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Microlensing Signatures of Dyson Sphere-like Structures around Primordial Black Holes as Technosignatures of Extraterrestrial Advanced Civilizations

This paper proposes a probabilistic framework for detecting extraterrestrial advanced civilizations by identifying anomalous, stochastic modulations in microlensing light curves caused by Dyson sphere-like structures surrounding primordial black holes, complemented by infrared excess signatures.

Original authors: Shant Baghram

Published 2026-02-17

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CC BY 4.0

Original authors: Shant Baghram

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you are looking up at the night sky, trying to find a needle in a haystack. But this isn't just any needle; it's a needle made of advanced alien technology, hidden inside a cosmic haystack of stars and black holes.

This paper, written by astrophysicist Shant Baghram, proposes a new, clever way to find that needle. Instead of listening for radio waves (like a cosmic phone call), the author suggests we look for cosmic shadows and glowing heat caused by giant alien megastructures.

Here is the breakdown of the idea, explained with simple analogies:

1. The "Needle": Primordial Black Holes (PBHs)

First, we need a target. The paper focuses on Primordial Black Holes. Think of these as tiny, invisible ghosts that formed right after the Big Bang. They are so small and dark that we usually can't see them.

How we find them normally: We use a trick called Gravitational Microlensing. Imagine holding a glass marble up to a streetlamp. The glass bends the light, making the lamp look brighter for a moment. Similarly, if a tiny black hole passes in front of a distant star, its gravity acts like that glass marble, briefly magnifying the star's light.
The problem: These events are rare and look exactly the same whether the black hole is empty or not.

2. The "Cosmic Solar Panel": The Dyson Swarm

Now, imagine an advanced alien civilization (like us, but much smarter) that needs a lot of energy. Instead of building a solid shell around a star (a classic "Dyson Sphere"), they build a Dyson Swarm.

The Analogy: Think of a Dyson Swarm not as a solid wall, but as a giant, chaotic cloud of solar panels orbiting a power source.
The Twist: The paper suggests these aliens might not be orbiting a normal star, but a Primordial Black Hole. They are harvesting energy from the black hole's accretion disk (the hot, swirling gas falling into it).
The Result: The black hole is surrounded by a cloud of debris and machines that are partially transparent (like a foggy window) and constantly moving.

3. The "Smoking Gun": How We Spot Them

If an alien swarm passes in front of a star, it changes the "flash" of light we see in two weird ways that a normal black hole wouldn't:

A. The "Flickering" Light Curve

Normal Black Hole: When a black hole passes a star, the light gets brighter and then dimmer in a smooth, predictable curve (like a gentle hill).
Alien Swarm: Because the swarm is made of many separate pieces (satellites, habitats, panels) with gaps between them, the light doesn't just get brighter; it flickers.
The Metaphor: Imagine looking at a lightbulb through a clear window (normal black hole). Now imagine looking at it through a swarm of bees flying in front of the window. The light would still get brighter overall, but it would jitter and flicker as individual bees block the light for split seconds.
The Paper's Finding: The authors created computer simulations showing that if we see a microlensing event that "jitters" or has random dips in brightness, it could be a sign of a Dyson Swarm.

B. The "Glowing Heat" (Infrared Excess)

The Concept: These alien machines aren't 100% efficient. They take energy from the black hole, use some of it, and dump the rest as waste heat.
The Metaphor: Think of a car engine. It burns fuel to move the car, but the engine gets hot. If you put a giant blanket of solar panels around a black hole, that "blanket" would get hot and glow.
The Signal: While the black hole itself is invisible, the alien swarm would glow brightly in infrared light (heat radiation). It's like seeing a campfire in the dark even if you can't see the wood. The paper calculates that telescopes like the James Webb Space Telescope (JWST) could spot this specific heat signature.

4. The Detective Work: What We Need to Do

The paper argues that we need to combine two clues to solve the mystery:

The Flicker: Look for stars that brighten due to a black hole but have a "jittery" light curve.
The Heat: Check if that same spot in the sky is glowing with extra infrared heat.

The authors ran the numbers and found that while it's rare, our upcoming telescopes (like the Vera Rubin Observatory and JWST) will be powerful enough to spot these events if they are happening. They estimate that if even a tiny fraction of black holes in our galaxy have these alien swarms around them, we might find one in the next few years.

Summary

This paper is a proposal to stop looking for aliens by listening to their radio, and start looking for their construction projects.

Old Way: Wait for a radio message.
New Way: Look for a black hole that is "wearing" a fuzzy, flickering coat of solar panels, glowing with waste heat.

It's like trying to find a secret base in a forest. You don't wait for someone to shout "Hello!"; instead, you look for a patch of trees that is moving strangely and giving off a weird amount of heat. If we see that, we might have found the first evidence of an advanced civilization.

1. Problem Statement

The search for Extraterrestrial Intelligence (SETI) has traditionally focused on detecting intentional signals (e.g., radio or laser transmissions). However, there is a growing interest in technosignatures: indirect indicators of advanced civilizations inferred from their engineering impact on the environment.

The Gap: While Dyson spheres (megastructures harvesting stellar energy) are a classic technosignature concept, their detection via direct imaging or infrared excess is challenging due to distance and confusion with natural astrophysical sources.
The Proposal: This paper proposes a novel detection strategy combining Primordial Black Holes (PBHs) as energy sources for advanced civilizations (Kardashev Type II+) and gravitational microlensing as the detection mechanism.
The Hypothesis: If an advanced civilization constructs a Dyson Swarm (a collection of orbiting structures) around a PBH to harvest energy from its accretion disk, the swarm will partially obscure the PBH. This would create unique, anomalous signatures in the microlensing light curve of background stars, distinct from standard point-mass lensing.

2. Methodology

The authors employ a multi-faceted theoretical and observational framework:

A. Physical Modeling of the Dyson Swarm around a PBH

Energy Source: Unlike traditional Dyson spheres around stars, this model utilizes the accretion disk of a PBH. The luminosity is derived from the Eddington luminosity ( $L_{Edd}$ ) scaled by an accretion efficiency factor ( $\eta$ ).
Thermodynamics: The authors model the Dyson structure as a "swarm" (stochastically varying, partially opaque) rather than a solid shell. They calculate the equilibrium temperature ( $T_{Dyson}$ $T_{D y so n}$ ) and radius ( $R_{Dyson}$ $R_{D y so n}$ ) based on energy balance, accounting for waste heat re-radiation.
- Equation (1) relates source luminosity, capture fraction, and waste heat temperature.
- Equation (6) derives the radius of the swarm around a PBH as a function of PBH mass, Eddington ratio, and temperature.
Parameters: The study assumes conservative values: Eddington ratio $\eta = 10^{-4}$ , energy transfer efficiency $\epsilon = 0.2$ , and various swarm temperatures (30 K to 3000 K).

B. Microlensing Simulation

Standard Baseline: The authors establish the standard Paczyński microlensing light curve for a point-mass lens (the PBH).
Anomaly Modeling: They introduce a stochastic transmission model to simulate the Dyson Swarm.
- The swarm is treated as having a specific optical depth ( $\tau_{Dyson}$ ) and area coverage.
- The model introduces "flickers" (random, short-duration dimming or brightening events) caused by the stochastic distribution of swarm components (satellites/habitats) passing in front of the lensed source.
- The ratio $\Xi_{D|PBH/E}$ (Dyson radius vs. Einstein radius) determines whether the swarm fully obscures the lens or creates partial/modulated effects.

C. Observational Strategy

Light Curve Analysis: Simulations of light curves for solar-mass PBHs at various distances ( $D_l = 4$ kpc, $D_s = 8$ kpc) with transverse velocities of 200 km/s.
Infrared Excess: Calculation of the thermal emission from the Dyson swarm to identify long-wavelength excesses (Wien's Law).
Statistical Framework:
- Calculation of Optical Depth ( $\tau$ ): The probability of a source being lensed.
- Calculation of Event Rate ( $\Gamma$ ): The frequency of detectable anomalous events per star per year.
- Signal-to-Noise Ratio (SNR) estimation for instruments like JWST and the Vera Rubin Observatory.

3. Key Contributions

Novel Technosignature Concept: Proposes the first theoretical framework for detecting Dyson Swarms specifically around Primordial Black Holes, expanding the search for technosignatures beyond host stars.
Stochastic Light Curve Model: Develops a probabilistic model for "flickering" microlensing events. Unlike standard smooth microlensing curves, a Dyson Swarm induces:
- Baseline Suppression: A reduction in peak magnification due to partial opacity ( $\tau_{Dyson}$ ).
- Stochastic Flickers: Random, short-duration dips or spikes in flux caused by the discrete nature of the swarm components.
Complementary Signatures: Identifies a dual-signature approach:
- Time-domain: Anomalous, flickering microlensing light curves.
- Spectral-domain: Infrared (IR) excess radiation from the waste heat of the swarm, peaking at wavelengths determined by the swarm's temperature.
Feasibility Analysis: Provides quantitative estimates for the optical depth and event rates, demonstrating that such events are within the detection capabilities of upcoming surveys.

4. Key Results

Light Curve Anomalies:
- Simulations (Figures 1–4) show that a Dyson Swarm with optical depth $\tau \approx 0.2$ to $0.5$ significantly dims the peak magnification of a standard microlensing event.
- The inclusion of "flickers" (simulated as 10–50 random events) creates a jagged, asymmetric light curve that deviates from the smooth Paczyński curve.
- The duration of these flickers ranges from $10^{-3}$ to $10^{-2}$ of the Einstein crossing time ( $t_E$ ).
Thermal Signatures:
- Table 1 and Figure 6 show that Dyson Swarms around PBHs emit peak radiation in the infrared.
- A swarm at $T \approx 300$ K peaks at $\sim 10$ $\mu$ m (within JWST/MIRI sensitivity), while hotter swarms ( $>1000$ K) peak in the near-IR (accessible to Roman/Euclid).
- The bolometric flux is linearly proportional to the PBH mass but independent of the swarm temperature (due to radius-temperature scaling cancellation).
Detection Probability:
- Using an NFW halo profile for the Milky Way, the authors calculate the optical depth for PBHs.
- Assuming a conservative fraction of PBHs hosting civilizations ( $f_{Dyson} = 0.01$ ) and a PBH dark matter fraction ( $f_{PBH} = 0.01$ ), the anomalous event rate is estimated at $\Gamma_{Dyson} \approx 10^{-9}$ stars $^{-1}$ year $^{-1}$ .
- For a survey monitoring $\sim 10^9$ stars (e.g., Vera Rubin or Roman), this implies a non-zero probability of detecting such an event within a year.
Instrumentation: The paper confirms that high-cadence monitoring (e.g., Vera Rubin) is required to resolve flickers, while space-based IR telescopes (JWST) are essential for detecting the thermal excess and confirming the nature of the source.

5. Significance

New Frontier in SETI: This work bridges Astrophysics, Cosmology, and SETI, proposing a method to detect civilizations that utilize compact objects (PBHs) rather than stars.
Robustness: The proposed signature (stochastic flickering + IR excess) is difficult to mimic by natural astrophysical phenomena (like variable stars or standard microlensing), making it a high-confidence technosignature.
Observational Readiness: The study demonstrates that current and near-future facilities (JWST, Vera Rubin, Roman) have the sensitivity and cadence to test this hypothesis.
Future Directions: The authors suggest using Bayesian inference for model selection, machine learning to classify modulated light curves, and analyzing chromatic/polarization signatures to further distinguish artificial swarms from natural sources.

In conclusion, the paper provides a rigorous theoretical foundation for searching for advanced civilizations by looking for "flickering" shadows cast by Dyson Swarms around Primordial Black Holes during gravitational microlensing events.