The importance of theoretical researches is very great for the development of exact sciences. Theoretically interpreting the results of experimental or observational works, in some cases they predict new physical phenomena and by that predetermine the way of further research in the given direction. In this way the most interesting and important successes of modern science have been reached. By the role played by them and the significance in science, theoretical researches can be divided into two groups. The overwhelming majority of them, researches of the first group, are born on the basis of understandings received a general recognition and corresponding to scientific level of the time. These researches, playing a positive role in partial extension of the existing understandings, in the solution of these or that private questions, with a time, after the appearance of closer to the truth understandings, gradually give way to researches of new generation.
There are, however, theoretical researches of other kind, the second group, which usually contain absolutely new, contradicting the accepted at that time in science understandings, “crazy” ideas and bold predictions. These new ideas happen to be so unusual that seem unnatural and for this reason they at once meet negative attitude in scientific circles and face strong resistance. Even great scientists of the time not always appear to be ready to agree with the new understandings contradicting the standard. Nevertheless, these new ideas having revolutionary value pass test with the time; the development of experimental (in astrophysics: observational) technology results new and new evidences in favour of new ideas and they strongly enter into the science treasury. Thanks to this, our knowledge of the material world surrounding us extends and goes deep. Just these, incomparably rarely met researches create new scientific directions and open possibilities for further development of science.
Ambartsumian’s works in their majority belong to the second group of researches.
The scientific credo of the scientist is enclosed in the following definition of the limits of scope and possibilities of astrophysics: “Astrophysics is a part of exact natural sciences studying the huge, unimaginable world. Though the human thought is mighty, anyway it is not able to recreate deductively the laws of development of the nature based only on arguments. Therefore the astrophysics is an observational science, leaning completely on the facts obtained from observations. But at the same time it is an exact science, based on mathematical reduction of observations and on mathematical conclusions from them. Meanwhile it uses the known laws of physics”.
For his researches, a new, original approach to the solution of problems is characteristic. The scientist considers as a necessary condition for the solution of each new problem its many-sided studying from the physical point of view. Only later, when on the basis of the actual data the essence of the phenomenon is found out, he starts revealing of the nature of the phenomenon, its theoretical, mathematical treatment. In other words, he puts a basic emphasis on the physical side of the discussed problem, considering the mathematical apparatus as necessary and extremely important, however only auxiliary means of research. Still during the first period of his scientific activity, he wrote that in works of many representatives of theoretical astrophysics “the ardour to the mathematical problems arising at the solution of this or that question is notable, and there is no efficient discussion of those basic physical assumptions which the given theory is based on”.
In his researches Ambartsumian developed and consistently applied three basic principles-approaches, which in many respects helped him in the achievement of fundamental results.
The first of them Ambartsumian developed still in days of youth in connection with the solution of the Storm-Liuville inverse problem. The essence of this approach is enclosed in the point that the actual data (experimental or observational) are used not for confirmation of this or that theoretical model of the phenomenon, but directly for finding-out of the nature of the phenomenon itself. In other words, it is a question of solution of an inverse problem.
Let’s consider Kepler’s and Gauss’ approaches to the problem of determination of orbits of the planets around the Sun noted by Ambartsumian as a characteristic example of application of the two existing approaches to the astronomical phenomena (construction of models and solution of the inverse problem).
Considering, that a planet around the Sun is rotating by an elliptic orbit, Kepler preliminarily calculated the planet’s position in the sky at various moments, and then, comparing these expected positions to the observed ones, by means of consecutive approximations (by the method of tests) defined the elements of the real ellipse, planetary orbits. Gauss also considered that the rotation of a planet round the Sun is made on an elliptic orbit. However, unlike Kepler, for definition of elements of an orbit of a planet, he solved an inverse problem: expressed these elements by the observable positions (coordinates) of the planet. It allowed him to define any planetary elliptic orbit (the elements of the orbit) by direct observation of the planet on arbitrarily chosen three positions in the sky.
Certainly, Kepler, who opened the laws of planetary motions, played more important role in the history of astronomy than Gauss, however the mentioned example gives a clear understanding about serious advantage of the approach based on solutions of inverse problems.
This advantage with success was used by Ambartsumian for the solution, beside the already noted Storm-Liuville inverse problem, of several important problems: the definition of distribution of spatial velocities of the stars from distribution of their observable radial velocities (1936), estimations of the total number of flare stars in a given stellar system on the basis of observations of flare stars already known in this system (1968), and the derivation of the distribution function of average frequencies of flares in a stellar system with the help of chronologies of the first and second flares of stars (1978).
The second principle, widely used by Ambartsumian in his studies, is the developed by him principle of invariance. This principle allowed for definition of parameters of the radiation field in the scattering medium to consider the light scattering events only on border of the medium, not investigating more difficult processes of scattering occurring in the medium itself. The applications of the principle of invariance, in sense various principles of invariance, resulted not only in creation of a new original theory of multiple scattering of light, but also to numerous important results in various fields of modern science.
The third principle developed by Ambartsumian, which underlies practically all his researches devoted to the questions of evolution of stars and galaxies also appeared to be very fruitful.
According to this principle, the modern state of a space object and the direction of changes of this state give a possibility to find such facts that give evidence of the evolution of this object, and finally revealing the way of its development. And the direction of the changes taking place at the given state of a space object is defined rather easily and, that is the most important, without additional assumptions.
Discovery of the non-stationary phenomena in stars and galaxies and interpretation of their crucial importance in the origin and evolution of these space formations (stellar associations, activity of galactic nuclei) are brilliant examples of application of this principle.
This original approach and the outstanding results received with its application were meant by the President of the USSR Academy of Sciences, academician A.P. Aleksandrov when he wrote: “The largest observational and theoretical achievements in modern astrophysics, stellar astronomy and cosmogony are connected with V.A. Ambartsumian's name. V.A. Ambartsumian's theoretical researches quite often went beyond astronomy and astrophysics... He is not only one of the greatest, but is also an extremely original researcher”.
Thanks to the original approach to the problems in point, the deep versatile analysis and generalization of the actual data about stars and stellar systems, Ambartsumian managed to predict new phenomena yet of unknown nature, which at the beginning, almost in all cases, met a skeptical relation of the majority of experts. However after the confirmation by the subsequent researches they caused surprise and admiration.
For example, in 1949 Ambartsumian, analyzing observational data on the distribution of stars in stellar associations and based on proved by him understanding of the dynamic instability of these systems, theoretically predicted the phenomenon of expansion of stellar associations. This prediction was accepted with obvious skepticism.
However just in three years, in 1952, the known Dutch astronomer, former President of the International Astronomical Union, Adrian Blaauw, brilliantly confirmed this prediction, showing that the apparent motions of stars of one of the nearest stellar associations indicate on the expansion of this young system. A bit later, data confirming expansion of some other nearest stellar associations were published. A detailed investigation of the problem based on the study of radial velocities of the stellar associations gave additional confirmation in favour of expansion of stellar associations.
For the last half of the century, it is difficult to find in the history of astronomy a more surprising example of theoretical prediction of a before absolutely unknown phenomenon, which then so successfully proved to be true by observations. The point is that the prediction of the expansion of stellar associations concerns the motions of stars of absolutely new type (expansion and disintegration of stellar systems), which both by their nature and for the reasons giving rise to such motion sharply differ from all that was studied before in stellar astronomy in general and in stellar dynamics in particular. It was natural that this prediction caused in due times a skeptical attitude by astronomers. And it is not difficult to imagine, what stunning impression made among experts the first observational proof of expansion and disintegration of the stellar associations, received by Blaauw.
At the beginning with a big doubt, and from many experts even with a hostile reception, new idea on activity of galactic nuclei was met, too. When in 1958 at the Solvay conference, for the first time Ambartsumian gave a detailed statement of his sights at the evolution of galaxies based on idea about the activity of their nuclei playing a major role in the origin and evolution of galaxies and their systems, this idea was given a very cold reception, at least with mistrust. Since then within 15 years, speaking by Ambartsumian’s words... “Nobody believed in existence of such activity, however today almost everywhere they speak about it”.
Already in 1967 in Prague, at the next General Assembly of the International Astronomical Union (IAU), the experts especially underlined the great importance of the fruitful idea on activity of galactic nuclei and the new scientific direction appeared in astronomy on the basis of this idea.
The newspaper “Nuncio Sidåreo” (“Star messenger”), published during the days of this General Assembly, the statement of the report by the known American astronomer Alan Sandage devoted to radio galaxies and quasars, printed in one of its issues under the following remarkable title: “Doctor Sandage underlined the magnificent prediction of Academician Ambartsumian that remarkably proves to be true by the last observations”.
This “confession” is notable as Sandage who at the beginning skeptically concerned the idea on activity of galactic nuclei, together with another American astronomer Roger Lynds, on the basis of observations carried out by means of the largest 5m telescope of the Palomar Observatory (USA), showed that in the nucleus of the galaxy Ì82, some 1.5 million years ago there was a powerful explosion resulting in an outburst of a gas matter with a mass of some 5 million Solar masses, which now leaves away from the nucleus with a speed of more than 1000 kilometers per second. This surprising result was a brilliant confirmation of the new understanding on activity of the galactic nuclei.
The idea on the activity of galactic nuclei after numerous confirmations by means of observations, entered into science so thoroughly that some astronomers try now to “forget” the decisive role of Ambartsumian’s studies of this question.
Thereupon Sandage’s words deserve a mention, told by him in a report at plenary session of the International Astronomical Union in Prague: “Ambartsumian’s name was not mentioned anywhere in this report. He predicted much of this that here was told. Ten years ago he started to underline the role of nuclei of galaxies. Consistently, at Solvay conference, at the IAU General Assembly in Berkeley and at numerous symposia, at the beginning almost alone he declared that in galactic nuclei there were powerful processes and that astronomers should completely consider them. The realisation of his program only begins now. No any astronomer will deny today that really a mystery surrounds the nuclei of galaxies, and Victor Ambartsumian was the first who realised, what generous award contains in this treasury”.
From the point of view of an estimation of Ambartsumian’s studies about the role of activity of galactic nuclei in evolution of galaxies and their systems and about stellar associations, the centres of star-formation in the Galaxy, the following fact is notable.
In 1967, the journal “Techniques for Youth” addressed to a number of known foreign scientists with the request to answer questions of the anniversary questionnaire made in connection with the 50th anniversary of October revolution. To the question: “What was, to your opinion, the most important contribution made by the Soviet scientists in the field of science that you are engaged?”, the glorified Dutch astronomer, the former president of the International Astronomical Union, foreign member of the USSR Academy of Sciences, Jan Oort has answered: “In my opinion, the most important contribution of the Soviet scientists to astronomy is represented by academician V.A. Ambartsumian’s studies on the role of nuclei of galaxies in their evolution. Ambartsumian the first has paid attention to the mysterious nature of these nuclei. He has mentioned how much it is important for understanding of some phenomena observed in galaxies. The subsequent discoveries have enough clearly shown that the intuitive guess of the Soviet scientist was correct. His ideas concerning the birth of stars in expanding stellar associations are so important as well. This rather original hypothesis has been completely confirmed subsequently by observations”.
Oort’s answer is remarkable not only from the point of view of an appreciation of the scientist’s merits, but also because Ambartsumian’s outstanding scientific contribution even to Oort is represented as a result of “deep intuition and prophetical guesses”.
At all not denying the role of deep scientific intuition in Ambartsumian’s research, it is necessary to note that the secret of personally his as well as the created by him scientific school’s brilliant successes are not in intuitive guesses, even if they are prophetical. Here Ambartsumian’s original approach to the solution of scientific problems is important and decisive. As it was already stated, it consists in the many-sided, deep analysis and generalization and accurate interpretation of the actual data on a considered problem and on this basis a theoretical explanation of the reasons and origins of the observable phenomena. According to Ambartsumian, these two stages of research are obligatory for the achievement of a correct theoretical explanation of the unusual phenomena observed in the Universe.
This feature of researches by both Ambartsumian and his school was noticed also by some foreign scientists. For example, the known American astronomer Halton Arp, in connection with Ambartsumian’s works on activity of galactic nuclei, wrote: “what seems a brilliant intuition concerning the eruptions from galaxies, the role of the nuclei, stellar associations, spiral arms, blue objects and quasars, actually is a result of a discussion of the problem with a big generality and, most of all, its accurate judgement, together with a visual review and investigation of the real shapes of a very big number of galaxies”.
The chairman of the Astronomical Council of the USSR, the corresponding member of the USSR Academy of Sciences, E.R. Mustel meant this feature of Ambartsumian’s researches when he wrote: “Academician V.A. Ambartsumian’s image is an image of an outstanding researcher who on the basis of a deep analysis of already available facts predicts and formulates those laws that these facts explain. In the course of cognition of the nature Victor Amazaspovich acts as an outstanding astrophysicist, physicist, and mathematician”.
The extreme depth of judgements, originality, purposefulness and amazing clearness were always typical to Ambartsumian’s researches.
It is also necessary to underline the consistency that the scientist shows in the approach to the most crucial scientific problems before it is possible to obtain their essentially important solutions. Sometimes he needed along with current scientific works for long years to think about possible ways of solution of remaining still unclear questions of the given problem. Such consistency in scientific work always led to desirable results. The light scattering theory is an example. As it was already noted, in 1943 Ambartsumian succeeded to receive by means of the principle of invariance the exact solution of the problem of the light scattering in the opaque medium. For a long time it seemed that this fine method was inapplicable in the nonlinear theory of light scattering, i. e. in the case when optical properties of the medium vary under the influence of the light passing through this medium. However, the scientist almost after 20 years again returned to this question and, surprisingly for the experts systematically engaged in light scattering problems, gave a very witty method of application of the principle of invariance in problems of the nonlinear theory of light scattering, by means of which he managed to obtain the solution of some nonlinear problems.
It was above noted that the principle of invariance had wide applications in different areas of modern science. Here two more opinions are relevant.
“Ambartsumian’s ideas are very fruitful... Ambartsumian’s “Principles of invariance”, developed further, lead to the theory of invariant embedding. It is a very powerful method in the mathematical physics and the analysis”, – the eminent American mathematician Richard Bellman writes.
In relation with the application of the principle of invariance to the theory of electromagnetic waves propagation, the known American physicist, foreign member of the Academy of Sciences of the Armenian Soviet Socialist Republic, Charles Hrach Papas writes: “Ambartsumian’s principle of invariance is the key for the solution of the problem of electromagnetic waves propagation in periodic and quasi periodic structures. Without the aid of this key the problem would be completely inaccessible”.
Each of Ambartsumian’s work is devoted to the solution of a particular, strictly certain problem. The set of these problems in various areas of researches almost always led to key problems of modern science. In particular, it is the reason that they have made such great impact on development of many areas of astrophysics and astronomy, have created new directions in the science. About the important scientific value of Ambartsumian’s works tells the fact that many of them have been translated to foreign languages and the basic results of these works were included into monographs, books, and textbooks on astronomy and astrophysics.
Now it is difficult to find any issue of periodicals on astrophysics and astronomy where the results of Ambartsumian’s researches are not used. Many of them became classical and are often given without bibliographic references.
About Ambartsumian’s fundamental contribution to modern science about the Universe indicates the fact that his basic works on stellar associations and on activity of galactic nuclei were included into the two-volume book “Primary sources of the XX century astronomy” published in the USA.
Ambartsumian’s some ideas had revolutionary significance in modern science and have completely changed our understandings about the Universe. The following fact is remarkable from this point of view.
In 1973, the USA National Academy of Sciences in connection with Copernicus’ 500-years birthday published a collection “Copernicus’ Heritage” devoted to this anniversary where articles on the most important discoveries made in different areas of natural sciences having revolutionary importance were included. The article of known Polish astronomer Vladimir Zonn devoted to the explosive phenomena taking place in galaxies was included in this collection. Ambartsumian’s ideas on activity of galactic nuclei are stated in it. The compiler and the editor of the collection, the outstanding American mathematician Jersey Neumann sent a copy of the book to Byurakan with the following dedication: “to dear Victor Ambartsumian, the Copernican revolutionary”. The brought to perfection original methods of research developed by Ambartsumian, occupy now a worthy place in the treasury of new methods of modern science and are widely applied to investigation of various phenomena taking place in the Universe.
Ambartsumian is the founder of the theoretical astrophysics school in the Soviet Union and its recognised leader. By now many years he supervises over the as a whole coordination of researches on astrophysics in our country. And it is his big merit that the Soviet astronomers by their researches have brought a considerable contribution to many areas of world astronomy and astrophysics.
In 1947, Ambartsumian was elected an honorary member of the American Astronomical Society. Reporting on that, then president of the society, the greatest American astronomer-theorist, nowadays a Nobel Prize winner Subrahmanian Chandrasekhar wrote: “It is the most appreciation, which the American Astronomical Society can give, and I can tell that the circumstance that your remarkable work thus has been recognized gives to me a satisfaction. Your brilliant ideas always have brought an admiration to me and I am glad that they are recognized everywhere”.
And the American journal “Popular Astronomy” characterized then the scientist by the following words: “Ambartsumian, the honorary member of the American Astronomical Society, is one of the nowadays living greatest astronomers. His insight in the physics is exceptional. He has made a big impact on work of other astronomers of the world”.
Almost in thirty years after those events Chandrasekhar wrote: “Together with all astronomers I am admired by paramount contributions of Ambartsumian to astronomy for the last fifty years, which were continuous, original and brilliant”.
The big influence of Ambartsumian’s ideas on development of various fields of astronomy has repeatedly been noted by outstanding representatives of science.
In the foreword to the book “Evolution of Stars”, one of the greatest astronomers of the XX century, American scientist Otto Struve notes that the theoretical part of this book was under the influence of Ambartsumian’s work “Evolution of Stars and Astrophysics”.
In an article devoted to results of the Moscow General Assembly of the International Astronomical Union in 1958, Jan Oort, marking its great success, wrote: “From the theoretical part for us one more stimulus was the fresh originality of the ideas developed by the Soviet scientists, in particular the academician V. Ambartsumian, ideas that already had inspiring influence”.
The distinguished Mexican scientist, director of the National Observatory in Tonantzintla, Guillermo Haro has noted: “I am interested in the research work conducted in Byurakan because it is based on ideas of academician V. Ambartsumian”.
The known Soviet astronomer, director of the Crimean Astrophysical Observatory of the USSR Academy of Sciences, academician Andrey Severny wrote: “One of the basic problems of modern natural sciences is the problem of the origin and evolution of stars, and, mentioning it, it is impossible to hold back the fundamental contribution to its solution which have brought Victor Amazaspovich Ambartsumian and the headed by him staff of the Byurakan Observatory of the Academy of Sciences of the Armenian Soviet Socialist Republic. All new ideas of the last time concerning the problem of the origin and evolution of stars and stellar systems, as a matter of fact, were left by this observatory... V. Ambartsumian’s all works are typical by the fact that they contain new ideas having deep physical sense”.
About the new understanding concerning the proceeding star-formation process in the Galaxy put forward and proved by Ambartsumian, the well-known American astronomer, the director of the National Kitt-Peak Observatory (USA) Nicolas Mayoll wrote in 1960 on occasion with V.A. Ambartsumian's awarding a gold medal of the Astronomical Society of the Pacific: “This understanding turned to be invaluable in our diligence to understand the processes of the origin and evolution of stars. Ambartsumian’s work in this attractive area, undoubtedly, was one of the most powerful influences in stimulation of modern researches on the stellar evolution and the Galactic structure”.
Meaning these researches, the known Soviet astrophysicist, the corresponding member of the USSR Academy of Sciences, Oleg Melnikov wrote: “For the first time V.A. Ambartsumian has found ways of research of processes of the origin and evolution of stars”.
In an article devoted to the fifty years path of the development of the stellar astronomy in the Soviet Union, the prominent Soviet astronomer, director of the Abastumani Astrophysical Observatory, nowadays also the president of the Academy of Sciences of the Georgian Soviet Socialist Republic, academician Evgeny Kharadze has given the following characteristic to results, as he said “essential and fundamentally important”, received by V.A. Ambartsumian on the basis of the study of stellar associations: “It was an event that caused such a stream of searches, stimulated the observations in such a way that it is difficult to note at all any other example in the Soviet stellar astronomy, which would leave the same deep and wide trace in the development of this science”.
Later, on another occasion, he wrote: “He (V.A. Ambartsumian, L.Ì.) came to essentially new, important conclusions at studying of problems of evolution of stars and galaxies: he formulated qualitatively new concepts and began new directions in galactic and metagalactic researches”. We have already noted that Ambartsumian in the Leningrad period of his activity has brought certain contribution to some fields of modern mathematics and physics that has led to his recognition in the circle of experts. The following, characteristic for the scientist example indicates on this. In 1950 in Stockholm, Ambartsumian got acquainted with a Swedish professor of mathematics. Naturally, he introduced himself as a professor of astrophysics. The Swedish professor took an interest in, whether he was the relative of mathematician Ambartsumian, mentioning the known work of the latter. The point was Ambartsumian’s work related to the theory of Eigen values of the differential equations (about the problem contrary to the Storm-Liuville problem). It was a great surprise for the Swedish professor when he learnt that the mathematician, the author of the mentioned research, and the professor of astrophysics, Ambartsumian were the same person.
It is necessary to note one more aspect of Ambartsumian’s scientific activity.
His performances, scientific communications, and reports at General Assemblies and Symposia of the International Astronomical Union, at the international scientific conferences and meetings, at universities and observatories of the Soviet Union and other countries (Australia, Austria, Argentina, Belgium, Bulgaria, Hungary, GDR, Holland, Greece, India, Italy, Mexico, Finland, France, Germany, Switzerland, Czechoslovakia), as well as his popular lectures in various cities of the Soviet Union and foreign countries, in particular for the Armenian communities abroad, always promoted the international scientific cooperation, the increase of authority of our domestic science, helped friendship strengthening between the people.
Especially it is necessary to note his basic reports at the General Assemblies of the International Astronomical Union (“About clumpy structure of the interstellar absorbing layer”, Zurich, 1948; “An introductory report on a symposium devoted to evolution of stars”, Rome, 1952; “Problems of extragalactic studies”, Berkeley, USA, 1961), and Solvay conferences (“On the evolution of galaxies”, Brussels, 1958 and “On the nuclei of galaxies and their activity”, Brussels, 1964).
These reports, according to the evidence of the foreign press, were significant events at the mentioned scientific meetings and were in the centre of attention of their participants, known astronomers and physicists.
One of Ambartsumian’s students, the prominent Soviet astrophysicist, academician Victor Sobolev who about 40 years manages the founded by Ambartsumian Chair of Astrophysics of the Leningrad University, more than quarter of century ago characterized his teacher this way: “The stellar sky puts forward many mysteries for the mankind. The astronomy, the science about the structure, motion and evolution of the heavenly bodies, is difficult. Only the few are able to reach the tops of this science and, surveying the opened horizons, to devote new truths to the world. To the number of these few Victor Amazaspovich Ambartsumian, the greatest astrophysicist of our country belongs”.
Already more than half a century academician Victor Ambartsumian by his original researches devoted to key problems of modern science, the discovery of which have enriched the gold fund of the world science, sparkles in the sky of science as a first magnitude star, “as a red supergiant”, according to an image-bearing expression of the pro-rector of the Australian National University in Canberra professor Haksly.
Ambartsumian is a great optimist in science, he trusts in infinite possibilities of science, in particular, of the science about the Universe.
In 1967, in the speech made in Karlov University (Prague) at official ceremony of awarding to him an Honourable doctor diploma, Ambartsumian told: “We live nowadays during an epoch of greatest astronomical discoveries and by the way such discoveries that reveal essentially new phenomena..., an epoch approaches when the astronomy again becomes a source of new ideas and basic changes in physics”. In the first part of his speech V.A. Ambartsumian noted that in XVII century “the astronomical discoveries allowed Galilee and Newton to create the bases of the classical mechanics making at that time an essential part of physics, i. e. to put a basis for the exact natural science”.
The researches by Ambartsumian and his scientific School in many respects promoted the approach of this new stage of development of astronomy. We may hope that so will be henceforth as well.