New approach to very-high-resolution astronomical imaging

Astronomical objects are very distant, and so the angular sizes of many astrophysical phenomena are much smaller than can be resolvedwith conventional telescopes. Optical interferometry allows us to explore very small angular scales. Michelson and Pease first used interferometric observations nearly a century ago to measure the stellar diameter of Betelgeuse.1 Since then, more than a dozen interferometers have been built worldwide to characterize the sizes and motions of stars and their environments. However, advances in technology have only recently allowed us to reconstruct physically realistic images of these objects rather than merely providing simple size measurements. We are ambitious in building the Magdalena Ridge Observatory Interferometer (MROI), with a mission centered on one primary goal: producing very-high-resolution images of faint astronomical targets.2 Stellar interferometry works by combining the light from multiple telescopes to form interference fringes. This requires a complex optical system involving multiple light reflections from the light-collecting surfaces to the detectors measuring these fringes. Each reflection adds aberrations to the observed signal and results in photon loss. For other interferometers, often more than 40 reflections are required before the interference fringes are measured. The MROI design minimizes the number of reflections to only 21, allowing scientists to observe much fainter targets than previously accomplished. In addition, the interferometer design (see Figure 1) capitalizes on having small-diameter (1.4m) movable telescopes, so that the array can be reconfigured easily to match the resolution needed for observations of a particular target, much like the operation of our larger radio counterpart, the Very Large Array. Figure 1. Architectural rendering of the now-completed Magdalena Ridge Observatory Interferometer (MROI) delay-line facility and beam-combining laboratory (as well as the as-yet-unfinished telescopes) atop Magdalena Ridge. The telescopes will be movable onto 28 pads, with separations ranging from 7.5 to 340m.