Author: Publisher:
ISBN:
Category : Galaxies
Languages : en
Pages : 376
Book Description
Instabilite Gravitationnelle Et Formation Des Etoiles, Des Galaxies Et de Leurs Structures Caracteristiques
Author: NASA Technical Report
Author: Dynamical Evolution of Disk Galaxies
Author: Frank HohlPublisher:
ISBN:
Category : Galaxies
Languages : en
Pages : 116
Book Description
A computer model for isolated disks of stars is presented and is used to study the self-consistent motion of large numbers of point masses as they move in the plane of the galactic disk. The Control Data 6600 computer system at the Langley Research Center was used to integrate the equations of motion for each star for systems containing from 50,000 to 200,000 stars. Any initially cold balanced disk was found to be violently unstable. A sufficient amount of velocity dispersion will stabilize all small-scale disturbances. However, most disks investigated were found to be unstable against slowly growing long-wavelength modes, and after about two rotations the disks tended to assume a bar-shaped structure. It was also found that the final mass distribution for most disks could be closely approximated by an exponential variation irrespective of the initial mass distribution. To study the development of spiral structure, the model was modified to include a fixed central force similar to that in the Schmidt model of the Galaxy. The mass of the stars in the disk was taken to be from 5 to 50 percent of the total mass of the Galaxy. The evolution of a number of initial distributions of stars was investigated. The results of the calculation gave a velocity dispersion for the disk stars which was about 50 percent larger than the value of about 30 km/sec found from observation of stars in the solar neighborhood. For some of the disks investigated, a pronounced spiral structure remained even after 8.5 rotations.
Theory and Results on Collective and Collisional Effects for a One-dimensional Self-gravitating System
Author: Frank HohlPublisher:
ISBN:
Category : Astrophysics
Languages : en
Pages : 92
Book Description
The equilibrium properties of one-dimensional self-gravitating systems are investigated analytically. One-dimensional models are used to perform computer experiments tracing the evolution of stellar systems. The stationary solution of the Vlasov equation for a one-dimensional system of stars as computed for an interesting class of initial conditions is found to correspond to a minimum-energy configuration. The results of the numerical experiments are compared with theory. For initial energies far from the minimum equilibrium energy the system becomes unstable and breaks up into smaller clusters. A variational principle was applied to the one-dimensional stellar system to show that stationary distribution functions which decrease monotonically in going outward from the center of the system are stable. That other stationary distributions may be unstable is illustrated by means of computer experiments. The one-dimensional model is of interest as an approximation to the distribution of velocity and mass normal to the galactic plane of a greatly flattened galactic system. Observational results for the gravitational force normal to the galactic plane of the Galaxy agree with the results obtained from the one-dimensional model. Thermalization effects for systems containing small numbers of stars were investigated. The fluctuation of the kinetic energy was found to be inversely proportional to the square root of the number of particles in the system.
Scientific and Technical Aerospace Reports
Author: Nuclear Science Abstracts
Author: International Aerospace Abstracts
Author: Collection in 8.̊
Author: Université de Liège. Institut d'astrophysiquePublisher:
ISBN:
Category : Astrophysics
Languages : en
Pages : 386
Book Description
Chiefly reprints.
Nuclear and Relativistic Astrophysics and Nuclidic Cosmochemistry: 1963-1967
Author: Bronisław KuchowiczPublisher:
ISBN:
Category : Astrophysics
Languages : en
Pages : 270
Book Description
Author: