Theoretical model of nucleation for cosmic dust formations

2018 Fiscal Year Final Research Report

• Project/Area Number: 15K05015
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Astronomy
• Research Institution: Tohoku University (2018); Hokkaido University (2015-2017)
• Principal Investigator: Kyoko Tanaka 東北大学, 理学研究科, 客員研究者 (70377993)
• Project Period (FY): 2015-04-01 – 2019-03-31
• Keywords: 宇宙ダスト / 凝縮 / 核生成

Outline of Final Research Achievements

The condensation and crystallization processes are important for understanding the origin of cosmic dusts and have seen by various observations.　We performed direct large molecular dynamics simulations of homogeneous nucleation of water which is an important component of cosmic dusts. We obtained nucleation rates and found a scaling relation of nucleation rate with remarkable consistency. We also performed molecular dynamics simulations of vapor-to-solid phase transition and discuss the transition process. Our simulations indicate that the vapor-to-solid transition occurs through multistep nucleation which is vapor-to-liquid nucleation (first step nucleation) and crystallization in the supercooled liquid droplets (second step nucleation), even though the temperature is much lower than the triple temperature. Our results indicate that the multistep nucleation is a common phenomenon in the first stage of condensation from vapor to solid in the astrophysical environments.

Free Research Field

天文学、物質科学

Academic Significance and Societal Importance of the Research Achievements

本研究の特徴は、宇宙ダスト生成を考える際の最も根本となる基礎理論を、分子レベルで解明し、宇宙環境におけるさまざまな温度圧力場でも使える核生成モデルを導き出すことにある。核生成率の不定性は宇宙のみならず他分野に関わる未解決な大問題であるが、分子動力学計算は分子レベルでの全く新しい情報を得ることが可能であり、核生成過程を詳細に調べる強力なツールである。また粒子数を多くした大規模計算により、小さい核生成率かつ大きな凝縮核のデータを得ることが可能になった。この手法をさまざまな物質に広げることにより、宇宙環境に使える理論モデルを構築できる。