Grain Alignment and Disruption by Radiative Torques in Dense Molecular Clouds and Implication for Polarization Holes

Dust polarization induced by aligned grains is widely used to study magnetic fields in various environments, including star-forming regions. However, the question of what optical depth grain alignment still exists a dense molecular cloud (MC) unclear. In this paper, we aim achieve analytical formulae for minimum size ($a_{\rm align}$) and rotational disruption disr}$) RAdiative Torques (RATs) as function local physical parameters within MCs. We first find approximations radiation strength mean wavelength attenuated field MC without with embedded stars then derive $a_{\rm align}$ disr}$ functions visual extinction $A_{V}$ gas density. that starless core density $n_{\rm H}\sim 10^{5}\rm cm^{-3}$, $a<0.25\mu m$ can be up $A_{V}\sim 5$ RATs, whereas micron-sized at 50$. The increase explain presence holes observed toward cores. For MCs an protostar, efficiency both increases protostar due increasing strength. Such effect results decrease degree or emission intensity, which reproduces popular location protostars. Finally, formula maximum where discuss its potential constraining growth.