Searching for Intelligent Life in Gravitational Wave Signals Part I: Present Capabilities and Future Horizons

Abstract

We show that the Laser Interferometer Gravitational Wave Observatory (LIGO) is a powerful instrument in the Search for Extra-Terrestrial Intelligence (SETI). LIGO's ability to detect gravitational waves (GWs) from accelerating astrophysical sources, such as binary black holes, also provides the potential to detect extra-terrestrial mega-technology, such as Rapid And/or Massive Accelerating spacecraft (RAMAcraft). We show that LIGO is sensitive to RAMAcraft of \(1\) Jupiter mass accelerating to a fraction of the speed of light (e.g. \(10\%\)) up to about \(100\,{\rm kpc}\). Existing SETI searches probe on the order of thousands to tens of thousands of stars for human-scale technology (e.g. radiowaves), whereas LIGO can probe all \(10^{11}\) stars in the Milky Way for RAMAcraft. Moreover, thanks to the \(f^{-1}\) scaling of the GW signal produced by these sources, our sensitivity to these objects will increase as low-frequency, space-based detectors are developed and improved. In particular, we find that DECIGO and the Big Bang Observer (BBO) will be about 100 times more sensitive than LIGO, increasing the search volume by 10\(^{6}\). In this paper, we calculate the waveforms for linearly accelerating RAMAcraft in a form suitable for LIGO, Virgo, or KAGRA searches and provide the range for a variety of possible masses and accelerations. We expect that the current and upcoming GW detectors will soon become an excellent complement to the existing SETI efforts.