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Eavesdropping on interstellar communications with the Green Bank Telescope

Photo of the Green Bank Telescope at night by Dave Green.

Communications across the vastness of interstellar space could be enhanced by taking advantage of a star’s ability to focus and magnify communication signals. A team of graduate students at Penn State is looking for just these sorts of communication signals that might be taking advantage of our own sun if transmissions were passing through our solar system.

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Continuum Observing with the GBT

There are two instruments on the GBT specifically designed for carrying out sensitive continuum observations: (1) Mustang-2 which is a bolometer array operating at 90 GHz, and (2) Ka-band with the Caltech Continuum Backend (CCB) which operates over 26-38GHz. Continuum observations are available with other GBT receivers, but are limited by the 1/f noise. GBT Memo#282 provides the performance of the GBT receivers for continuum observations. This memo provides the maximum effective bandwidth for each receiver. For mapping extended regions, the effective bandwidth [BWeff] is smaller than the bandwidth given in GBT Memo#282 [BWeff(max)] based on the time scale between the ON and OFF/reference observations. Depending on the time scale (t) between the ON and OFF/reference observations (or time to map over a region of interest), the BWeff = BWeff(max) (0.2 sec/t), where the time (t) is in seconds. The continuum sensitivity can be estimated using the sensitivity calculator by selecting a bandwidth (e.g., in spectral-line mode) that matches the 1/f noise effective bandwidth. This is the minimum noise level that can be reached by a single observation. Improvements can be made by making multiple observations (the noise integrates down as (1/N)0.5 where N is the number of independent observations). Thus, for continuum observations it is important to take many short observations and to carry out fast mapping scans for imaging.

Please contact a GBT scientist if you have any questions.