Monday, April 05, 2021 at 12:40

https://cuboulder.zoom.us/j/96981439846

Andrew Chael, Princeton

"Magnetic Fields at a Supermassive Black Hole's Event Horizon"

Abstract:

The Event Horizon Telescope (EHT) is a global network of radio antennas; combining the signals from sites separated by thousands of kilometers using Very Long Baseline Interferometry (VLBI), the EHT synthesizes images with the resolution of an Earth-sized telescope. In 2017, The EHT observed the supermassive black hole at the core of the M87 galaxy. The EHT images revealed a compact asymmetric ring with a size only a few times that of the black hole's event horizon. This ring is produced by synchrotron emission as relativistic electrons in the hot plasma around the black hole spiral around magnetic field lines. New images from the EHT have now revealed the polarized part of this emission, which directly probes the structure of the magnetic fields and the properties of the plasma near the black hole. In this talk I will discuss the challenges involved in producing a polarized image from the sparse EHT data, as well as the new insights these images provide into the structure of the region just outside the event horizon. The EHT images show a polarization pattern that is predominantly azimuthal; we find these images are consistent with simulations of magnetically arrested accretion disks, where the near-horizon magnetic fields are strong and push back on the infalling plasma. These strong fields are responsible for launching the powerful relativistic jet from the black hole that extends to outside the M87 galaxy.

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