Repeated signals from the center of the Milky Way could be aliens saying hello, new study claims

By Stephanie Pappas

June 8, 2023

A new search for extraterrestrial life has scientists looking inward — toward the center of our galaxy.

alien craft.jpeg
A hypothetical alien craft transmits radio signals into space. Scientists are on the hunt for signals like these.(Image credit: Breakthrough Listen / Danielle Futselaar)
Could intelligent aliens be lurking at the heart of the Milky Way?

A new search for extraterrestrial life aims to find out by listening for radio pulses from the center of our galaxy. Narrow-frequency pulses are naturally emitted by stars called pulsars, but they're also used deliberately by humans in technology such as radar. Because these pulses stand out against the background radio noise of space, they're an effective way of communicating across long distances — and an appealing target to listen for when searching for alien civilizations.

Scientists described the alien-hunting strategy in a new study, published May 30 in The Astronomical Journal. Researchers led by Cornell University graduate student Akshay Suresh developed software to detect these repetitive frequency patterns and tested it on known pulsars to be sure it could pick up the narrow frequencies. These frequency ranges are very small, at about a tenth of the width of frequencies used by a typical FM radio station. The researchers then searched data from the Green Bank Telescope in West Virginia using the method.

"Until now, radio SETI has primarily dedicated its efforts to the search for continuous signals," study coauthor Vishal Gajjar of the SETI Institute, a nonprofit organization dedicated to the search for intelligent life in the universe, said in a statement. "Our study sheds light on the remarkable energy efficiency of a train of pulses as a means of interstellar communication across vast distances. Notably, this study marks the first-ever comprehensive endeavor to conduct in-depth searches for these signals."

The researchers are listening in to the middle of the Milky Way because it is dense with stars and potentially habitable exoplanets. What's more, if intelligent aliens at the core of the Milky Way wanted to reach out to the rest of the galaxy, they could send signals sweeping across a wide array of planets, given their privileged position at the center of the galaxy. Using narrow bandwidths and repeated patterns would be a prime way for aliens to reveal themselves, as such a combination is extremely unlikely to occur naturally, study co-author Steve Croft, a project scientist with the Breakthrough Listen program, said in a separate statement.

The method uses an algorithm that can search through 1.5 million telescope data samples in 30 minutes. Though researchers did not find any telltale signs in their first search, they say that the speed of the algorithm will help improve searches in the future.

"Breakthrough Listen captures huge volumes of data, and Akshay’s technique provides a new method to help us search that haystack for needles that could provide tantalizing evidence of advanced extraterrestrial life forms," Croft said.


Here's exerpts from the original paper from the Astronomical Journal:

A 4–8 GHz Galactic Center Search for Periodic Technosignatures​

by Akshay Suresh1,2, Vishal Gajjar2,3, Pranav Nagarajan2,4,5, Sofia Z. Sheikh2,3, Andrew P. V. Siemion2,3,6,7, Matt Lebofsky2, David H. E. MacMahon2, Danny C. Price2,8, and Steve Croft2,3.

1 Cornell Center for Astrophysics and Planetary Science, and Department of Astronomy, Cornell University, Ithaca, NY 14853, USA;
2 Breakthrough Listen, University of California, Berkeley, CA 94720, USA
3 SETI Institute, 339 N Bernardo Ave Suite 200, Mountain View, CA 94043, USA
4 Department of Astronomy, University of California, Berkeley, CA 94720, USA
5 Cahill Center for Astronomy and Astrophysics, MC 249-17, California Institute of Technology, Pasadena, CA 91125, USA 6 Department of Astrophysics/IMAPP, Radboud University, Nijmegen, The Netherlands
7 University of Malta, Institute of Space Sciences and Astronomy, Malta
8 International Centre for Radio Astronomy Research, Curtin University, WA 6102, Australia

Received 2023 January 18; revised 2023 April 10; accepted 2023 April 12; published 2023 May 30

Radio searches for extraterrestrial intelligence have mainly targeted the discovery of narrowband continuous-wave beacons and artificially dispersed broadband bursts. Periodic pulse trains, in comparison to the above technosignature morphologies, offer an energetically efficient means of interstellar transmission. A rotating beacon at the Galactic Center (GC), in particular, would be highly advantageous for galaxy-wide communications. Here, we present blipss, a CPU-based open-source software that uses a fast folding algorithm (FFA) to uncover channel-wide periodic signals in radio dynamic spectra. Running blipss on 4.5 hr of 4–8 GHz data gathered with the Robert C. Byrd Green Bank Telescope, we searched the central
$6^{\prime} $
of our galaxy for kHz-wide signals with periods between 11 and 100 s and duty cycles (δ) between 10% and 50%. Our searches, to our knowledge, constitute the first FFA exploration for periodic alien technosignatures. We report a nondetection of channel-wide periodic signals in our data. Thus, we constrain the abundance of 4–8 GHz extraterrestrial transmitters of kHz-wide periodic pulsed signals to fewer than one in about 600,000 stars at the GC above a 7σ equivalent isotropic radiated power of ≈2 × 1018 W at δ ≃ 10%. From an astrophysics standpoint, blipss, with its utilization of a per-channel FFA, can enable the discovery of signals with exotic radio frequency sweeps departing from the standard cold plasma dispersion law.

The Search for Extraterrestrial Intelligence (SETI); review: Tarter 2001) is an active quest to find evidence of advanced alien life in the universe through signatures of their technologies. Radio SETI has been ongoing since the early 1960s (Drake 1960). Two broad categories of potential radio extraterrestrial intelligence (ETI) signals are intentional beacon emissions (Cocconi & Morrison 1959; Drake & Sagan 1973; Tarter et al. 1980; Valdes & Freitas 1986; Steffes & Deboer 1994; Mauersberger et al. 1996) and leakage radiation emanating from alien technologies (Guillochon & Loeb 2015; Benford & Benford 2016). Of these two technosignatures, the spectrotemporal characteristics of the latter are much harder to speculate. In addition, such leakage signals are likely to be weaker. Hence, modern radio SETI efforts have primarily focused on wideband searches for deliberate narrowband (Δν ∼ 1 Hz) Doppler-drifting beacons from Galactic planetary systems (Siemion et al. 2013; Harp et al. 2016; Tingay et al. 2016; Enriquez et al. 2017; Gray & Mooley 2017; Margot et al. 2018, 2021; Pinchuk et al. 2019; Price et al. 2020; Gajjar et al. 2021; Lacki et al. 2021; Traas et al. 2021; Franz et al. 2022; Garrett & Siemion 2023; Tusay et al. 2022) and neighboring galaxies (Gray & Mooley 2017; Lacki et al. 2021; Garrett & Siemion 2023).

Of all directions in the sky, the line of sight toward the Galactic Center (GC) offers the greatest propensity for the emergence of intelligent life (Gajjar et al. 2021). Further, radial beacons from the GC are viable given their advantageous positioning for galaxy-wide communications (Benford et al. 2010). Thus, the GC is an ideal first target for our periodic technosignature searches. Section 3 describes our 4–8GHz observations undertaken as part of the Breakthrough Listen(BL) GC survey (Gajjar et al. 2021). We detail the methodology of blipss in Section 4. In Section 5, we present the findings obtained from running blipss on our GC data. Section 6 highlights the implications of our study with emphasis on its potential outstanding gains for SETI.

Radio SETI has hitherto focused on the discovery of narrowband CW signals and artificially dispersed broadband pulses from extraterrestrial worlds. In contrast to these technosignature morphologies, periodic spectral signals offer an energetically efficient means of transmission across vast interstellar distances. A rotating beacon at the GC is, in particular, advantageously placed for galaxy-wide communications.

Here, we present blipss, a CPU-based software package to enable FFA searches for periodic spectral signals from alien worlds. Operating on radio dynamic spectra, blipss conducts FFA searches on a per-channel basis, thereby permitting periodicity detection regardless of signal bandwidth and dispersion. Consequently, blipss can uncover signals with exotic swept frequency structures frequently missed by traditional broadband pulse search techniques that assume cold plasma dispersion. Running blipss on 4.5 hr of data from the 4–8 GHz BLGC survey, we report a nondetection of periodic pulsed signals with P ä [11 s, 100 s] and δ ä [10%, 50%]. Thus, our investigations constrain the abundance of 4–8 GHz extraterrestrial transmitters of kHz-wide periodic spectral signals to fewer than one in about 600,000 stars at the GC above a 7σ18 of routines in blipss and incorporation of coherent voltage folding to expand our search space of periodic signals. Progress on the former will enable integration of blipss into real-time search pipelines for large-scale event discovery and follow up.

Breakthrough Listen is managed by the Breakthrough Initiatives, sponsored by the Breakthrough Prize Foundation. P.N. was funded as a participant in the Berkeley SETI Research Center Research Experience for Undergraduates Site, sup- ported by the National Science Foundation under grant No. 1950897. S.Z.S. acknowledges that this material is based upon work supported by the National Science Foundation MPS- Ascend Postdoctoral Research Fellowship under grant No.2138147. The Green Bank Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Facility: GBT. Software: Astropy (Astropy Collaboration et al. 2013, 2018), Blimpy (Price et al. 2019), blipss (this work), Matplotlib (Hunter 2007), NumPy (Van der Walt et al. 2011), Python 3 (, Pandas (Wes McKinney 2010; Pandas development team 2022), riptide-ffa (Morello et al. 2020) SciPy (Virtanen et al. 2020).

For the complete work, see:

The Breakthrough Listen Investigation for Periodic Spectral Signals (BLIPSS), led by Akshay Suresh, Cornell doctoral candidate in astronomy, is pioneering a search for periodic signals emanating from the core of our galaxy, the Milky Way. The research aims to detect repetitive patterns, a way to search for extraterrestrial intelligence (SETI) within our cosmic neighborhood. The researchers developed software based on a Fast Folding Algorithm* (FFA), an efficient search method offering enhanced sensitivity to periodic sequences of narrow pulses. Their paper, “A 4–8 GHz Galactic Center Search for Periodic Technosignatures,” was published May 30 in The Astronomical Journal.

*Fast Folding Algorithm (FFA): fast folding algorithm (FFA), is an alternative pulsar searching technique to the fast Fourier transform (FFT). Weaknesses in the FFT, including a susceptibility to red noise, leave it insensitive to pulsars with long rotational periods (P > 1 s). This sensitivity gap has the potential to bias our understanding of the period distribution of the pulsar population. The FFA, a time-domain based pulsar searching technique, has the potential to overcome some of these biases. Modern distributed-computing frameworks now allow for the application of this algorithm to all-sky blind pulsar surveys for the first time. However, many aspects of the behaviour of this search technique remain poorly understood, including its responsiveness to variations in pulse shape and the presence of red noise. Using a custom CPU-based implementation of the FFA, FFANCY**, we have conducted an in-depth study into the behaviour of the FFA in both an ideal, white noise regime as well as a trial on observational data from the High Time Resolution Universe South Low Latitude pulsar survey, including a comparison to the behaviour of the FFT. We are able to both confirm and expand upon earlier studies that demonstrate the ability of the FFA to outperform the FFT under ideal white noise conditions, and demonstrate a significant improvement in sensitivity to long-period pulsars in real observational data through the use of the FFA.


FFANCY: A pulsar searching software package designed for testing of and experimentation with the Fast Folding Algorithm (FFA). Developed by Andrew Cameron, MPIfR IMPRS PhD research student, in collaboration with Ewan Barr & David Champion. FFANCY is self contained, and requires only standard external C libraries for installation. Simply run 'make all' and the full set of executables will be compiled in the root directory.

Last edited:
Actual signals from sentient beings "in the center of the Milky Way" would be of great interest, and make scientists absolutely giddy, but what actual good would it be for us? Those signals would have been broadcast 30,40, 50 thousand years ago! Unless we suddenly learn to travel through space/time at speeds deemed impossible by Einstein, we'll never get to another habitable planet before we send ourselves to extinction, anyway.
Ah, Thomas Thompson, you have nailed the primary problem with SETI.

Should we catch an intelligent message floating through interstellar space from more than a dozen light years away (just an example), your return message will require at least a 24 year turn around. Will the line be kept open by proper funding for 24 years? I believe this possibility is doubtful.