Viktor Ambartsumian’s most prominent scientific results
(by H.A. Harutyunian and A.M. Mickaelian)


1.For the first time the problem of finding the differential equation corresponding to the known family of eigenvalues was solved. For the time a problem inverse to Sturm-Liuville’s problem was formulated, which later became a starting point to create an entire field of analogical class inverse problems (1929).
  W.A. AmbarzumjanUber eine Frage der Eigenwerttheorie (On a Problem of the Theory of Eigenvalues) // Zeitschrift fur Physik, Vol. 53, Nos. 9-10, p. 690-695, 1929 (in German).

2.An idea that not only the quanta of the electromagnetic field, photons, but also other particles (including particles having nonzero rest mass) may be born and disappear as a result of their interaction with other particles (this idea lays in the basis of modern physics of the elementary particles and quantum field theory) (together with D.D. Ivanenko, 1930).
W.A. Ambarzumjan, D.D. IwanenkoEine quantentheoretische Bemerkung zur einheitlichen Feldtheorie (A Quantum-Theoretical Remark on the Uniform Field Theory) //
Доклады Академии Наук СССР, сер. А (Doklady USSR Acad. Sci., Ser. A), Vol. 3, p. 45-49, 1930 (in German).

3.The impossibility of existence of free electrons in the atomic nuclei was proved. It was shown that only electrically uncharged elementary particles of approximately proton mass could exist together with protons in nuclei. Two years later James Chadwick discovered the neutron (together with D.D. Ivanenko, 1930).
  W.A. Ambarzumjan, D.D. IwanenkoUber eine Folgerung der Diracschen Theorie der Protonen und Elektronen (On a Consequence of the Dirac Theory of Protons and Electrons) //
Доклады Академии Наук СССР, сер. А (Doklady USSR Acad. Sci., Ser. A), Vol. 6, p. 153-155, 1930 (in German).
V.A. Ambartsoumian, D.D. Ivanenko – Les electrons inobservables et les rayons β (The Inobservable Electrons and β Rays) // Compte rendu hebdomadaire des seances de l'Academie des sciences de Paris, Vol. 190, No. 9, p. 582-584, 1930 (in French).

4.For the first time the influence of the light pressure on the planetary nebulae dynamics was studied. The new result on the expansion and dissipation of planetary nebulae owing to light pressure was obtained. It was shown that the age of planetary nebulae could not exceed 100000 years if no continuous outflow existed from the central star. For the first time the new evolutionary paradigm on formation of objects from denser matter was formulated (1932).
  V.A. Ambartsumian – The Radiative Equilibrium of a Planetary Nebula // Monthly Notices of the Royal Astronomical Society (MNRAS), Vol. 93, No. 1, p. 50-61, 1932 (in English).

5.New method (modification of Zanstra’s method) for determination of the planetary nebulae’s central stars surface temperature giving the probabilistic definition of short wave energetic photons transformation into less energetic ones. This definition led to the radiative equilibrium determination (1932). This method bears V. Ambartsumian’s name.
  V.A. AmbartsumianOn the Temperatures of the Nuclei of Planetary Nebulae //
Циркуяр Пулковской Обсерватории (Poulkovo Observatory Circular), No. 4, p. 8-12, 1932 (in English).

6.For the first time the amount of matter and masses of envelopes ejected due to the Novae and Supernovae explosions was estimated. Presently known values of 0.00001 and 1 solar masses for Novae and Supernovae phenomena have been found, respectively (together with N.A. Kozirev, 1933).
  W.A. Ambarzumjan, N.A. KosyrewUber die Massen der von den neuen Sternen ausgestossenen Gashullen (On the Masses of Envelopes thrown out by Novae) // Zeitschrift fur Astrophysik, Vol. 7, No. 4, p. 320-325, 1933 (in German).

7.For the first time the distribution function of stellar 3D velocities has been obtained only using radial velocities and coordinates of stars. This problem has been reduced to the numerical inversion of the Radon transform. Four decades later the same mathematical scheme was applied for the construction and exploitation of computer tomography (1936).
  V.A. Ambartsumian – On the Derivation of the Frequency Function of Space Velocities of the Stars from the Observed Radial Velocities // Monthly Notices of the Royal Astronomical Society (MNRAS), Vol. 96, No. 3, p. 172-179, 1936 (in English).

8.By means of investigation of white stars at low Galactic latitudes, the existence of a great number of white dwarf stars in the Galaxy was shown, which was later proved by discoveries of a large number of white dwarfs (together with G.A. Shain, 1936)
  V.A. Ambartsumian, G.A. Shain – On the Faint White Stars in Low Galactic Latitudes //
Астрономический Журнал (Soviet Astronomy), Vol. 13, No. 1, p. 1-7, 1936 (in English).

9.Using the statistical studies of wide binaries it was shown for the first time that those did not obey the dissociative equilibrium conditions. The same studies allowed to arrive at a conclusion that the components of binaries had been formed jointly. Moreover, the observed distribution put an upper limit for the Galaxy age, 10 billion years. This proved incorrectness of the generally accepted estimate of the age of our Galaxy obtained by James Jeans (so-called "long scale", 1013 years) was shown and a new estimate of its age was given (so-called "short scale") (1936-1937).
  V.A. Ambartsumian – Double Stars and the Cosmogonic Time-Scale // Nature, Vol. 137, No. 3465, p. 537, 1936 (in English).
В.А. Амбарцумян К статистике двойных звезд (On the Statistics of Double Stars) // Астрономический Журнал (Astron. Zh.), Vol. 14, No. 3, p. 207-219, 1937 (in Russian).

10.Principles of statistical mechanics of stellar systems. The mechanism of star “evaporation” from the open stellar clusters was revealed. Using of this effect allowed to find for the first time the halftime of disintegration of the clusters, and was applied to anticipate the gradual decrease of the number of low mass stars in clusters. It was proven that open star clusters disintegrate during about 1 billion years, and predict the process of impoverishment of the clusters with dwarf stars. These studies provided a theoretical base for decreasing the accepted age of the Galaxy for a thousand times and for introducing “the short scale” of the Galaxy age (1938).
В.А. Амбарцумян К вопросу о динамике открытых скоплений (On the Dynamics of Open Clusters) // Труды АО ЛГУ; Уч. зап. ЛГУ, Серия мат. наук (Астрономия), вып. 4 (Trudy LGU; Ucheniye Zapiski LGU, Ser. Math. Sciences (Astronomy). Issue 4), No. 22, p. 19-22, 1938 (in Russian).

11.The nature and patchy structure of the interstellar absorbing matter (dust component of the Milky Way) was revealed and the mean absorption of individual clouds was estimated to be equal to 0.2 magnitudes (together with Sh.G. Gordeladze, 1938).
  V.A. Ambartsumian, Sh.G. Gordeladze – Problem of Diffuse Nebulae and Cosmic Absorption //
Бюллетень Абастуманской АО (Bulletin of the Abastumani Astrophysical Observatory), No. 2, p. 37-68, 1938 (in English and Georgian).

12.Development of light scattering theory in turbid medium, theory of Invariance. The Invariance principle was proposed for solving the radiative transfer problems. A very simple physical reasoning that the reflection properties of the semi-infinite plane-parallel medium do not change if a very thin layer of the same physical properties is added to its boundary gave an excellent base for creation of a new research method (1941-1942). This principle bears V. Ambartsumian’s name and the corresponding function was named V. Ambartsumian’s φ function.
В.А. Амбарцумян Новый способ расчета рассеяния света в мутной среде (A New Method of Calculation of the Light Scattering in Turbid Medium) // Известия АН СССР, серия географическая и геофизическая (Izvestiya Acad. Sci. USSR, Ser. Geograph. and Geophys. Sci.), Vol. 3, p. 97-103, 1942 (in Russian).
V.A. AmbartsumianThe Scattering of Light in a Turbid Medium // Journal of Physics, Vol. 5, No. 1, p. 93, 1941 (in English).

13.The theory of the fluctuations in brightness of the Milky Way was formulated. In the simplest form it asserts that the probability distribution of fluctuations in the brightness of the Milky Way is invariant to the location of the observer (1944).
В.А. Амбарцумян К теории флюктуации яркости Млечного Пути (To the Theory of Fluctuation in the Brightness of the Milky Way) // Доклады Академии Наук СССР (Doklady USSR Acad. Sci.), Vol. 44, No. 6, p. 244-247, 1944 (in Russian).

14.Discovery of stellar associations, groups of hot giants and T Tauri stars. It was shown for the first time that the star formation process continues at all stages of the evolution of our Galaxy, including the present one and that the star formation is a permanent process. A conclusion was drawn that stars are formed not individually, but in groups (1947).
  Evolution of Stars and Astrophysics // Acad. Sci. ArmSSR, 39 p., Yerevan, 1948 (in Armenian).
В.А. Амбарцумян Предварительные данные об О-ассоциациях в Галактике (Preliminary Data on O-Associations in the Galaxy) // Доклады Академии Наук СССР (Doklady USSR Acad. Sci.), Vol. 68, No. 1, p. 21-22, 1949 (in Russian).

15.Theoretical prediction of the phenomenon of expansion of stellar associations. Revealing the importance of the stellar associations as dynamically unstable entities. Statistics of the Trapezium Orionis type systems and a proof of disintegration of the young stellar systems (together with B.E. Markarian, 1949-1951).
В.А. Амбарцумян Звездные ассоциации (Stellar Associations) // Астрономический Журнал (Astron. Zh.), Vol. 26, No. 1, p. 3-9, 1949 (in Russian).
В.А. Амбарцумян, Б.Е. Маркарян (V.A. Ambartsumian, B.E. Markarian) – Звездная ассоциация вокруг Р Лебедя (Stellar Association around P Cygni) // Сообщения Бюраканской обсерватории (Communications of the Byurakan Observatory), No. 2, p. 3-17, 1949 (in Russian).
В.А. Амбарцумян О вероятности кажущихся кратных систем типа Трапеции Ориона (On the Frequency of the Orion Trapezium type Apparent Multiple Systems) // Доклады Академии Наук АрмССР (Doklady Acad. Sci. ArmSSR), Vol. 13, No. 4, p. 97-103, 1951 (in Russian).
В.А. Амбарцумян К статистике кратных систем типа Трапеции (On the Statistics of Trapezium type Multiple Systems) // Доклады Академии Наук АрмССР (Doklady Acad. Sci. ArmSSR), Vol. 13, No. 5, p. 129-131, 1951 (in Russian).

16.Showed the nonthermal nature of the continuous emission observed in the spectra of non-stable stars and put forward an idea about new possible sources of stellar energy, the hypothesis of the superdense protostellar matter (1954). This hypothesis bears V. Ambartsumian’s name.
В.А. Амбарцумян Явление непрерывной эмиссии и источники звездной энергии (The Phenomenon of the Continuous Emission and Sources of Stellar Energy) // Сообщения Бюраканской обсерватории (Communications of the Byurakan Observatory), No. 13, p. 1-36, 1954 (in Russian).

17.The hypothesis on the activity of galactic nuclei was proclaimed. The various forms of activity were presented as different manifestations of the same phenomenon of activity. The evolutionary significance of the activity in the galactic nuclei was emphasized and a further hypothesis was suggested on the ejection of new galaxies from the active galactic nuclei. The hypothesis on the superdense protostellar matter was engaged to explain the observational data (1956). This hypothesis bears V. Ambartsumian’s name.
В.А. Амбарцумян К вопросу о природе источников радиоизлучения (On the Nature of Radio Sources) // Труды Пятого совещания по вопросам космогонии: "Радиоастрономия", 9-12 марта 1955 г., АН СССР (Proc. Fifth conference on Problems of Cosmogony: "Radioastronomy", held on 9-12 Mar 1955. Acad. Sci. USSR), p. 413-416, Москва (Moscow), 1956 (in Russian).
В.А. Амбарцумян О кратных галактиках (On Multiple Galaxies) // Известия АН АрмССР, серия физико-математических, естественных и технических наук (Izvestiya Acad. Sci. ArmSSR, Ser. Phys.-Math., Nat. and Tech. Sci.), Vol. 9, No. 1, p. 23-43, 1956 (in Russian).

18.Theoretical studies of the hypothetical superdense degenerate protostellar matter: development of principles of the theory of baryonic stars, which allowed a detailed research of physical conditions in superdense stellar conditions in the frame enabled by the modern knowledge of physics. These researches later on allowed increasing the Chandrasekhar limit of stellar masses (together with G.S. Saakyan, 1960-1961).
В.А. Амбарцумян, Г.С. Саакян (V.A. Ambartsumian, G.S. Saakyan) О вырожденном сверхплотном газе элементарных частиц (The Degenerate Superdense Gas of Elementary Particles) // Астрономический Журнал (Astron. Zh.), Vol. 37, No. 2, p. 193-209, 1960 (in Russian) // English translation in: Soviet Astronomy, Vol. 4, No. 2, p. 187-201, 1960.
В.А. Амбарцумян, Г.С. Саакян (V.A. Ambartsumian, G.S. Saakyan) О равновесных конфигурациях сверхплотных вырожденных газовых масс (On Equilibrium Configurations of Superdense Degenerate Gas Masses) // Астрономический Журнал (Astron. Zh.), Vol. 38, No. 5, p. 785-797, 1961 (in Russian) // English transaltion in: Soviet Astronomy, Vol. 5, No. 5, p. 601-610, 1962.
В.А. Амбарцумян, Г.С. Саакян (V.A. Ambartsumian, G.S. Saakyan) – Внутренное строение гиперонных конфигураций звёздных масс (Internal Structure of Hyperon Configurations of Stellar Masses) // Астрономический Журнал (Astron. Zh.), Vol. 38, No. 6, p. 1016-1024, 1961 (in Russian) // English transaltion in: Soviet Astronomy, Vol. 5, No. 6, p. 779-784, 1962.

19.Statistical studies of the flare stars revealed their evolutionary status: a method for estimation of the total number of flare stars in a star system based on the number of the observed flares. The flare activity was shown to be the regular stage in the evolutionary path of the low luminosity and low mass late-type stars. It was proved that all the stars of the mentioned category necessarily pass through the stage of flare activity in the early phases of their evolution (1968).
В.А. Амбарцумян К статистике вспыхивающих объектов (On the Statistics of Flare Objects) // Труды симпозиума "Звезды. Туманности. Галактики", посвященного 60-летию академика В.А. Амбарцумяна, Бюракан, 16-19 сентября 1968 г., АН АрмССР (Proc. symp. "Stars, Nebulae, Galaxies", devoted to the 60th anniversary of academician V.A. Ambartsumian, held in Byurakan, 16-19 Sep 1968. Acad. Sci. ArmSSR), p. 283-292, Ереван (Yerevan), 1969 (in Russian).

20.Obtaining an original solution of the inverse problem of derivation of the distribution function of average frequencies of flares in the given stellar system on the basis of chronology of discovery (first flares) and confirmation (second flares) of the flare stars (1978).
В.А. Амбарцумян Вывод распределения частоты звёздных вспышек в звёздном агрегате (Derivation of the frequency function of stellar flares in a star cluster) // Астрофизика (Astrofizika), Vol. 14, No. 3, p. 367-381, 1978 (in Russian) // English translation in: Astrophysics, Vol. 14, No. 3, p. 209-217, 1978.