| Contents |
1. Lindblad's Era >>
Density-Wave Spiral Theories in the 1960s. I
I.I. Pasha
| You men are strange people - said Amaranta, unable to think up anything else. - All your life you fight against priests, but give prayer-books. |
| G.G. Marquez. A hundred years of solitude |
| ...&nbap;a common foible of those who in the feeling of devotion are disposed to exaggerate the significance of their heroes. |
| Einstein 1953 |
INTRODUCTION 2
The modern density-wave theory of spiral structure in galaxies, sprung in the 1960s, had long been preceded by the theories of Bertil Lindblad. Those started back in the days when Hubble demonstrated that whirlpool nebulae reside far outside the Galaxy, and when Jeans conveyed an engrossing feeling of steady spirals ordered by yet unknown forces. 3 Astronomer by education, Lindblad did not yield to temptation by this imposing obscurity of force, and he headed for a dynamical spiral theory in terms of ordinary gravitation. 4 Right then, this task must have appeared extremely difficult, to be at best a matter of a lifetime of work, since the analytical methods of the patronizing disciplines (hydrodynamics, statistical mechanics) were rudimentary and gave almost nothing for the stellar-dynamical research. Still more striking was Lindblad's break-through in the field of stellar kinematics. By 1927 already he developed the theory of epicycles, having shown that a star moving on a nearly circular galactic orbit just oscillates about its mean radius (Lindblad 1926b). The frequency of such oscillations was given by the relations
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(1) |
including the angular speed , the Oort constant of differential rotation A - 1/2 rd / dr, and the azimuthal-to-radial velocity dispersion ratio (Lindblad 1927b); the values of c / cr got remarkably close as calculated and empirically determined for the solar neighborhood (Lindblad 1929). These results reinforced the stellar-dynamical foundations and also they gave Lindblad confidence in his search of the origins and mechanisms of the galactic spiral phenomenon, but, quickly recognized and instigated by success, he was taken hostage, then and on, to the epicyclic-orbit scheme.
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Публикации с ключевыми словами:
история астрономии - спиральная галактика - волны плотности - спиральная структура
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