A sharper view of our galaxy’s black hole

The spectacular jets that shoot from radio galaxies are fueled by plasma swirling around the galaxies’ central black holes. Because the black hole at the heart of the Milky Way has comparatively little fuel to draw on, the emission it engenders is feeble. Whether it sustains jets is uncertain. Still, thanks to the black hole’s relative proximity, astronomers hope to resolve the structures close to the event horizon that might be responsible for launching jets. With that and other goals in mind, Michael Johnson of the Harvard–Smithsonian Center for Astrophysics and his collaborators have observed the Milky Way’s center using the Event Horizon Telescope, an interferometric array of four millimeter-wavelength telescopes at sites in Arizona, California, and Hawaii. In the millimeter band, the emission from the center of the galaxy is dominated by synchrotron radiation from relativistic electrons spiraling around magnetic field lines. By measuring and mapping the radiation’s polarization,...