Circular Polarization of the CMB: A probe of the First stars

Understand

While it is revealed that the Cosmic Microwave Background (CMB) is linearly polarized at 10 % level, it is predicted that there exists no significant intrinsic source for circular polarization (CP) in the standard cosmology.

• However, during the propagation through a magnetised plasma, the CP of the CMB could be produced via the Faraday conversion (FC).
• The FC converts a pre-existing linear polarization into CP in presence of a magnetic field with relativistic electrons.
• In this paper, we focus on the FC due to supernova remnants of the first stars, also called Pop III stars.