Ambartsumian’ s view on astronomy of XX century

Ambartsumian on stellar systems

Here are papers on this topic, that enter in «A Life in Astrophysics. Selected papers of V.A. Ambartsumian»,Edited by Rouben Ambartsumian, Allerton Press, 1988:  

«On the derivation of the frequency function of space velocities of the stars from the observed radial velocities.»

«The statistics of double stars.»

«On the dynamics of open clasters.»

«Multiple systems of Trapezium type».


The dynamics and the statistical mechanics of the stellar systems


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

Ambartsumian’ s research of the stellar systems dynamics is of a fundamental value. His ideas reveal the nature of the star formation process in the Galaxy.

Here is the main essence of Amabrtsumian’ s new ideas on the stellar dynamics.

In a stellar system each star in a motion is influenced by two kinds of forces: 1) joint attraction forces of the all other stars of the system (regular forces). 2) perturbation forces arising as a result of the close passages of stars (irregular forces). The time interval when the influence of the irregular forces in the given stellar system is equal to the influence of the regular forces, is called the system relaxation time. Ambartsumian estimates the relaxation time for our stellar system Galaxy as about 1019years. It means that the influence of the irregular forces in the Galaxy is insignificantly small due to the rare close passages of the stars. Therefore in many problems of the star dynamics the Galaxy could be considered as a system where the stars move under the influence of only regular forces.

In the real stellar systems the influence of the irregular forces not always should be neglected. In some of them (multiple stars, stellar clusters) the irregular forces can play a vital role. On the other hand the stars in the stellar systems interact according to the Newton’ s universal gravitation law. As a result many common methods of the statistical physics are inapplicable to real stellar systems.

Ambartsumian developed the fundaments of the new physical statistics taking into consideration these features of the real stellar systems — the statistical mechanics of the stellar systems.

The scientist came to results of supme value by application of the original methods of the statistical mechanics to the stellar systems to double stars and stars clusters, in particular to the age estimations of the stellar systems and the determination of the age of the Galaxy.

In their motions inside a star cluster the stars belonging to the system often change their positions, bringing to a redistribution of the stars velocities. Some cluster stars get velocities sufficient to overcome the gravitation field of the system and part from the cluster. The dwarf stars with small masses are thrown out from the cluster the first. The calculations show that the time necessary for semi-decay of the star clusters does not exceed ten billion years. The observation data on the total number of the cluster stars and the dwarf stars shows that many clusters of the Galaxy have not broken to half yet. Based on this observation Ambartsumian concluded that the duration of the modern state of the Galaxy (its age) does not exceed ten billion years.

This result was confirmed by the statistical researches of double stars.

A single star at a close passage of a double star gets changes of its orbit elements. The accidental character of the close passages demonstrates that the equilibrium of the distribution of the orbit elements in the Galaxy is not yet established. This can be considered as a proof of the mentioned estimation of the age of the Galaxy.

Formation and disintegration processes occur as the result of the close passages of the stars by the double stars. In time a state of equilibrium establishes between these two processes when after a certain time the number of the breaking up pairs of the double star is equal at average to the number of the formed pairs. In case of the wide pairs about ten billion years are necessary for an establishment of dissociative equilibrium in the Galaxy.

Ambartsumian showed that the fraction of the wide pairs in the respect of the single stars expected at the dissociative equilibrium is a few tens of millions times less than observed fraction in the Galaxy. This observational fact means that there is no dissociative equilibrium in the Galaxy yet.

Ambartsumian disproved the dominating concept of the English Scientist James Jeans who defined the age of the Galaxy as ten thousand billion years old by the «long time scale». Ambartsumian proved that the «long time scale» was a result of a wrong interptation of the observational data of the orbit elements of the double stars.In fact this data indicates the «short time scale» around ten billion years, what is in thousand times shorter than the «long scale». The estimation of the Galaxy age given by Ambartsumian, received a general recognition.

Ambartsumians general theory of derivation of the space velocities distribution from the observed radial velocities is of a big scientific value.

Ambartsumians result obtained from his study of RR Lyrae type variable stars, showing a short-term periodic variations of brightness has a fundamental significance for the problem of the origin and evolution of the stars. He demonstrated that the time intervals, required for a significant change in spatial distribution or in the distribution of the spatial velocities of the stars of certain type, many times exceed the duration of the life of this stars. This result leads to a conclusion that the observable distributions of the specified values during the life of the stars of the given type practically do not change. Therefore the stars repsenting various stages of evolution of a given type should have similar distributions both in the space and in the velocities (should have identical spatial-kinematic characteristics).

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

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

On the derivation of the frequency function of space velocities of the stars from the observed radial velocities,» Mon.

Not.R. Astr.Soc, vol. 96, no. 3, pp. 172-179, 1936.

«К статистике двойных звёзд,» Астр. журн.[Sov. Astr.], vol. 14, no. 3, pp. 207-219, 1937.

«К вопросуо динамике открытых скоплений,»Уч.записки ЛГУ [Uch. Zap. LGU], no. 22, pp. 19-22, 1938.