On the Possibility of Detecting Class A Stellar Engines Using Exoplanet Transit Curves

Abstract: The Class A stellar engine (also known as a Shkadov thruster) is a spherical arc mirror, designed to use the impulse from a star's radiation pressure to generate a thrust force, perturbing the star's motion. If this mirror obstructs part of the stellar disc during the transit of an exoplanet, then this may be detected by studying the shape of the transit light curve, presenting another potential means by which the action of extraterrestrial intelligence (ETI) can be discerned. We model the light curves produced by exoplanets transiting a star which possesses a Shkadov thruster, and show how the parameters of the planet and the properties of the thruster can be disentangled. provided that radial velocity follow-up measurements are possible, and that other obscuring phenomena typical to exoplanet transit curves (such as the presence of starspots or intrinsic stellar noise) do not dominate. These difficulties aside, we estimate the a priori probability of detecting a Shkadov thruster during an exoplanet transit, which even given optimistic assumptions remains stubbornly low. Despite this, many exoplanet transit surveys designed for radial velocity follow-up are on the horizon, so we argue that this remains a useful serendipitous SETI technique. At worst, this technique will place an upper limit on the number of Class A stellar engines in the Solar neighbourhood; at best, this could help identify unusual transiting exoplanet systems as candidates for further investigation with other SETI methods.

• The paper proposes detecting hypothetical Class A stellar engines by analyzing anomalies they might cause in exoplanet transit light curves.
• It concludes that the prior probability of detection is low due to factors like structure orientation and confusion with natural astrophysical noise like starspots.
• The work contributes to Dysonian SETI by suggesting that ongoing exoplanet surveys could potentially provide data for serendipitous detection of such macro-engineering.

Overview of Detecting Class A Stellar Engines Using Exoplanet Transits

The paper "On the Possibility of Detecting Class A Stellar Engines Using Exoplanet Transits" by Duncan H. Forgan explores a novel method for detecting megastructures, specifically Class A stellar engines (or Shkadov thrusters), using the transit method common in exoplanet studies. The work integrates principles from the Search for Extraterrestrial Intelligence (SETI) with astrophysical observations, proposing an indirect approach to identify signatures of extraterrestrial technological activities.

Summary

Class A stellar engines, also known as Shkadov thrusters, are hypothetical megastructures that could theoretically manipulate star motion by generating thrust through the reflection of stellar radiation. The paper suggests that if such a structure were to partially block a star's light during an exoplanetary transit, it might produce a distinctive anomaly in the transit light curve. The author models these potential anomalies, examining how parameters of the transit could be disentangled to detect the presence of such a structure.

The paper is structured to discuss the physics of Shkadov thrusters, reviewing the standard shape of transit curves and how they are modified in the presence of a Shkadov thruster. The author provides a methodology to deconstruct transit signals to retrieve parameters of both the transiting planet and the stellar engine. However, the likelihood of detecting a Shkadov thruster in current and future exoplanet surveys remains low due to several factors, including the orientation of the structure and intrinsic astrophysical noise.

Key Results and Claims

• Low Probability of Detection: Even with optimistic assumptions, the paper estimates a low prior probability for detecting Shkadov thrusters during exoplanet transits. Calculations rely on current estimates of intelligent civilization occurrences, such as SETI's Drake Equation, to assert this probability.
• Potential Confusion with Natural Phenomena: The difficulty in distinguishing Shkadov signals from natural astrophysical noise, such as starspots or intrinsic stellar variations, is highlighted.
• Parameter Degeneracies: The degeneracy between stellar and planetary parameters in the presence of a stellar engine is explored, suggesting that combined transit and radial velocity measurements are essential for disentangling these elements.

Implications

The paper contributes to the Dysonian SETI approach, which suggests looking for large-scale astroengineering efforts instead of relying solely on intentional signals. Should a Shkadov thruster be detected, it would signify an advanced civilization exercising stellar-scale engineering capabilities.

Practically, the research implies that while the probability of detecting such structures is low, ongoing and future exoplanet surveys could provide valuable datasets for serendipitous detection. The inclusion of such megastructure search strategies in broader SETI initiatives could provide constraints on the prevalence of advanced civilizations.

Future Directions

Future developments in astronomical instrumentation and methodologies could aid in refining this search strategy. Increased focus on high-cadence photometric surveys coupled with precise radial velocity measurements may enhance the detection capabilities for such signatures. Further exploration into the integration of interferometric and asteroseismic techniques could strengthen the ability to confirm suspected detections.

Considering the potential for technological advancements in both observing facilities like TESS and CHEOPS and analytical methods, SETI strategies may expand to incorporate broader techniques to discover noomarkers or technomarkers indicative of advanced extraterrestrial civilizations.

In conclusion, the paper presents a detailed theoretical exploration of detecting Shkadov thrusters via exoplanet transit curves, advocating for its utility as part of a diversified SETI toolkit. The research remains a speculative but scientifically grounded approach to identifying signs of extraterrestrial macro-engineering.