The Formation of Planets Around Stars of Various Masses and the Origin and the Evolution of Circumstellar Dust Clouds

Abstract

The formation of planets is investigated both in a gaseous nebula and after the nebula has been blown away. The capture of planetesimals by a protoplanet is investigated by taking into account the growth of planetesimals. The time of planet formation is determined as a function of distance from the central star. The formation time of Neptune is found to be 3.9 × 109 yr, value shorter than the age of the solar system. The region where planets form within the stellar lifetime is determined, and it is found that only stars of mass less than several solar masses can have planets. The dust clouds around α Lyrae and β Pictoris are far outside the planet-forming regions. A model for the circumstellar dust cloud is proposed which can explain the basic properties of the β Pic disk.