Effect of Dust Rotational Disruption by Radiative Torques on Radiation Pressure Feedback from Massive Protostars

Radiation pressure on dust is thought to play a crucial role in the formation process of massive stars by acting against gravitational collapse onto the central protostar. However, dust properties in dense regions irradiated by the intense radiation of massive protostars are poorly constrained. Previous studies usually assume the standard interstellar dust model to constrain the maximum mass of massive stars formed by accretion, which appears to contradict dust evolution theory. In this paper, using the fact that stellar radiation exerts on dust simultaneous radiation pressure and radiative torques, we study the effects of grain rotational disruption by radiative torques (RATs) on radiation pressure and explore its implications for massive star formation. For this paper, we focus on the protostellar envelope and adopt a spherical geometry. We find that originally large grains of micron sizes presumably formed in very dense regions can be rapidly disrupted into small grains by RATs due to infrared radiation from the hot dust shell near the sublimation front induced by direct stellar radiation. Owing to the modification of the size distribution by rotational disruption, the radiation pressure opacity can be decreased by a factor of ~3 from the value expected from the original dust model. However, to form massive stars via spherical accretion, the dust-to-gas mass ratio needs to be reduced by a factor of ~5 as previously found.