Two years after the Event Horizon Telescope (EHT) collaboration captured the first-ever image of a black hole's shadow, the team has unveiled a sharper polarized view, exposing intricate details of its magnetic fields.
At the heart of the massive elliptical galaxy M87 lies a supermassive black hole 6.5 billion times more massive than the Sun, located about 55 million light-years from Earth in the constellation Virgo. In 2019, an international team of astronomers delivered the historic first image: a glowing "smoke ring" precisely matching predictions from Albert Einstein's general relativity equations.
Over the past two years, the EHT researchers have meticulously analyzed their data, zeroing in on light polarization to map the magnetic fields threading the scorching gas orbiting the black hole.
Ordinary light waves vibrate in all directions, but polarized light oscillates in a single plane. This property emerges when light passes through filters like polarized sunglasses or interacts with magnetic fields in hot cosmic plasmas. By observing polarized radio waves—the equivalent of donning polarized lenses—astronomers see M87 as a dynamic swirl of twisted magnetic fields.
This breakthrough image traces those fields to a turbulent plasma ring, roughly 30 billion kilometers in diameter (four times Pluto's orbit from the Sun).
This polarized portrait empowers astronomers to probe the black hole's magnetic environment, shedding light on how it launches powerful cosmic jets.
Black holes are cosmic powerhouses: as infalling matter heats up in the swirling accretion disk, most plunges in, but some is violently ejected as relativistic jets. Understanding this energy conversion process remains a key challenge, making these observations invaluable.
"These relativistic jets represent nature's most extreme phenomena, harnessing gravity, superheated gases, and magnetic fields to propel beams across entire galaxies," says Daniel Holz, astrophysicist at the University of Chicago. "It's thrilling that the EHT is illuminating the processes at a black hole's event horizon fueling these jets."
Janna Levin, astrophysicist at Barnard College, Columbia University, describes the findings as "exciting", offering unprecedented insights into black holes' ability to generate "ray guns spanning thousands of light-years."
These observations also refined estimates of the black hole's feeding rate: a modest thousandth of the Sun's mass per year. Yet this sustains jets stretching thousands of light-years, bright enough for detection across cosmic distances.
Details of this work are published in The Astrophysical Journal here and here.
