The Breakthrough Listen Search for Intelligent Life: Observations of 1327 Nearby Stars over 1.10-3.45 GHz

Brief

Price et al. (2020) report results from 2016–2019 observations of 1,327 stellar targets using the 100-m Green Bank Telescope (L- and S-band, 1.10–2.80 GHz) and the 64-m CSIRO Parkes telescope (10-cm receiver, 2.60–3.45 GHz), totaling roughly 1,527 hours of on-sky time and ~219 TB of archived data. The turboSETI dedoppler algorithm searched for narrowband drifting signals at S/N ≥ 10 across ±4 Hz s⁻¹ drift rates, yielding 51.71 million raw hits compressed to 6,154 event groups and ultimately zero candidates surviving visual RFI vetting. The survey improves on the prior Enriquez et al. (2017) 692-star result by lowering the S/N threshold from 25 to 10, expanding drift-rate coverage from ±2 to ±4 Hz s⁻¹, and adding S-band and Parkes 10-cm coverage. All data are publicly available as part of Breakthrough Listen Data Release 1.

Metadata

Category

Search

Venue

The Astronomical Journal

Type

Peer-reviewed

Year

2020

Authors

Danny C. Price, J. Emilio Enriquez, Bryan Brzycki, Steve Croft, Daniel Czech, David DeBoer, Julia DeMarines, Griffin Foster, Vishal Gajjar, Nectaria Gizani, Greg Hellbourg, Howard Isaacson, Brian Lacki, Matt Lebofsky, David H. E. MacMahon, Imke de Pater, Andrew P. V. Siemion, Dan Werthimer, James A. Green, Jane F. Kaczmarek

DOI

10.3847/1538-3881/ab65f1

arXiv

1906.07750

Access

Open access

Length

2.1 M

Programs

Breakthrough Listen

Instruments

Green Bank Telescope (GBT) L-band 1.10–1.90 GHz, Green Bank Telescope (GBT) S-band 1.80–2.80 GHz, CSIRO Parkes 64-m 10-cm receiver 2.60–3.45 GHz

Data sources

Hipparcos catalog, Gliese catalog, RECONS catalog, Breakthrough Listen Data Release 1 (DR1)

Tags

SETI, technosignature, narrowband radio, radio survey, stellar survey, RFI mitigation

Key points

• 1,327 distinct primary stellar targets observed; 1,138 at GBT (749 at both L- and S-band), 189 at Parkes, drawn from the Isaacson et al. (2017) 1,702-star sample based on the Gliese, RECONS, and Hipparcos catalogs.p.2
• 51.71 million total turboSETI hits across all three receivers collapsed to 21,117 ON-only events, 6,154 event groups, and zero final candidates after visual inspection.p.7
• EIRP upper limits set at 2.1 × 10¹² W for GBT and 9.1 × 10¹² W for Parkes, roughly an order of magnitude below the prior Enriquez et al. (2017) limit of >10¹³ W for 692 stars.p.1
• Observing cadence: each target received three 5-minute ON and three 5-minute OFF pointings (30 minutes total), with signals required to appear in all three ON observations and absent from OFF pointings to pass event selection.p.3
• At L-band, GPS (1.155–1.196 GHz, 1.555–1.596 GHz) and GLONASS (1.592–1.619 GHz, 1.192–1.212 GHz) satellites dominated the RFI environment and accounted for the majority of high-density hit regions.p.7
• Parkes 10-cm observations showed only 60 event groups from 20 stars passing selection criteria, predominantly in the 3.40–3.45 GHz band attributed to Australian National Broadband Network interference.p.7
• ~219 TB of data products released publicly as BL Data Release 1 (DR1); 142 TB from Green Bank, 77 TB from Parkes.p.4
• The turboSETI tree search algorithm reduces computation from O(n²) to O(n log₂ n) by reusing redundant calculations across similar drift-rate slopes.p.6

Verbatim

• “After excluding events with characteristics consistent with terrestrial radio interference, we are left with zero candidates.”

  p.1

• “These observations constitute the most comprehensive search over 1.10–3.45 GHz for technosignatures to date.”

  p.1

• “Radio searches for extraterrestrial intelligence (ETI) have been ongoing since the 1960s (Drake 1961).”

  p.2

• “A majority of hits (21.90M) are at zero drift, a large fraction (13.9M) have negative drift rates, and a smaller fraction (1.37M) have positive drift rates.”

  p.7

• “The bias of signals toward negative drift rates is likely due to satellites in non-geosynchronous orbits, which accelerate with respect to the telescope (Zhang et al. 2006).”

  p.7

Most interesting

• 51.71 million raw signal detections were winnowed to exactly zero credible candidates, a reduction by a factor of more than 50 million through RFI vetting.
• Approximately 20% of all annual GBT observing time was dedicated to Breakthrough Listen during this campaign, making it one of the telescope's largest single science programs.
• The instantaneous bandwidth of SETI digital backends has expanded by a factor of 10⁸, from hundreds of hertz at Drake's 1961 Project Ozma to tens of gigahertz today, in roughly 40 years.
• Parkes conducted multiple epochs per target partly on the hypothesis that a transmitter on a rotating body would be intermittent, improving interception probability with repeated visits.
• Six recently discovered brown dwarfs and ultra-cool stars within 5 pc, including two WISE Y1-type objects at just 2.0 pc, were added to the Parkes sample beyond the standard Isaacson et al. catalog.
• The S-band hit distribution showed anomalous peaks at ±3.5 Hz s⁻¹ near 1930.2 MHz, consistent with cellular band RFI from cell phones near the Green Bank Observatory despite its federally protected Radio Quiet Zone.