Aligned grains and scattered light found in gaps of planet-forming disk.

Polarized (sub)millimetre emission from dust grains in circumstellar disks was initially thought to be because of grains aligned with the magnetic field. However, higher-resolution multi-wavelength observations and improved models found that this polarization is dominated by self-scattering at shorter wavelengths (for example, 870 µm) and by grains aligned with something other than magnetic fields at longer wavelengths (for example, 3 mm). Nevertheless, the polarization signal is expected to depend on the underlying substructure, and observations until now have been unable to resolve polarization in multiple rings and gaps.

Hunting Axion Dark Matter with Protoplanetary Disk Polarimetry.

We find that the polarimetric observations of protoplanetary disks are useful to search for ultralight axion dark matter. Axion dark matter predicts the rotation of the linear polarization plane of propagating light, and protoplanetary disks are ideal targets to observe it. We show that a recent observation puts the tightest constraint on the axion-photon coupling constant for an axion mass m≲10^{-21}  eV.