Two years ago, the Event Horizon Telescope (EHT) made headlines with its announcement of the first direct image of a black hole. Science magazine named the image its Breakthrough of the Year. Now the EHT collaboration is back with another groundbreaking result: a new image of the same black hole, this time showing how it looks in polarized light. The ability to measure that polarization for the first time—a signature of magnetic fields at the black hole's edge—is expected to yield fresh insight into how black holes gobble up matter and emit powerful jets from their cores. The new findings were described in three papers published in The Astrophysical Journal Letters.
"This work is a major milestone: the polarization of light carries information that allows us to better understand the physics behind the image we saw in April 2019, which was not possible before," said co-author Iván Martí-Vidal, coordinator of the EHT Polarimetry Working Group and a researcher at the University of Valencia, Spain. "Unveiling this new polarized-light image required years of work due to the complex techniques involved in obtaining and analyzing the data."
As Ars' John Timmer reported back in 2019:
