Circumstellar discs are the reservoirs of gas and dust that surround young stars and have the potential to become planetary systems. Their evolution will determine the time and material available... Show moreCircumstellar discs are the reservoirs of gas and dust that surround young stars and have the potential to become planetary systems. Their evolution will determine the time and material available to form planets. Studying the evolution of circumstellar discs can then help us understand planet formation and the diversity of observed planetary systems. These discs develop almost immediately after star formation, as a direct consequence of the collapse of a molecular cloud and angular momentum conservation. Their surroundings are rich in gas and neighbouring stars, which can be hostile to the discs and affect their evolution in different ways: dynamical encounters with nearby stars can truncate the discs; stellar winds and supernovae explosions can truncate, tilt, or completely destroy the discs; and the presence of bright, massive stars in the vicinity of circumstellar discs can heat their surface enough to evaporate mass from them. This process, known as external photoevaporation, is arguably one of the most important environmental mechanisms in depleting mass from young circumstellar discs. The work performed for this thesis consisted of simulating the early evolution of circumstellar discs in star clusters and the effects of the environment, in particular, truncations due to close encounters and photoevaporation. The results show that photoevaporation is extremely efficient in removing mass from the discs, greatly limiting the amount of material and time available to form planets. Show less
Ever since Isaac Newton in 1687 posed the N-body problem, astronomers have been looking for its solutions in order to understand the evolution of dynamical systems, such as our own solar system,... Show moreEver since Isaac Newton in 1687 posed the N-body problem, astronomers have been looking for its solutions in order to understand the evolution of dynamical systems, such as our own solar system, star clusters and galaxies. The main difficulty is that small errors grow exponentially, so that numerical solutions diverge easily from the mathematical solution. This thesis presents two new state of the art N-body algorithms, one of which is designed for high precision (Brutus) and the other for speed (Sakura). The assumption that N-body results are accurate in a statistical sense, is put to the test for three-body configurations. Finally, a new mathematical model is constructed that describes the origin of chaos in a dynamical systems, and explains the short Liapounov time of Comet Halley's orbit. Show less
Stars near massive black holes move on elliptical orbits which precess slowly, exerting persistent gravitational torques on each other. In this the- sis we present four important consequences of... Show moreStars near massive black holes move on elliptical orbits which precess slowly, exerting persistent gravitational torques on each other. In this the- sis we present four important consequences of these gravitational torques: 1) A new instability which exposes the inherently unstable nature of ec- centric stellar disks in galactic nuclei, 2) A density depression of stars near massive black holes due to enhanced angular momentum relaxation and tidal disruptions, 3) A signature of high-eccentricity orbits for stars formed by Hills__ mechanism at large radii from the massive black hole, and a directly-observable statistic that can highlight these populations, and 4) A new dynamical process which we call "secular dynamical anti-friction" which boosts the orbital eccentricity of hypothesized intermediate-mass black holes as they spiral into massive black holes Show less
