The First Very Long Baseline Interferometric SETI Experiment

TL;DR

This paper demonstrates that Very Long Baseline Interferometry (VLBI) can effectively discriminate between extraterrestrial signals and terrestrial interference, providing a new targeted approach for SETI with potential for future large-scale arrays.

Contribution

It presents the first VLBI-based SETI experiment, showing its efficiency in identifying genuine extraterrestrial signals and establishing upper limits on potential alien transmitters.

Findings

222 potential signals detected and ruled out as RFI

Upper limit of 7 MW/Hz on alien emitter power in Gliese 581

VLBI is effective for targeted SETI and scalable to future arrays

Abstract

The first Search for Extra-Terrestrial Intelligence (SETI) conducted with Very Long Baseline Interferometry (VLBI) is presented. By consideration of the basic principles of interferometry, we show that VLBI is efficient at discriminating between SETI signals and human generated radio frequency interference (RFI). The target for this study was the star Gliese 581, thought to have two planets within its habitable zone. On 2007 June 19, Gliese 581 was observed for 8 hours at 1230-1544 with the Australian Long Baseline Array. The dataset was searched for signals appearing on all interferometer baselines above five times the noise limit. A total of 222 potential SETI signals were detected and by using automated data analysis techniques, were ruled out as originating from the Gliese 581 system. From our results we place an upper limit of 7 MW/Hz on the power output of any isotropic emitter located in the Gliese 581 system, within this frequency range. This study shows that VLBI is ideal for targeted SETI, including follow-up observations. The techniques presented are equally applicable to next-generation interferometers, such as the long baselines of the Square Kilometre Array (SKA).