Constraints on the abundance of $0.01\,c$ stellar engines in the Milky Way

TL;DR

This paper investigates the maximum speeds achievable by hypothetical stellar engines, suggesting that speeds up to 0.1c are possible, and proposes using hypervelocity star surveys to constrain their abundance in the Milky Way.

Contribution

It provides theoretical limits on stellar engine speeds and explores how astrometric surveys can be used to detect or bound their prevalence.

Findings

Maximum stellar engine speeds could reach ~0.1c under optimal conditions

Natural astrophysical phenomena are unlikely to produce such high speeds

Hypervelocity star surveys can be used to search for or constrain stellar engines

Abstract

Stellar engines are hypothesized megastructures that extract energy from the host star, typically with the purpose of generating thrust and accelerating the stellar system. We explore the maximum potential speeds that could be realizable by stellar engines, and determine that speeds up to $\sim 0.1\,c$ might perhaps be attainable under optimal conditions. In contrast, natural astrophysical phenomena in the Milky Way are very unlikely to produce such speeds. Hence, astrometric surveys of hypervelocity stars may be utilized to conduct commensal searches for high-speed stellar engines in the Milky Way. It may be possible to derive bounds on their abundance, but this requires certain assumptions regarding the spatiotemporal distribution of such engines, which are not guaranteed to be valid.