Polarization hole in a starless core

The near infrared polarization is produced by a mixed population of grains from the core border and the cloud gas. The optical and near infrared polarization toward the cloud reach the maximum possible value and saturate with respect to the visual extinction. The core polarization is predominantly traced by the submillimeter data and have a steep decrease with respect to the visual extinction.

Modeling of the submillimeter polarization indicates a magnetic field main direction projected onto the plane-of-sky and loss of grain alignment for densities higher than 6x10^4^cm^-3^ (or A_V_>30mag). Pipe-109 is immersed in a magnetized medium, with a very ordered magnetic field. The absence of internal source of radiation significantly affects the polarization efficiencies in the core, creating a polarization hole at the center of the starless core.

This result supports the theory of dust grain alignment via radiative torques.