Highest resolution imaging in astronomy is achieved by interferometry,connecting telescopes over increasingly longer distances, and at successivelyshorter wavelengths. Here, we present the first diffraction-limited images invisual light, produced by an array of independent optical telescopes, connectedelectronically only, with no optical links between them. With an array of smalltelescopes, second-order optical coherence of the sources is measured throughintensity interferometry over 180 baselines between pairs of telescopes, andtwo-dimensional images reconstructed. The technique aims at diffraction-limitedoptical aperture synthesis over kilometre-long baselines to reach resolutionsshowing details on stellar surfaces and perhaps even the silhouettes oftransiting exoplanets. Intensity interferometry circumvents problems ofatmospheric turbulence that constrain ordinary interferometry. Since theelectronic signal can be copied, many baselines can be built up betweendispersed telescopes, and over long distances. Using arrays of air Cherenkovtelescopes, this should enable the optical equivalent of interferometric arrayscurrently operating at radio wavelengths.
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