Study of Stellar Dynamics: Theory and Simulations

Sanjayan, Sachu (2016) Study of Stellar Dynamics: Theory and Simulations. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Sachu Sanjayan (11MS054)) Sachu-11054.pdf - Submitted Version Restricted to Repository staff only Download (2MB)

Abstract

The Stellar dynamics involves the motion of stars or star systems like galaxies or star clusters. It’s interaction with stars or system of stars which governs the trajectory of it’s motion. At first the overall dynamics of the stars in galactic systems were studied. The Rotation Curves are found at different radii of the galaxy. There arises the Galactic Rotation Problem also known as the missing mass problem. Theory and observations were not matching at disk and halo part of the rotation curve. Many proposals came up with brilliant ideas. Some Argued its because of the modification in the Newtonian Gravity and MACHOs, WIMPs, Neutrinos even the idea of Parallel Universe came. Other reasonable proposal was the evidence of dark matter spread along the galaxy instead of concentrating at the center. Hence,different dark matter models of the system were studied. The indirect evidences of the dark matter is found. Using different models such as density and potential model the observed data is fitted and simulations are tested. Plummer, Logarithmic and Miyamoto Nagai potential models showed best fits for different types of galaxies. Now we moved to chase the individual stars to study their orbits. This is the prequel to study advanced and complex systems like globular clusters. Using equations of motion the trajectories and phase space diagrams are studied for different dark matter potential models. We choose plummer model for simulation of clusters. Globular clusters are strong gravitationally bound system of stars. They are much older than Galaxy or other open clusters. Thats the reason why globular clusters are studied for the understanding of Dynamics of stellar systems and star formations. Now getting started with the globular cluster simulations. There are different velocity dispersion models like King and Michie. They are tested using the density and potential to make sure the models are consistent with globular clusters. Now using Montecarlo simulations the initial position, velocity and mass of the stars are set. Individual potential, Energy and Angular momentum are calculated. The system is allowed to evolve in time. For that we have used the equations of motion and calculated the trajectories of each star. Using Globular Capture ,Escape velocity and Tidal encounters disturbances are applied to the system. The collision and near encounters are simulated using a random distribution of Virial velocity of the system. For different cases and parameters the system is tested. The system is allowed to evolve till it completely collapse and evaporate.

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