| Contents |
1. Lindblad's Era >>
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
...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
 |
(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.
2 Throughout the paper, the italicized names in parentheses refer to private communications as identified in the note to the list of references. Back.
3 "Each failure to explain the spiral arms makes it more and more difficult to resist a suspicion that the spiral nebulae are the seat of types of forces entirely unknown to us, forces which may possibly express novel and unsuspected metric properties of space. The type of conjecture which presents itself, somewhat insistently, is that the centres of the nebulae are of the nature of `singular points', at which matter is poured into our universe from some other, and entirely extraneous, spatial dimension, so that, to a denizen of our universe, they appear as points at which matter is being continually created" (Jeans 1929, p.360). Back.
4 Polemizing with Jeans on the spiral problem, Brown, a celestial mechanician from Yale University, defended already its gravitational status. In his mind, star orbits might at certain conditions correlate in shape and orientation so as to reveal a two-armed spiral-like envelope, thus delineating a "visible structure [...] due to the greater space density of visible matter in the neighborhood of the arms than elsewhere", i.e. a stationary wave of condensation (Brown 1925, p.109-10). Noticed though (Jeans 1929; Lindblad 1927c), Brown's work had no perceptible impact. Back.
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Publikacii s klyuchevymi slovami:
istoriya astronomii - spiral'naya galaktika - volny plotnosti - spiral'naya struktura
Publikacii so slovami: istoriya astronomii - spiral'naya galaktika - volny plotnosti - spiral'naya struktura | |
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