First M87 Event Horizon Telescope Results. VIII. Magnetic Field Structure near The Event Horizon

Understand

Event Horizon Telescope (EHT) observations at 230 GHz have now imaged polarized emission around the supermassive black hole in M87 on event-horizon scales.

• This polarized synchrotron radiation probes the structure of magnetic fields and the plasma properties near the black hole.
• Here we compare the resolved polarization structure observed by the EHT, along with simultaneous unresolved observations with the Atacama Large Millimeter/submillimeter Array, to expectations from theoretical models.
• The low fractional linear polarization in the resolved image suggests that the polarization is scrambled on scales smaller than the EHT beam, which we attribute to Faraday rotation internal to the emission region.