Galaxies and Their Nuclei

Abstract

Our Extraordinary General Assembly is devoted to the memory of one of the greatest men of science to the genial Polish astronomer -Nicolaus Copernicus. The main service of Copernicus which has made his name immortal was in finding the correct interpretation of the planetary motions we observe. Instead of geocentric notions, which proved unable to explain the accumulated bulk of empirical data on the apparent motions of planets he has put forward and advocated the notion of a solar system thus presenting the true picture of the part of the Universe we live in. The scientific revolution started by him was continued by Galileo and Kepler and was crowned with the great theoretical generalizations of Newton. As a result a foundation has been created for the most exact theories of motions in the solar system which were developed during the next centuries. These theories in their modern form give also the possibility to solve all the problems concerning the orbital motions of spaceships.At this stage we can not yet boast that in the study of nuclei of galaxies and their activity we have reached the level which existed in planetary astronomy even before the works of Newton. Only 15 years elapsed from the moment when the idea of activity of nuclei of galaxies was cleaily formulated (Ambartsumian, 1958). During these years discoveries of the greatest importance have been made. New unexpected discoveries occur almost each year. These discoveries influence decisively our notions on the diversity of objects and phenomena in the distant space, but they are still insufficient foi the construction of adequate theories. In order to penetrate into the very nature of nuclear phenomena we require new observations, new measurements and new data. And if some optimists imagine that the time has already ripen to build a general theory of these phenomena, the more cautious astronomers would like to considei a more or less satisfactory systematization of observational data concerning the activity of nuclei and the understanding of external physical processes accompanying it as a tremendous success.These external processes reach often such a large scale that they influence the appearance and integral parameters characterizing the galaxies. Therefore the study of the nature and the activity of nuclei sometimes means to investigate the problems of the structure of galaxies and of their evolutionary changes.In this report we consider some properties of galaxies which are immediately connected with the activity of nuclei and ultimately with the nature of nuclei themselves.

Kinematics of OB-associations in Gaia epoch

“…Gaia DR1 contains the Tycho-Gaia Astrometric Solution (TGAS, Michalik, Lindegren & Hobbs 2015;Lindegren et al 2016) which provides positions, parallaxes and proper motions for about 2 million stars using the 24 yr time difference between Hipparcos (ESA 1997;Hog et al 2000) and Gaia (Gaia Collaboration et al 2016a) observations. The term 'OB-association' was first introduced by Ambartsumian (1949). The sizes of OB-associations differ from 10 pc (Cyg OB2) to 500 pc (Cep OB1), although the sky-plane sizes of 90 percent of them do not exceed 200 pc (Blaha & Humphreys 1989).…”

Kinematics of the Scorpius-Centaurus OB association

“…The hypothesis of a low space density and, as a result, dynamical instability of associations in the field of Galactic tidal forces was also first put forward by Ambartsumian (1949).…”

New Expansion Rate Estimate of the Scorpius–Centaurus Association Based on T Tauri Stars from the Gaia DR2 Catalog

“…However, in this case, the neighborhood under consideration is small, and the position angle θ → 0 • in formula (6). Under this condition, it can be easily shown that the inclusion of a spiral wave does not depend on m. Indeed, in accordance with relation (7), we have cot(i) = 2πR 0 /λm.. After substituting into (6), m is canceled. Thus, considering the influence of a spiral density wave, it is necessary to have four parameters: λ, f R , f θ and χ ⊙ .…”