The Breakthrough Listen Search for Intelligent Life: Technosignature Search of 97 Nearby Galaxies (2312.03943v1)

Abstract: The Breakthrough Listen search for intelligent life is, to date, the most extensive technosignature search of nearby celestial objects. We present a radio technosignature search of the centers of 97 nearby galaxies, observed by Breakthrough Listen at the Robert C. Byrd Green Bank Telescope. We performed a narrowband Doppler drift search using the turboSETI pipeline with a minimum signal-to-noise parameter threshold of 10, across a drift rate range of $\pm$ 4 Hz\ $s^{-1}$, with a spectral resolution of 3 Hz and a time resolution of $\sim$ 18.25 s. We removed radio frequency interference by using an on-source/off-source cadence pattern of six observations and discarding signals with Doppler drift rates of 0. We assess factors affecting the sensitivity of the Breakthrough Listen data reduction and search pipeline using signal injection and recovery techniques and apply new methods for the investigation of the RFI environment. We present results in four frequency bands covering 1 -- 11 GHz, and place constraints on the presence of transmitters with equivalent isotropic radiated power on the order of $10^{26}$ W, corresponding to the theoretical power consumption of Kardashev Type II civilizations.

• The paper employs a narrowband Doppler drift search using the turboSETI pipeline across four frequency bands to detect radio technosignatures in 97 galaxies.
• The paper utilizes an 'on-off' observational cadence with the Green Bank Telescope to mitigate terrestrial interference while processing 139.7 TB of data.
• The paper constrains extraterrestrial signal detections by placing an upper limit of 3.1% for galaxies that could host civilizations transmitting high-power signals.

Overview of "The Breakthrough Listen Search for Intelligent Life: Technosignature Search of 97 Nearby Galaxies"

The paper "The Breakthrough Listen Search for Intelligent Life: Technosignature Search of 97 Nearby Galaxies" presents an extensive investigation into radio technosignatures originating from 97 nearby galaxies. This paper was conducted using the Robert C. Byrd Green Bank Telescope as part of the Breakthrough Listen Initiative. The primary objective is to detect signs of extraterrestrial intelligence by identifying artificial signals distinct from natural cosmic phenomena.

The approach centered around a narrowband Doppler drift search utilizing the turboSETI pipeline across four frequency bands ranging from 1 to 11 GHz. The observational campaign aimed to detect continuous, narrowband signals with drift rates within ±4 Hz/s and signal-to-noise ratios above a threshold of 33. These parameters are strategically chosen to maximize the potential identification of signals indicative of technologically capable extraterrestrial civilizations, especially those characterized by high-power emissions comparable to a Kardashev Type II civilization.

Methodological Insights

The survey utilized a cadence strategy wherein each galaxy was observed through an "on-off" pattern to mitigate interference from Earth-originated signals. This methodical approach enabled the discrimination of celestial signals from terrestrial RFI. The substantial volume of data, amounting to 139.7 TB, underscores the scale of the search and the computational resources dedicated to processing this information.

The authors also conducted a thorough sensitivity analysis of the turboSETI pipeline, highlighting performance characteristics such as dechirping efficiency and noise calculation discrepancies. These analyses are integral to understanding the limits and capabilities of the detection system, informing future refinements in the search algorithms.

Results and Analysis

Despite the comprehensive search across four bands and hundreds of hours of observation, no compelling technosignature candidates that could not be attributed to RFI were identified. The findings therefore place upper constraints on the possibility of detectable high-power transmissions from extraterrestrial sources within the surveyed galaxies. Specifically, the analysis suggests that less than 3.1% of the surveyed galaxies could host civilizations broadcasting at power levels detectable by current methodologies. This result largely stems from the vast distances involved and cosmic attenuation effects, such as interstellar scintillation, which can modulate signal visibility.

Implications and Future Directions

The research delineates strong implications for technosignature search strategies. It reinforces the importance of considering interstellar and intergalactic scattering effects that affect signal detectability. Furthermore, it suggests that future searches could benefit from adaptive observation strategies, possibly incorporating redundancy or machine learning for enhanced signal classification and noise differentiation.

The paper also underscores the need for innovative methodologies that can circumvent limitations such as those imposed by spectral leakage and high RFI environments. Future developments might include algorithmic enhancements or the use of larger arrays for increased sensitivity.

Conclusion

This paper represents one of the most extensive searches for technosignatures in nearby galaxies, significantly contributing to our understanding and approach towards identifying extraterrestrial intelligence. Although no technosignatures were detected, the work lays the groundwork for future explorations by refining search parameters and elucidating the environmental and methodological challenges intrinsic to such an ambitious endeavor.