A recent study led by researchers Bo-Lun Huang, Zhen-Zhao Tao, and Tong-Jie Zhang has provided new insights into the presence of galaxy-scale waste heat, known as Dysonian signatures, in nearby galaxies. Utilizing data from the Wide-field Infrared Survey Explorer (WISE), the team has established upper limits on the bolometric waste heat luminosity of these galaxies, significantly contributing to the field of astrophysics.
The study begins with the 2MASS Redshift Survey (2MRS) and employs a methodical cross-matching process with both CatWISE2020 and AllWISE datasets. By applying standard mid-infrared (MIR) active galactic nucleus (AGN) and starburst vetoes, researchers treated WISE bands W1 and W2 as stellar baselines, while W3 and W4 served as constraining bands. This approach allowed the team to calculate conservative 3-sigma upper limits on the waste heat luminosity for temperatures ranging from 150 K to 600 K.
Key Findings on Waste Heat Luminosity
The analysis revealed that the median caps on bolometric waste heat luminosity across the specified temperature range were approximately 5-9 x 10^8 L_sun. This finding indicates a significant amount of energy potentially being emitted as waste heat from these galaxies. When aggregating data at the population level, the study found a one-sided 95% upper bound on the fraction of nearby galaxies that could host waste heat exceeding a specific threshold. This fraction decreases monotonically with increasing threshold, reaching an asymptote of about 1/6500 at higher thresholds, which is set by the sample size.
The research emphasizes that sensitivity transitions from W4 at a temperature of 300 K. Using the AGENT formalism, the authors calculated that a typical Milky Way-like galaxy with a stellar luminosity of 3 x 10^10 L_sun would imply average caps of waste heat representing approximately 21% of its stellar luminosity at around 300 K.
Methodology and Implications
The methodology employed in this study included a detailed analysis of the WISE W1-W2 versus W2-W3 color-color diagram, which illustrated how the MIR AGN and starburst rejection interacted with plausible galaxy-scale waste heat spectral energy distributions. This form of analysis is crucial for identifying and understanding the energy dynamics of galaxies and contributes to the broader search for extraterrestrial intelligence (SETI).
The findings, which span 18 pages and include 12 figures and 2 tables, have been accepted for publication in The Astronomical Journal. The research was submitted on January 12, 2026, and is expected to enhance our understanding of the energy outputs of galaxies and their potential implications for the search for advanced extraterrestrial civilizations.
As scientists continue to explore the cosmos, studies like this one shed light on the intricate processes that govern galaxy behavior, reinforcing the significance of waste heat as a potential indicator of technological activity in the universe.
