Ambartsumian’ s view on astronomy of XX century

«Instability phenomena in systems of galaxies,»

«On the nuclei of galaxies and their activity,»

«Problems of extragalactic research,» Invited Discourse at the Gen eral Assembly of IAU.

«Galaxies and their nuclei «.

«Introduction to Nuclei of Galaxies».

The galaxies and their systems. The activity of the galactic nuclei

From the L.V.Mirzoyan’ s book «V. A. Ambartsumian»

The logical continuation of the research of the non-stable phenomena of the stars and their systems was the research of the non-stationary phenomena in the galaxies and their systems on a much more powerful scale and of very unusual nature.

The initial assumption followed by this research, was that in the world of the galaxies manifestations of the non-stationary phenomena connected to the formation of the new structural components should be more powerful and long compared to those occurring among the stars. This assumption was fully proved by the research of Ambartsumian.

He found that the most typical feature of the galaxies spatial distribution is their tendency to appear in physical groups: the multiple galaxies, the galaxy clusters etc.It was made clear for example that the relative number of the multiple systems among the galaxies is greater than among the stars.

Ambartsumians research revealed a remarkable feature of the galaxies distribution: the galaxy systems are dynamically unstable in the most of the cases.This was confirmed by such observational facts like the abundance of the Trapezium type systems or huge internal motions in some galaxy systems. There are serious reasons to assume that some multiple galaxies and galaxy clusters psently break up because a part of the galaxies forming these systems have spatial velocity sufficient to overcome the gravitation forces and as a result leave their galaxy systems.

These observational facts brought Ambartsumian to an important conclusion that in the psent world of the galaxies there are phenomena of large scale dynamic instability closely related to the new galaxy formation. It means that in the galaxies world the new system origination and evolution processes are on going. Solid evidences were received by the studies of the physical instability manifestations confirming this conclusion.

The discovery by the American astronomers Walter Baade and Rudolf Minkovski of the radio galaxies (galaxies with unusually powerful radio emission equal by the order to their optical radiation) led to research of the various displays of the galaxies physical instability.

Ambartsumian analyzed the existing data on the radio galaxies and deduced that this phenomenon is not caused externally (collisions of the galaxies) as it was supposed by the authors of the discovery, but is a result of the physical instability of the corresponding galaxies.

The study of the observational data of the different types of the physical instability led Amabartsumian to a fundamental conclusion that the processes of the galaxies origination and evolution are mostly dependent of the central condensations — the nuclei. He proved that the all observed cases of galaxy instability are the consequence of the galactic nuclei activity. Later he established that the various degrees of the galaxies nuclei activity produce different structure manifestations (by shape and power) of the galaxies radiation.

Of a great scientific interest are the manifestations of the galactic nuclei activity, connected with the emission of enormous quantities of energy. To such forms of the nuclear activity are attributed the radioflares, the explosions accompanied with ejections of big gaseous masses, the powerful jets of matter and the complete galaxies-satellites, the so called compact galaxies. Among the forms of manifestation of the most powerful energy emission of nuclei are the strong radio-emitting gas clouds observed around the galaxies and the unusually intensive ultraviolet radiation of the galaxies.

The idea of the galactic nuclei activity and the instability of the galaxies physical systems developed by Amabartsumian allowed to understand the inexplicable phenomena and to pdict absolutely new phenomena. His explanation of radio galaxies as a certain stage of galaxies evolution is of a particular scientific importance.

A valuable discovery of the blue ejections and the satellites of the elliptical (blue giant) galaxies was made in Byurakan Observatory. It is difficult to explain the unusual blue color of these formations even if it is assumed that they consist entirely of hot (blue) stars. Therefore, the observed blue formations, being emissions from galaxies nuclei shall be considered as an evidence of unknown states of matter in the galactic nuclei.

Ambartsumian’ s theoretical analysis of the observational data of the known activity manifestations of the galaxies nuclei proves that the nuclei activity is not caused by the stars or by their diffuse matter. The later can not explain the observed forms of the nuclear activity connected to the allocation of enormous quantities of energy and ejections of unusually huge masses of the matter.

Therefore it is necessary to concept that in the corresponding nuclei there are bodies of still unknown nature, containing huge stocks of matter and possessing enormous energy. The physical conditions of matter in the galactic nuclei are extremely unusual and strongly different compared to the conditions observed in the other part of the Universe. In particular in some bodies of the galactic nuclei the matter density should be extremely high. Only in this case, the nuclei can provide a continuous outflow of the matter or emissions and ejections of big masses from the nuclei. It was understood that the galactic nuclei are sources of huge quantities of matter and energy and can form satellite galaxies or galaxy systems and supply them with energy of the observed non-stationary motions. Ambartsumian’ s study on the non-stationary systems of galaxies and the various forms of manifestation of the nuclei activity of separate galaxies has an extraordinary scientific value. It suggests not only the rules of the star and stellar systems origin but also the methods of discovery and research of unknown states of matter, including the proto-stellar matters. Ambartsumian’ s results in this area are in a full consent with the abovementioned theory of the stellar associations: the matter development in the Galaxy has a definite orientationfrom denser states to the less dense ones.

The observations of the last decades made by the world’ s largest telescopes fully confirm Ambartsumians conclusions on the unusual features of the galactic nuclei and their decisive role in the origin and the evolution of the galaxies and their systems. It is worth to emphasize the discovery of quasars — a type of galaxies with nuclei of extremely high activity and the detection of the consequences of the powerful explosions and ejections from the nuclei of some active galaxies.

The study and discovery of the galaxies with unusual strong ultraviolet radiation and galaxies with very active nuclei and compact groups of compact galaxies held under Ambartsumian’ s supervision are very important for the problem of the galaxies origin and evolution.

From L.V. Mirzoyan’ s book «Victor Ambartsumian» («Виктор Амбарцумян»,Ереван, 1985).

The following four papers on this topic that enter in «A Life in Astrophysics» (Allerton Press, 1998), were originally published in:

«Instability phenomena in systems of galaxies,» Astron. Journal, vol. 66, no. 10, pp. 536-540, 1961.

«On the nuclei of galaxies and their activity,» Proceedings of the Thir teenth Conference on Physics at the University of Brussels, September 1964: The Structure and Evolution of Galaxies, Interscience Publish ers, pp.1-14, 1965.

«Problems of extragalactic research,» Invited Discourse at the Gen eral Assembly of IAU,Trans.IAU, vol.XI B, Academic Press, pp. 145-160, 1962.

«Galaxies and their nuclei,» Highlights of Astronomy, G. Contopoulos (ed.), IAU, pp. 51-66, 1974.

Introduction, Nuclei of Galaxies, in Pont. Acad. Scient. Scripta Varia, 35, pp. 1-12, 1971.