of a number of countries (Twice Hero of Socialist Labour in 1968 and 1978, USSR State Prizes in 1946 and 1950, Russian State Prize in 1995, National Hero of Armenia in 1994), gold medals of a number of academies and scientific societies. He was elected honorary and foreign member of 28 Academies of Sciences, including USA, UK, France, Italy, Holland, Belgium, Denmark, Sweden, Greece, Czechoslovakia, India, Argentina, and other National Academies, honorary member of scientific societies of many countries, honorary doctor of the Universities of Canberra (Australia), La Plata (Argentina), Warsaw and Torun (Poland), Prague (Czechoslovakia), Liege (Belgium) and Sorbonne (France).V.A.Ambartsumian has published about 20 books and booklets, more than 200 scientific papers, numerous popular articles. Victor A. Ambartsumian passed away in August 12, 1996 in Byurakan. He will remain forever as one of the most outstanding scientists of the XX century.