Publication: Extracción orbital "in situ" de simulaciones vivas de alta precisión de sistemas no colisionales formados por colapso frío
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2018-05-17
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Universidad Complutense de Madrid
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Abstract
El intervalo de configuraciones autoconsistentes de sistemas autogravitantes, no colisionales, es determinado por la estructura orbital que sustentan, dado que las órbitas son sus bloques constitutivos básicos en el espacio fase (Teorema de Jeans, ver Binney y Tremaine 2008, Sección 4.2). No son las posiciones y velocidades individuales de las partículas las que cuentan, pues aquellas cambiarán de un instante a otro, sino más bien las órbitas a lo largo de las cuales tales partículas se mueven. La distribución global de masa, a través de su campo de fuerza, determina las órbitas que son posibles. A su vez, las fracciones de ocupación de familias orbitales determinan el intervalo de posibles modelos autoconsistentes que pueden existir con esta distribución de masa, algo que es directamente explotado por algunos métodos para construir modelos autoconsistentes, como el método de Schwarzschild (1979). Como tal, determinar la estructura orbital de modelos autoconsistentes es de fundamental importancia. Tradicionalmente, la estructura orbital de modelos no ha sido estudiada extensamente, sino tan sólo sus propiedades dinámicas globales (p.ej., energía y momento angular totales) y locales (p.ej., los momentos de la distribución de velocidades locales, Vorobyov y Theis 2008). Sin embargo, una nueva generación de métodos para construir modelos autoconsistentes hace uso directamente de la composición orbital, p.ej. el método “Hecho a la Medida” de Syer y Tremaine (1996). En particular, las simulaciones de N-cuerpos permiten la construcción de modelos autoconsistentes, pero la colisionalidad debida a su granularidad ha hecho imposible una extracción orbital exitosa de ellos. En un sistema colisional las partículas no siguen órbitas, sino trayectorias, que son concatenaciones de segmentos de órbitas, dado que las colisiones dispersan a las partículas en el espacio orbital. Fue sólo cuando las simulaciones de N-cuerpos pudieron seguir del orden de 106 partículas, que la granularidad fue reducida al punto donde las primeras órbitas pudieron extraerse directamente de una simulación de N-cuerpos (Ceverino y Klypin 2007)...
The range of self-consistent configurations of collisionless, self-gravitating systems, is determined by the orbital structure they support, as orbits are their basic building blocks in phase space (e.g. Jeans’ Theorem, see Binney & Tremaine 2008, section 4.2). It is not the individual positions and velocities of the particles that matter, as these will change from one instant to another, but rather the orbits along which they move. The overall mass distribution, through its force field, determines the orbits that are possible. In turn, the occupation fractions for each orbit determine the range of possible self-consistent models that can exist with this mass distribution, something directly exploited by some methods to build self-consistent models, like Schwarzschild’s (1979) method. As such, determining the orbital structure of self-consistent models is of paramount importance. Traditionally, the orbital structure of models has not been extensively studied, but rather the global (e.g. overall energy and angular momentum), and local (e.g. moments of the local velocity distribution) dynamical properties (e.g. Vorobyov & Theis 2008). However, a new generation of methods to build self-consistent models uses directly the orbital makeup, e.g. the “Made to Measure” method of Syer and Tremaine (1996). In particular, N-body simulations allow the construction of self-consistent models, but the collisionality due to their graininess had made impossible the successful extraction of orbits from them. In a collisional system, particles do not follow orbits, but trajectories that are piecewise orbits, as collisions scatter particles in orbital space. It was only when N-body simulations were able to follow of the order of 106 particles, that the graininess was able to be pushed down where the first orbits could be extracted directly from an N-body simulation (Ceverino & Klypin 2007)...
The range of self-consistent configurations of collisionless, self-gravitating systems, is determined by the orbital structure they support, as orbits are their basic building blocks in phase space (e.g. Jeans’ Theorem, see Binney & Tremaine 2008, section 4.2). It is not the individual positions and velocities of the particles that matter, as these will change from one instant to another, but rather the orbits along which they move. The overall mass distribution, through its force field, determines the orbits that are possible. In turn, the occupation fractions for each orbit determine the range of possible self-consistent models that can exist with this mass distribution, something directly exploited by some methods to build self-consistent models, like Schwarzschild’s (1979) method. As such, determining the orbital structure of self-consistent models is of paramount importance. Traditionally, the orbital structure of models has not been extensively studied, but rather the global (e.g. overall energy and angular momentum), and local (e.g. moments of the local velocity distribution) dynamical properties (e.g. Vorobyov & Theis 2008). However, a new generation of methods to build self-consistent models uses directly the orbital makeup, e.g. the “Made to Measure” method of Syer and Tremaine (1996). In particular, N-body simulations allow the construction of self-consistent models, but the collisionality due to their graininess had made impossible the successful extraction of orbits from them. In a collisional system, particles do not follow orbits, but trajectories that are piecewise orbits, as collisions scatter particles in orbital space. It was only when N-body simulations were able to follow of the order of 106 particles, that the graininess was able to be pushed down where the first orbits could be extracted directly from an N-body simulation (Ceverino & Klypin 2007)...
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Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Astrofísica y Ciencias de la Atmósfera, leída el 14-07-2017