SETI

Searching for Technologically Advanced Extraterrestrial Life

Are we alone in the Universe? Longing to find evidence of extraterrestrial life has been at the centre of the quest to know our place in the Cosmos.
While efforts are underway at a large scale to detect biosignatures, finding unambiguous signs of technologically advanced extraterrestrial life or technosignature is likely to be the single most significant event in the history of science. For the past six decades, radio technosignature searches have focused on searching for just one morphological type of signal (i.e. narrowband signal). Limitations in computing power and the flexibility of radio observatories in providing access to the rawest forms of the collected data, impede searches encompassing all the possible signal types including completely agnostic types of anomalies we are unable to envision.

My research on this topic focused on developing novel Artificial Intelligence and GPU-based tools to search for unique classes of previously unexplored morphological class of signals. With the Breakthrough Listen program, I am PI of the 600-hours of deep survey of the Galactic Center across 1 to 100 GHz to search for these signals from world's largest radio telescopes. I also work with around half a dozen radio observatories to deploy cutting-edge digital instruments and help enable observatory-focused unique observing programs for technosignatures.

Top three research highlights on this topic are below.

Searching for Artificially dispersed pulses

For the past six decade, the search for extraterrestrial intelligence at radio frequencies has largely been focused on continuous-wave narrowband signals. In Gajjar et al. (2022) demonstrate that broadband pulsed beacons are energetically efficient compared to the narrowband beacons over longer operational timescales (see image). In Gajjar et al. (2022), we report the first extensive survey searching for such broadband pulsed beacons towards close to 2000 stars with the GBT. We report a detailed search leveraging a convolutional neural network classifier on high-performance GPUs deployed for the very first time in a large-scale search for signals from extraterrestrial intelligence. Using this classifier, we were able to reduce the number of false positives by 97%. Our selection criteria did not return any signals-of-interest. We thus place a constraint on the existence of broad- band pulsed beacons in our solar neighborhood: <1 in 1000 stars have transmitter power-densities >10^5 W/Hz.

I was so happy to see Evan Lewis did a nice blog on this article in Astrobites.

Gajjar et al. 2022

Galactic Center

A line of sight toward the Galactic Center (GC) offers the largest number of potentially habitable systems of any direction in the sky. In Gajjar et al. (2021), we demonstrated that a line-of-sight towards the GC has the highest number density of habitable planets within the Galaxy (see side image). The GC is a natural cynosure of the entire Milky Way Galaxy and is also suggested to be an ideal `Schelling point' to place a powerful transmitter. I am leading a 600-hours deep survey of the region using the GBT, SRT, and Parkes as a part of the Breakthrough Listen program. In Gajjar et al. (2021), we outlined our observing strategies with of deep observations across 1 to 100 GHz. We reported preliminary results from our survey for extraterrestrial intelligence (ETI) beacons. With our narrowband drifting signal search, we were able to place meaningful constraints on ETI transmitters with transmitter power of ≥ 10^18 W among 60 million stars. For the first time, we were able to constrain the existence of artificially dispersed transient signals with output power ≥1 × 10^14 W/Hz and repetition period ≤10 hrs. This is the first time Galactic Center has been searched for such signals.

I was so proud to see the Alice Curtin wrote a nice blog in Astrobites about this paper.

The data generated from the survey also enabled a number of ancillary studies published in the following papers

Gajjar et al. 2021 Study of J1745-2900 Searching for Axions Searching for Pulsars at the Galactic Center

Opportunities to search for extraterrestrial intelligence with the FAST

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the largest single-aperture radio telescope in the world, and is well positioned to conduct sensitive searches for radio emission indicative of activities of technologically advanced extraterrestrial life. SETI is one of the five key science goals specified in the original FAST project plan. A collaboration with the Breakthrough Listen Initiative was initiated in 2016 with a joint statement signed both by Dr. Jun Yan, the then director of National Astronomical Observatories, Chinese Academy of Sciences (NAOC), and Dr. Peter Worden, Chairman of the Breakthrough Prize Foundation. In this paper, we high- light some of the unique features of FAST that will allow for novel SETI observations. We identify and describe three different signal types indicative of a technological source, namely, narrow band, wide-band artificially dispersed and modulated signals. Here, we propose observations with FAST to achieve sensitiv- ities never before explored. For nearby exoplanets, such as TESS targets, FAST will be sensitive to an EIRP of 1.9 × 1011 W, well within the reach of current human technology. For the Andromeda Galaxy, FAST will be able to detect any Kardashev type II or more advanced civilization there.

Li & Gajjar et al. 2019