Building the Event Horizon Telescope: Observing Black Holes with Schwarzschild Radius Resolution

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There is a massive black hole at the center of our galaxy, and similar objects at the centers of other galaxies, objects that distort spacetime by the strength of their immense gravitational fields. Spatially, a black hole is phenomenally compact. Nonetheless, Dr. Doeleman and his colleagues, utilizing the combined millimeter-wave radio signals from an array of radiotelescopes located on different continents, will image the event horizon of a black hole. The combination of high frequency and long interferometer baselines will produce an unprecedented high spatial resolution, and this project presents a scientifically compelling way to utilize it.The project will develop broadband very-long-baseline interferometry (VLBI) instrumentation matched to the millimeter- and submillimeter-wave receivers now in use at radiotelescopes suitable for use in the intercontinental array. With commercially available digital signal processing devices incorporated into custom systems, the instrumentation to be built will achieve 8 GHz of bandwidth in each polarization. That broad bandwidth is critical for maximizing system sensitivity. The resulting VLBI network will achieve, at 1.3 mm wavelength, tens of microarcseconds of angular resolution on the sky. Earlier observations by this team have measured structure on the scale of the Schwarzschild radius of the black hole at the center of our galaxy, and this project plans to observe and image the actual black hole event horizon.The hardware developed under this program will be made available to the astronomy community. High-school teachers, undergraduates, graduate students, and postdoctoral fellows will be involved in the research program. Valuable hands-on training in instrumentation will be provided that will be valuable on other modern radiotelescopes. Funding for this project is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.