輻射力矩對塵埃的破壞及對日光層塵埃尺寸演變的影響的研究

Abstract

本論文探討了輻射扭矩破壞（Radiative Torque Disruption, RATD）機制在太陽系內將微米級塵埃顆粒破碎成奈米顆粒過程中的作用。通過分析在不同離心力應力下的破壞時間尺度，我們證明RATD是一種高效分解微米級顆粒的過程，其效果超越其他破碎機制。此外，RATD抑制了輻射壓力對微米級顆粒的驅逐，改變了它們在太陽系內的動力學行為。

研究揭示RATD顯著改變水雪線（water snow line）位置，使其超越熱力學定義的邊界，突顯溫度與顆粒尺寸對日球層動力學的雙重影響。對於較小的顆粒，由於RATD的影響，雪線可以延伸到其熱力學定義位置之外。此外，我們建立了一個簡化模型來描述由RATD修改後的顆粒大小分佈，揭示了微米級顆粒數密度的顯著減少以及次微米級顆粒數量的相應增加。然而研究顯示，若少於80\\%塵埃顆粒通過輻射扭矩作用於高$J$吸引子（high-$J$ attractors）達到定向排列，RATD對顆粒尺寸分布的影響將顯著減弱。

最後，我們提出了測試RATD機制的實驗方法，並討論了將我們的模型應用於太陽系塵埃研究時的不確定性。

This thesis investigates the role of the Radiative Torque Disruption (RATD) mechanism in the fragmentation of micrometer-sized dust grains into nanoparticles within the heliosphere. By analyzing the disruption timescales under varying centrifugal stresses, we demonstrate that RATD is an efficient process for breaking down micrometer-sized grains, surpassing other fragmentation mechanisms in its effectiveness. Additionally, RATD inhibits the expulsion of micrometer-sized grains by radiation pressure, altering their dynamical behavior within the heliosphere.

This study reveals that RATD significantly alters the water snow line's position beyond its thermally defined boundary, emphasizing the dual influence of temperature and grain size on heliospheric dynamics. For smaller grains, the snow line can extend beyond its thermally defined position due to the impact of RATD. Furthermore, we construct a simplified model to characterize the grain size distribution modified by RATD, revealing a substantial reduction in the number density of micrometer-sized grains and a corresponding increase in sub-micrometer-sized grains. However, we find that if fewer than 80\\% of dust grains are aligned at high-$J$ attractors by radiative torques, the impact of RATD on the grain size distribution is significantly weakened.

Finally, we propose experimental approaches to test the RATD mechanism and discuss the uncertainties associated with applying our model to heliospheric dust studies.