Eminent Armenian scientist and astronomer, Prof. Victor Ambartsumian (also spelled Ambartsumyan and Ambarsumyan), Honorary President of the Armenian National Academy of Science, died on the 12th of August, 1996. He was an honorary or foreign member of academies of sciences of more than 25 countries and held honorary degrees from many well-known universities. The scientific community recognized his activities by electing him president of the International Council of Scientific Unions (1970–1974). His book Theoretical Astrophysics (1958, Pergamon Press) became a bible for a generation of astronomers.
Ambartsumian was born on 18 September 1908 in Tbilisi, Georgia. He wrote his first papers on “The New Sixteen-Year Period for Sunspots” and “Description of Nebulae in Connection with the Hypothesis on the Origin of the Universe” when he was only an 11-year old schoolboy. His talent was recognized very soon, and his father sent him to Leningrad where be obtained his higher education, receiving a first degree from Leningrad University and carrying out postgraduate studies at Pulkovo Observatory in 1928–1931. His first collaborators and friends were A. Kozyrev, D. Ivanenko, and M. Bronstein. During the short period 1928–30, while still a student, Ambartsumian published 22 papers in Astronomische Nachrichten, Zeitschrift für Physik, MNRAS, and other journals. One of these (Z. Phys. 53, 690, 1929 ) was, in effect, the first paper in the theory of inverse spectral problems associated with the Sturm-Liouville operators.
Ambartsumian had broad research interests from the beginning. His work “The Quantization of Space” was reported at the International Conference in Odessa, where Summerfeld, Pauli, Jordan, Dirac, and many others were present. After the meeting, Pauli told him, “Colleague Ambartsumyan, at the moment the position of quantum electrodynamics appears hopeless. However, in a conversation with Mr. Tamm, I said that just a few ideas are needed like those of the English mathematician Ursell and yours to make the study of quantum mechanics possible again.” In another paper, published in 1930 (when neutrons had not yet been discovered), Ambartsumian and Ivanenko argued against the presence of electrons in atomic nuclei. Soon he became a lecturer at Leningrad State University, and he was made a professor in 1934 at the age of 26. He then organized and headed the department of astrophysics at Leningrad (the first in the Soviet Union). His first PhD student was V. V. Sobolev (known for the Sobolev approximation in radiative transfer). It is commonly accepted that V. A. Ambartsumian was a father of the Soviet school of Theoretical Astrophysics. The most important steps in his scientific career can be given as:
Early papers published in the 1930’s and devoted to radiative transfer and stellar dynamics. After many years Edward A. Milne would write in Observatory that he had never imagined the theory of radiation transfer, on which he too, had been working, could have attained the level of development and beauty which it had achieved in the hands of Ambartsumyan.
First numerical inversion of the Radon transform (MNRAS 96, 172, 1936, communicated to the RAS by Arthur Eddington ). This involved the 3D velocity distribution of stars in the Galaxy. After many years, A. Cormack (Dept. of Physics, Tufts University) would write in this connection: “Even in 1936 computed tomography might have been able to make significant contributions to, say, the diagnosis of tumors in the head … it seems to me quite possible that Ambartsumian’s numerical methods might have made significant contributions to that part of medicine had they been applied in 1936” (Computed Tomography, Some History and Recent Developments, Proc. of Symposia in Applied Mathematics, Vol. 29, p. 35, 1985).
First idea about the patchy structure of interstellar absorption, 1938. S. Chandrasekhar wrote in this connection: “Ambartsumian’s marvelously elegant formulation of the fluctuations in brightness of the Milky Way in the limit of infinite optical depth, showed that the probability distribution of the fluctuations in the brightness of the Milky Way is invariant with the respect to the location of the observer.” Ambartsumian introduced for the first time the now commonly accepted notion that interstellar matter occurs in the form of clouds.
The Principle of Invariance, 1943. The power of this method introduced in a theory of radiation transfer has been applied in other sciences (optics, mathematical physics, etc.) allowing people to handle easily very complex mathematical problems. The method was successfully developed later by S. Chandrasekhar in his book Radiative Transfer.
Discovery of Stellar Associations, 1947. V. Ambartsumian originally introduced the term Stellar Association, dividing them into two groups: OB and T associations. He recognized that they are star forming regions at a time when the whole idea of star formation as an ongoing process was regarded as very speculative. This interpretation of groups of stars with positive total energy, in combination with ideas that can be traced back to his thesis advisor, A. A. Belopolsky, played a role in his eventual interpretation of quasars and other active galaxies as due to explosive expansion from some dense core rather than as accretion-powered sources.
It was in the early 1950’s when Prof. Victor Ambartsumian first raised the issue of Activity of Nuclei of Galaxies (AGN). In his famous report at the Solvay Conference on Physics (Brussels 1958), Armbartsumian said that enormous explosions take place in galactic nuclei and as a result a huge amount of mass is expelled. In addition, if this is so, these galactic nuclei must contain bodies of huge mass and unknown nature. During a break in the session, Walter Baade spoke to Ambartsumian and said: “Prof. Ambartsumian, you have come from the Soviet Union and I from America. Logically speaking, you should be a materialist, and I, an idealist. But what you have said is nothing other than a pure idealism! It’s fantastic! You speak about some kind of ‘non-stellar’ objects which no one has seen. So it must be something inexplicable, mysterious.” The concept of AGN was widely accepted a few years later. One of the students of Ambartsumian, B. Markarian (known for Markarian galaxies) completed a survey of galaxies with UV excess using the 1-m Schmidt telescope of the Byurakan Observatory. IAU Symposium No. 29 and 121 were hosted by the Byurakan Astrophysical Observatory in 1966 and 1986, 10 and 30 years after Ambartsumian’s pioneering ideas about AGNs.
Ambartsumian returned to Armenia from Leningrad, and in 1946 founded the Byurakan Astrophysical Observatory on the slopes of Mt. Aragats (4090 m above sea level), rising from the valley of Mt. Ararat. Soon he became President of the Armenian Academy of Science, serving from 1947 to 1993 and as honorary president thereafter. In 1985, about 20,000 scientists were working in this small republic of fewer than 3.5 million people, most of them in institutions part of the Academy system. Ambartsumian founded the journal Astrofizica (Astrophysics) and remained its editor-in-chief as well as director of Byurakan until the mid 1980’s.
It is generally recognized that Ambartsumian’s papers were very original and revolutionary, striking in their mathematical beauty and accuracy. Congratulating him on his 80th birthday, Chandrasekhar wrote: “The only other astronomer of this century who compares with Academician Ambartsumian in his constancy and devotion to astronomy is Prof. Jan Oort; but they would appear to be dissimilar in every other way. It will be a worthy theme for a historian of science of the 21st century to compare and contrast these two great men of science. He is an astronomer par excellence. There can be no more than two or three astronomers in this century who can look back on a life so worthily devoted to the progress of astronomy.” (Astrofizica 29, 408, 1989; English translation: ).