Viktor A. Ambartsumian

Russian astrophysicist

• Born: September 18, 1908
• Birthplace: Tiflis, Georgia, Russian Empire (now Tbilisi, Georgia)
• Died: August 12, 1996
• Place of death: Byurakan Observatory, near Yerevan, Armenia

Ambartsumian developed the astrophysics of stars and stellar origins and was instrumental in the theory of gigantic catastrophe formation in galaxies related to the evolution of stars and galaxies. He was the founder of the major school of theoretical astrophysics in the Soviet Union.

Early Life

Viktor A. Ambartsumian (ahm-bahrt-SEW-mee-uhn) was the son of a local teacher of literature. Early in school, he developed a passion for mathematics and physics and became extremely interested in the formation, evolution, and energy generation of stars and other heavenly bodies. Already at age eleven, he wrote two scientific papers: “The New Sixteen-Year Period for Sunspots” and “Description of Nebulae in Connection with the Hypothesis on the Origin of the Universe.” Following his passion for science, he went to the University of Leningrad, from which he was graduated in 1928 with high honors. He performed so well and so amazed his instructors that he was offered a position at the university, where he stayed to teach until 1944. In that year, he went to Yerevan, Soviet Armenia, to become the founder and director of the Byurakan Observatory and its subsequent permanent director.

Life’s Work

Very early in his career at the Byurakan Observatory, Ambartsumian became interested in the physics of stars and nebulas, combined with a general regard for astronomical topics of all characteristics. As a by-product of his work, he became the founder of the school for theoretical astrophysics in the Soviet Union, concentrating much of his time and effort on the cosmogony of stars and galaxies. It was his detailed work on the theory of stellar origins that brought him early recognition, particularly his explanation, derived by both reasoning and mathematics, of how gigantic catastrophic explosions had taken place elsewhere in the universe and how such explosions could take place in, or even be required for, the evolution of stars and galaxies. The idea originated from the work of Walter Baade and Hermann Minkowski, who first identified a radio source of extraordinary violence in the constellation of Cygnus. Baade had first announced that the radio source was associated with what appeared to be a closely connected pair of distant galaxies. In the photographs, it appeared that a gigantic collision was occurring, a supremely colossal event that could account for the extensive radio spectrum being emitted from that particular region of extragalactic space. Baade believed that events such as this catastrophe might even be common enough in the universe to account for the numerous extragalactic radio sources already identified by that time. Ambartsumian, however, in 1955 was able to gather enough evidence, both observational and theoretical, to show that the collision view was undoubtedly wrong. As an alternative, he proposed that vast explosions could occur within the core of a galaxy, creating a tremendous release of energy, somewhat analogous to supernova explosions, only on a galactic, rather than a stellar, scale. Mechanisms for such titanic explosions include chain-reaction supernovas erupting in the densely packed galactic core, interactions of normal matter and antimatter, the possible interactions of stars and interstellar materials with a superheavy black hole, or the total destruction of a galaxy’s nucleus through some other mechanism involving fantastic releases of energy, much more than could ever be derived from simple atomic bomb explosions. The discovery of other galaxies (particularly that by Allan Sandage, who worked with M-82) in the process of definitely exploding has led to Ambartsumian’s hypotheses becoming well established in current astrophysical thought.

In his role as founder of the Soviet school of combined theoretical physics and astronomy, Ambartsumian initiated the study of numerous topics, in some areas virtually inventing, redefining, and mathematically settling the field. He founded the quantitative theory for emissions of light energy from gaseous nebulas, a precursor to his ideas on how stars formed. As a method for forming such gaseous nebulas, he established a detailed synthesis for calculating the masses ejected by stars in their normal, nonstationary state, now called solar wind, and for those far enough along in their life history to become novas or exploding stars. To handle large groups of stars, such as those found in globular clusters of up to one million members, Ambartsumian developed the fundamentals of statistical mechanics as applied to stellar systems. One of the offshoots of that work was his ability to demonstrate that smaller stellar clusters, such as galactic open-star clusters, gradually decay via the loss of individual stars. On that basis, he found he could estimate the ages of the observable clusters in our galaxy.

While working as a scientist, he also performed other functions. From a role as a corresponding member in 1939, be became an academician of the Academy of Sciences of the Soviet Union in 1953, supplementing the position he had already held since 1943 as academician of the Academy of Sciences of Soviet Armenia. He was president of that group in 1947. Also in 1947, he became a professor at the University of Yerevan.

In the late 1940’s, Ambartsumian became proficient in dealing with some fundamental problems of stellar cosmogony. In 1947, he had discovered dynamically unstable systems of a new type, called stellar associations. By studying these extremely young collections of stars, he found that light, traveling through supposedly empty space, was not being absorbed by a continuous distribution of matter in the interstellar space but rather was reduced principally by discrete dark nebulas lying between stars and the observer. He formulated a special mathematical theory for statistical research on these peculiar interstellar absorption dust balls, in the process solving numerous problems with a theory of light-scattering in dense, turbid media. His work saw the formation of stars as collapsing clouds of dust under gravity forming embryonic stars fueled by the infalling hydrogen from the dark nebula surrounding the stellar nursery. A special case he developed was the theory of baryonic stars, stars possessing a density much greater than nuclear density, which was a forerunner of the black hole idea.

Ambartsumian also had a substantial influence on the trend of dealing with the enormous activity found in central galactic areas. He proved that the nuclei of galaxies were indeed responsible for a host of recently discovered phenomena, including colossal explosions greater than anything ever before perceived, ejections of fantastic quantities of materials by both violent and quiescent means, and extremely intense emissions of radio waves, microwaves, and gamma radiation. Ambartsumian’s treatment of these matters has had an impact on the new astronomy that uses the entire electromagnetic spectrum for surveying the universe.

Ambartsumian acted as both vice president (1948-1955) and president (1961-1964) of the International Astronomical Union. He was also a member of many different foreign academies and scientific societies. In 1968, he was elected president of the International Council of Scientific Unions. He was twice awarded the State Prize of the Soviet Union, in 1946 and 1950, was awarded the Order of Lenin on three separate occasions, and received numerous other orders and medals, both within the Soviet Union and from foreign scientific societies.

Significance

Ambartsumian was one of the most visible Soviet astronomers through the early 1980’s, primarily because of his frequent attendance at numerous international scientific meetings. Although he acted as member and president of the Armenian Academy of Sciences, and was a member of the Soviet Union’s Academy of Sciences as a theoretical astrophysicist, he was also an aggressive supporter of observational astronomy. Under his directorship, the Byurakan Observatory rose to the forefront of the astronomical facilities in the Soviet Union. He led the push to develop vast areas of astronomical research in the Soviet Union, including planetary astronomy (particularly studies of Venus), meteorites, and comets; a second major program on stellar astronomy, particularly stellar associations, flare stars, symbiotic stars, and normal stellar phenomena; and, finally, extragalactic astronomy, particularly those Markarian galaxies bright in ultraviolet light, active galaxies, and theoretical galactic studies.

Ambartsumian became a professor at the University of Yerevan in 1947. He became a Hero of Socialist Labor in 1968 for his many contributions in science and government. He particularly enjoyed giving public lectures, extolling an all-union society, Znanya (knowledge), which connects many outstanding scholars with adult education and helps shape policy on the numerous planetariums in the country. He favored the many flourishing academies established throughout the Soviet Union that have helped revive the culture of particular nationalities. He did not see this mixing of astronomy and government as a problem; rather, he saw both areas as part of his own personal search for a succinct view of the universe.

Bibliography

Asimov, Isaac. The Exploding Suns: The Secrets of the Supernovas. New York: E. P. Dutton, 1985. A delightful exploration of the life history of stars, emphasizing their origins and their ultimate fates as bodies destined to explode. Follows the history of various size stars to their ends as planetary nebulas, novas, or supernovas. This book is excellent reading. Well illustrated and designed for general readers.

Mihalas, Dmitri, with Paul McRae Routly. Galactic Astronomy. San Francisco, Calif.: W. H. Freeman, 1968. Deals with all the configurations of a normal galaxy, from stars and their origins to the gaseous contents found between the stars. Traces the evolution of stars and star clusters and discusses energy generation near galactic cores. Heavy reading with an extensive bibliography for references and some mathematics.

Murdin, Paul. The New Astronomy. New York: Thomas Y. Crowell, 1978. Written for general readers, this work deals with the end of stellar evolution, when the catastrophic collapses occur. Tracing the trail of ancient supernovas, the story of the creation of the elements, black holes, and neutron stars is told, ending with the ultimate fate of the universe. Contains line diagrams.

Reddish, V. C. Stellar Formation. Elmsford, N.Y.: Pergamon Press, 1978. A detailed account of how stars form from the condensation of dust and gases found in the nebulas of the galaxy. The evidence for stellar birth is presented clearly; the subsequent evolution is presented in enough detail to show the resultant stages of life for different-sized bodies. Includes extensive mathematics and extra references. College-level physics is necessary for complete understanding.

Shklovskii, I. Stars: Their Birth, Life, and Death. San Francisco, Calif.: W. H. Freeman, 1978. For advanced readers, an excellent summary detailing the origin of stars from dust clouds, their subsequent evolution through middle age, and their ultimate demise based on their original size. Clearly illustrated, with extensive references. Some mathematics.

Weedman, Daniel W. “Making Sense of Active Galaxies.” Science 282, no. 5388 (October 16, 1998). Describes Ambartsumian’s pioneering work in the study of active galactic nuclei (AGN) and the continued study of AGN by astrophysicists at the Byurakan Astrophysical Observatory in Armenia.

Zeilik, Michael, ed. Cool Stars, Stellar Systems, and the Sun. New York: Springer, 1986. A collection of articles presented on star systems under various conditions of size, temperature, and activity. The evolution of lower-temperature stars is discussed, as are the life features of multiple-star collections. The Sun’s history is used for comparison. Contains extensive references and heavy mathematics.

Zeldovich, Ya. B., and I. D. Novikov. Stars and Relativity. Vol. 1. Chicago: University of Chicago Press, 1971. A detailed treatise on the history of stars from their birth to their ultimate evolutionary stage, based on information predicted by the theory of relativity. Deals with exploding bodies, interactions of stars within galaxies, and catastrophes in nature. Extremely detailed in mathematics but possesses a tremendous amount of information.