The team measured how that light is linearly polarized. The Event Horizon Telescope made observations at a wavelength of 1.3 mm. Fortunately, the intense gravity of the black hole warps light and magnifies the event horizon so that it appears larger on the sky - about 50 micro-arcseconds, a region that the EHT can easily resolve. And since it's located 25,000 light-years away, this size corresponds to an incredibly small 10 micro-arcseconds across. The Milky Way's central black hole, Sgr A* (Sagittarius A-star), weighs about 4 million times as much as our Sun, yet its event horizon spans only 8 million miles - smaller than the orbit of Mercury. Such resolution is needed because a black hole is the most compact object in the universe. (An arcsecond is 1/3600 of a degree, and 15 micro-arcseconds is the angular equivalent of seeing a golf ball on the moon.) Since larger telescopes can provide greater detail, the EHT ultimately will resolve features as small as 15 micro-arcseconds. This feat was achieved using the Event Horizon Telescope (EHT) - a global network of radio telescopes that link together to function as one giant telescope the size of Earth. Our data puts decades of theoretical work on solid observational ground," adds principal investigator Shep Doeleman (CfA/MIT), who is assistant director of MIT's Haystack Observatory. "These magnetic fields have been predicted to exist, but no one has seen them before. Nobody has been able to resolve magnetic fields near the event horizon until now," says lead author Michael Johnson of the Harvard-Smithsonian Center for Astrophysics (CfA). "Understanding these magnetic fields is critical. For the first time, astronomers have detected magnetic fields just outside the event horizon of the black hole at the center of our Milky Way galaxy. These black hole engines are thought to be powered by magnetic fields. If the black hole is spinning, it can generate strong jets that blast across thousands of light-years and shape entire galaxies. But the supermassive black holes at the centers of galaxies are more like cosmic engines, converting energy from infalling matter into intense radiation that can outshine the combined light from all surrounding stars. Most people think of black holes as giant vacuum cleaners sucking in everything that gets too close. In contrast, other regions showed a much more organized pattern, possibly in the region where jets (shown by the narrow yellow streamer) would be generated. It found the fields in the disk to be disorderly, with jumbled loops and whorls resembling intertwined spaghetti. The Event Horizon Telescope has measured those magnetic fields for the first time with a resolution six times the size of the event horizon (6 Schwarzschild radii). Image: In this artist's conception, the black hole at the center of our galaxy is surrounded by a hot disk of accreting material.
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