The light reaching us from those two galaxies left before multicellular life existed on Earth.
The distance to ILT J134649.72+542621.7 and ILT J145757.90+565323.8, the two LOFAR survey designations for the galaxies whose mid-infrared emission cannot be explained by any natural process the Chen-Garrett study could identify, means that whatever is producing the anomalous signal was already producing it when the most complex life on this planet was a colonial organism in a Precambrian ocean. The signal has been traveling toward us for longer than complex life has existed here. We have only just developed the instruments to detect it.
Hongjing Chen and Michael Garrett published their analysis in the Monthly Notices of the Royal Astronomical Society after examining 21 galaxies identified in the LOFAR survey as having elevated mid-infrared emission. Four of those galaxies showed mid-infrared radiation amplified by a factor of ten above what the radio-infrared correlation predicts. Two of the four were identified as natural sources: one an active galactic nucleus, one a star-forming galaxy, both of whose elevated infrared emission could be explained within known astrophysical mechanisms.
The other two could not be explained.
Chen’s direct statement to Inverse magazine was about what the study found and what it did not find: the two remaining galaxies produced anomalous mid-infrared radiation whose cause could not be identified as natural. The study did not claim to have found alien civilizations. It claimed to have found something that natural processes do not account for in two galaxies, and concluded that both deserved further investigation.
The gap between what the study found and what would be required to explain it as the product of technological activity is the most important thing the piece has to say. What would a civilization have to be doing to produce a galaxy-scale mid-infrared anomaly visible across intergalactic distances?
Freeman Dyson’s Proposal
In 1960, physicist Freeman Dyson published a paper in Science whose brevity and specificity have made it one of the most consequential short papers in the history of the search for extraterrestrial intelligence.
Dyson’s argument was thermodynamic rather than speculative. He began from the observation that a technological civilization’s energy consumption grows over time, and that exponential growth in energy consumption eventually collides with the finite energy output of the civilization’s host star. A civilization that survives long enough will exhaust every terrestrial, oceanic, atmospheric, and orbital energy source before its star’s output becomes the binding constraint on further growth.
The solution Dyson proposed was engineering rather than discovery: surround the star with a shell or swarm of energy-capturing structures large enough to intercept most of the star’s total energy output. The form of the structure, whether a solid shell, a swarm of independently orbiting platforms, or some other configuration, he considered less important than the thermodynamic consequence: a star enclosed in such a structure would have its visible light output suppressed while re-radiating the civilization’s waste heat as infrared emission from the structure’s outer surface.
The temperature of the waste heat emission depends on the size of the enclosing structure. A Dyson Sphere at approximately the Earth-Sun distance would radiate at roughly 200-300 Kelvin, producing mid-infrared emission in the wavelength range of ten to twenty micrometers. This is exactly the wavelength range that the Chen-Garrett study examined.
Dyson’s prediction was direct and testable: a civilization that had surrounded enough stars with energy-capturing megastructures would produce a detectable mid-infrared excess in the galactic emission that the correlation between radio and infrared emission would not predict. The two anomalous galaxies in the Chen-Garrett study show exactly this characteristic.
The Kardashev Scale’s Thermodynamic Foundation
Nikolai Kardashev’s 1964 paper in the Soviet Astronomical Journal, published four years after Dyson’s, developed the framework that the source material summarizes but does not ground in its original physics.
Kardashev was addressing an engineering question in radio astronomy: what should the sensitivity and frequency characteristics of a SETI-optimized radio telescope be if we assume that extraterrestrial civilizations are transmitting at the maximum power levels their energy budgets permit? His answer required categorizing civilizations by their total energy budgets, which produced the Type I, II, and III classification.
The classification is not a scale of progress in the sense that higher is better. It is a thermodynamic scale of energy consumption, and its implications for detection are direct: a Type III civilization that uses galaxy-scale energy does not have the option of being thermodynamically invisible. The waste heat from energy use at that scale must be radiated somewhere in the electromagnetic spectrum, and the mid-infrared is where the thermodynamics places it.
Humanity is currently approximately Type 0.7 on the Kardashev Scale, consuming roughly ten to the thirteen watts of power from a combination of fossil fuels, nuclear, and renewable sources. A Type I civilization consumes approximately ten to the sixteen watts, the total solar energy incident on a planet. A Type II civilization consumes ten to the twenty-six watts, the total output of its star. A Type III civilization consumes ten to the thirty-six watts, the total output of its galaxy.
The difference between Type 0.7 and Type III is twenty-three orders of magnitude. It is not a difference in degree. It is a difference in kind so extreme that the concepts humanity uses to reason about technology, efficiency, capability, and resource management, become inadequate at the scale of a Type III civilization’s operations.
What the Chen-Garrett study is looking for is not evidence that a civilization comparable to ours exists elsewhere. It is evidence that a civilization so far beyond ours that the comparison is meaningless has left thermodynamic evidence of its operations in the galactic emission record.
The LOFAR Survey’s Methodology
The Low-Frequency Array is not a single instrument. It is approximately 100,000 individual antennas distributed across Europe, from Ireland to Latvia, linked by fiber-optic cable and processed by a central correlator in the Netherlands to function as a single telescope with an effective collecting area comparable to a dish kilometers across.
LOFAR observes in the 10-240 MHz frequency range, the low-frequency radio band where synchrotron radiation from cosmic ray electrons produces the characteristic emission of star-forming regions and active galactic nuclei. The sensitivity of LOFAR to this emission makes the radio-infrared correlation a robust diagnostic tool: in normal galaxies, the radio synchrotron emission from star formation correlates tightly with the infrared emission from dust heated by the same star-forming regions. The correlation is stable enough across galaxy types and distances that deviations from it are meaningful rather than random.
Chen and Garrett used this correlation as their anomaly detector. They selected 21 galaxies from the LOFAR survey with elevated average infrared emission, calculated the expected infrared emission for each galaxy based on its radio emission through the radio-infrared correlation, and identified galaxies where the actual mid-infrared emission significantly exceeded the prediction.
Four galaxies exceeded the prediction by a factor of ten. Two were explained. Two were not.
The methodology is published and the galaxies are named and catalogued. Independent researchers can access the LOFAR survey data and conduct their own analysis of the two anomalous sources. Whether the anomalies are confirmed by independent analysis, identified as natural sources through mechanisms the Chen-Garrett study did not consider, or remain unexplained through further investigation, is a question that the published methodology makes addressable through normal scientific processes.
Tabby’s Star and the Single-Star Precedent
Before the Chen-Garrett galaxy-scale search, the most extensively recorded anomalous infrared case in the SETI literature involved a single star in our own galaxy.
KIC 8462852, nicknamed Tabby’s Star after astronomer Tabetha Boyajian who led the team that characterized its unusual behavior, produced a light curve in the Kepler Space Telescope data that defied systematic explanation. The star’s brightness decreased irregularly and aperiodically by amounts ranging from one percent to twenty-two percent over periods of days to weeks, with no pattern consistent with any known natural process. Planetary transits produce regular, periodic, shallow dimming. Binary star occultations produce regular, predictable eclipses. Neither mechanism produced what Tabby’s Star was doing.
Jason Wright, an astronomer at Penn State who had developed predictions about what Dyson Swarm signatures would look like in stellar light curves, formally proposed the megastructure hypothesis in 2015. The proposal was covered extensively in the science press and generated significant observational follow-up from multiple telescopes across multiple wavelengths.
The subsequent analysis, including infrared observations that showed the star’s dimming events were wavelength-dependent in a way consistent with dust rather than a solid or metallic structure, provisionally shifted the scientific consensus toward a natural explanation involving circumstellar dust. Whether the dust explanation fully accounts for all of the star’s anomalous behavior is still debated in the astronomical literature.
What Tabby’s Star established, regardless of its eventual explanation, is that anomalous stellar dimming consistent with partial stellar enclosure can be detected in existing photometric data and that the Dyson megastructure hypothesis is a scientifically legitimate candidate explanation for anomalous stellar observations rather than a science fiction premise.
The Chen-Garrett study is the galaxy-scale extension of the search that Tabby’s Star made credible at the stellar scale. If partial stellar enclosure can produce detectable anomalies in a single star’s light curve, complete or near-complete stellar enclosure across thousands of stars in a galaxy can produce detectable anomalies in the galaxy’s integrated emission.
What Galaxy-Scale Means
The implication of the two anomalous galaxies being Type III civilization hosts deserves development beyond the Kardashev Scale summary.
A civilization that produces a detectable mid-infrared excess at the galaxy scale has not enclosed a few stars. It has enclosed enough stars to produce a thermodynamic signature visible across intergalactic distances with instruments comparable to LOFAR. The number of stars required depends on the fraction of stellar output being captured, but at any plausible efficiency, the number is in the thousands to millions.
Enclosing a thousand stars in Dyson Spheres requires manufacturing materials in quantities that exceed every resource on Earth by orders of magnitude. It requires engineering at a scale that the concepts humanity uses to think about large construction projects become meaningless. It requires a civilization with ten to the thirty-six watts of power available and the willingness to restructure the physical appearance of its home galaxy.
Such a civilization has been operating on a timescale that makes human civilization, from the first stone tools to the current moment, a brief flicker. It has solved every problem humanity currently faces, and problems humanity has not conceived of, and continued for long enough to restructure its galactic environment.
The two anomalous galaxies are not producing a subtle signal. They are producing an anomaly detectable with current instruments across intergalactic distances. Whatever is inside them that produces the anomalous emission has been operating long enough to be integrated into the galaxy’s emission profile at a level that changes the galaxy’s basic thermodynamic character.
If this is what it appears to be, the question it raises is not whether civilizations of this scale exist. It is what they are doing, what they have learned across the timescale their operations imply, and what their relationship to civilizations at our scale would be if such a relationship were possible.
The Fermi Paradox and the Infrared Answer
The Fermi Paradox, named for Enrico Fermi’s informal observation at Los Alamos in 1950, poses the question in its simplest form: given the age of the universe, the number of stars, and the apparent ease with which technological civilization develops once life exists, where is everyone?
The answers proposed over the subsequent seventy years include: civilizations are rare, civilizations destroy themselves, civilizations choose not to communicate, civilizations communicate in ways we cannot detect, and civilizations are not rare but their signals have not reached us yet.
The Chen-Garrett study provides an answer to the last possibility that does not require directed communication. A Type III civilization does not choose whether to be detectable. It cannot avoid being detectable. The waste heat from its energy use is an inescapable thermodynamic consequence. A civilization that has structured its galaxy around energy capture is announcing its existence in the mid-infrared whether it intends to or not.
The two anomalous galaxies may be that announcement. The announcement may have been traveling toward us for billions of years. We developed the instruments to detect it recently.
The Fermi Paradox asks where everyone is. The mid-infrared band may be where the answer has been waiting, at wavelengths our ancestors could not see and in galaxies our instruments could not resolve, for the entire duration of human civilization.
Chen’s paper concludes that the two galaxies deserve further study. The conclusion is appropriately cautious. What it is cautious about is one of the most significant possible implications of any astronomical observation in the history of the discipline.
The signal has already left. Two galaxies are producing it. The instruments that can read it are operational. The researchers who are looking are looking.
The answer to whether we are alone in the universe may be in the data that LOFAR has already collected, waiting for the analysis that determines whether what cannot be explained by natural processes can be explained by something else.
Something that enclosed thousands of stars. That has been operating for longer than complex life on Earth has existed. That we can see from here, now, if we know where to look and what to look for.
We are looking. We are not sure what we are seeing. That is where the most important investigations always begin.
