Three-dimensional magnetic field imaging of protoplanetary disks using Zeeman broadening and linear polarization observations
In one sentence
A theoretical and computational blueprint for measuring the full three-dimensional magnetic field in a protoplanetary disk, by combining the broadening of unpolarized line emission (sensitive to field strength) with the linear polarization of the same line (sensitive to field orientation).
What’s the question?
We do not just want to know how strong the magnetic field is in a planet-forming disk; we want to know where it points. How does it thread the disk? Is it mostly poloidal (vertical) or toroidal (in-plane)? Does its orientation flip across rings and gaps? A single observable cannot tell you all of that. We needed a method that reads field strength and field orientation from independent, simultaneous diagnostics.
What did we do?
We refined the theory of the Zeeman effect in spectral lines and applied it to the (polarized) radiative transfer of CN excited in a protoplanetary disk. The key insight: the Zeeman broadening of the unpolarized line — invisible at first glance, but recoverable from very high-resolution spectra — is the most sensitive diagnostic of disk field strength, while the linear polarization of the same line gives the field orientation. Combined, the two reconstruct the full 3-D field vector.
Why does it matter?
This is the methodological foundation that, two years later, was used to make the first radially resolved magnetic-field measurement in a real disk (Teague, Lankhaar et al. 2025). Beyond TW Hya, the framework defines the path that ALMA — and eventually the SKA — will follow to map disk magnetic fields systematically.
My role
First author. Led the development of the Zeeman-broadening method, performed the radiative-transfer simulations, and wrote the paper.