Protoplanetary discs and axion dark matter

A May 2019 paper in Physical Review Letters (full refereed paper- needs a login; see here for the preprint) suggests that polarised light from protoplanetary discs may be used to search for axion-mass dark matter, around the 10^-22 eV scale.

The basic idea is that, via axion-photon coupling, axion dark matter in that mass regime should cause rotation of the plane of linearly-polarised light from starlight that is scattered by the host star’s protoplanetary disc (PPD). The reason for observing a PPD in particular is that they provide a known physical structure (i.e. an essentially flat disc), and, for an appropriate object, one in which the plane of the disc is nearly at right-angles to our line of sight.

This allows us to model the linear polarisation that we expect to see from the disc, in the absence of intervening axion DM particles. We can also model what we would expect to see in the presence of intervening axion DM (again, in the mass range in question).

Spatially-resolved polarimetry of a protoplanetary disc should allow us to test for this. Initial observations of the PPD surrounding the star AB Aurigae suggest that the observed polarimetry pattern is consistent with the expected source pattern, which can be used to provide limited on the axion-photon coupling at the very small axion masses which this technique probes.