The Ĝ Infrared Search for Extraterrestrial Civilizations with Large Energy Supplies. III. The Reddest Extended Sources in WISE

Abstract: Nearby Type III (galaxy-spanning) Kardashev supercivilizations would have high mid-infrared (MIR) luminosities. We have used the Wide-field Infrared Survey Explorer (WISE) to survey ~$1 \times 10^5$ galaxies for extreme MIR emission, $10^3$ times more galaxies than the only previous such search. We have calibrated the WISE All-sky Catalog pipeline products to improve its photometry for extended sources. We present 563 extended sources with $|b| \ge 10$ and red MIR colors, having visually vetted them to remove artifacts. No galaxies in our sample host an alien civilization reprocessing more than 85% of its starlight into the MIR, and only 50 galaxies, including Arp 220, have MIR luminosities consistent with >50% reprocessing. Ninety of these (likely) extragalactic sources have little literature presence; in most cases they are likely barely resolved galaxies or pairs of galaxies undergoing large amounts of star formation. Five are new to science and deserve further study. The Be star 48 Librae sits within a MIR nebula, and we suggest that it may be creating dust. WISE, 2MASS, and Spitzer imagery shows that IRAS 04287+6444 is consistent with a previously unnoticed, heavily extinguished cluster of young stellar objects. We identify five "passive" (i.e. red) spiral galaxies with unusually high MIR and low NUV luminosity. We search a set of optically "dark" HI galaxies for MIR emission, and find none. These 90 poorly understood sources and five anomalous passive spirals deserve follow-up via both SETI and conventional astrophysics.

• The paper employs WISE survey techniques on over 100,000 galaxies to set upper limits on mid-infrared emissions from potential Type III civilizations.
• The study identifies 563 red MIR sources, ruling out cases with over 85% starlight reprocessed as indicators of advanced extraterrestrial technology.
• Key findings include five novel sources and the recommendation for future spectral energy distribution analyses to refine energy output constraints.

Overview of "The ^G Infrared Search for Extraterrestrial Civilizations with Large Energy Supplies. III. The Reddest Extended Sources"

The search for extraterrestrial intelligence (SETI) has long posed a fundamental question about the existence of advanced civilizations in the universe. This paper represents the third part of a series focusing on the infrared search for Type III Kardashev supercivilizations, which are hypothesized to utilize energy on a galaxy-wide scale. These civilizations would exhibit high mid-infrared (MIR) emissions due to the reprocessing of starlight into waste heat. The authors employ data from the Wide-field Infrared Survey Explorer (WISE) to conduct a large-scale survey targeting over 100,000 galaxies for anomalously high MIR output, significantly expanding upon the sample size of previous studies.

Key Methodologies and Findings

1. Survey Methodology: The researchers utilized the WISE all-sky catalog, focusing on extended sources with notably red MIR colors. They applied photometric calibration to enhance data reliability for extended sources and employed visual verification methods to remove artifacts and false detections. The result was the identification of 563 extended sources with high MIR colors, which were classified after comprehensive vetting processes.
2. Detection Results: The survey found no galaxies where an extraterrestrial civilization reprocessed more than 85% of its starlight into MIR emissions. Only 50 galaxies had MIR luminosity indicators consistent with >50% reprocessing. The majority of these sources were associated with natural phenomena such as starburst galaxies or active galactic nuclei.
3. Investigations of Novel Sources: Among the sources with little prior literature mention, five were found to be essentially new to science. These necessitate further study to determine their characteristics, with one particular cluster of sources showing no optical counterparts and presenting high interest.
4. Exploring Alternative Explanations: A hypothesis for the existence of certain extragalactic structures was considered, such as molecular clusters influenced by significant internal dust formations. However, no concrete evidence for a supercivilization was found.
5. Extended Implications: The paper provides a rigorous upper limit on the energy output of potential Type III civilizations in the local universe. It suggests that thorough spectral energy distribution (SED) analysis of the identified extreme galaxies could refine these upper limits further.

Implications and Future Directions

The absence of detectable high MIR emission attributable to extraterrestrial civilizations contextualizes current discussions on the rarity and visibility of advanced life in the universe. While this study rules out certain magnitudes of waste heat emissions in nearby galaxies, the question remains open, now further refined by these constraints.

In the field of astrophysics and SETI, the methodology applied here could inspire future investigations utilizing even more advanced infrared survey instruments, potentially probing deeper into obscured cosmic environments. Furthermore, cross-referencing this observational strategy with other wavelengths and advanced modeling techniques might uncover subtle signs of civilizations or confirm natural explanations with greater confidence.

Ultimately, this work paves the way for leveraging all-sky MIR surveys as a powerful tool to systematically approach the detection of galactic-scale technologies, contributing to the broader understanding of both natural astrophysical processes and the potential distribution of advanced life.