Energy Rate Density as a Technosignature : The Case for Stellivores

The energy rate density (ERD) metric is the central scientific measure underlying all of big history. It measures the rate at which free energy transits in a complex system of a given mass. How could it inform SETI and astrobiology? One simple way to proceed is to look for high ERD systems in the universe and binary systems in accretion are excellent candidates. I argue that these accreting binary systems might be instances of Type II stellar civilizations on Kardashev’s scale, civilizations feeding on stars, or stellivores. I review living clues, such as their sheer variety, their existence far from thermodynamic equilibrium, the fine-tuning of their models, the existence of reserves, accretion and ejection control. I summarize these clues using living systems theory. I use known binary stars masses and accretion rates to compute the ERD of putative stellivores, such as cataclysmic variables (130), neutron stars (30) and transient black holes (19). The results support an anomalously high ERD. I discuss objections and counterarguments regarding the stellivore hypothesis, and implications for big history.