Intelligent civilizations across the universe, despite their differences, share one universal need: energy. On Nikolai Kardashev's scale, a Type III society could harness an entire galaxy's power—including its central supermassive black hole. By scanning for signs of this exploitation, astronomers might spot advanced extraterrestrial life, as such feats would leave detectable traces visible from Earth.
Advanced energy-harvesting tech could imprint a distinct signature just outside a spinning black hole's event horizon—the boundary where gravity traps light and matter forever. This might explain the plasma flares astrophysicists frequently observe near black holes.
Rotating black holes offer near-limitless energy for tech-savvy civilizations. Astrophysicist Luca Comisso from Columbia University stresses the key first step: modeling how artificial energy extraction from a black hole would appear to distant observers like us. This could enable detection of far-off alien societies.
The concept isn't new. In 1969, physicist Roger Penrose—who earned the 2020 Nobel Prize in Physics for black hole research—proposed the Penrose process. A particle splits near a black hole spinning near light speed; one part plunges into the ergosphere, a swirling spacetime region outside the event horizon, carrying negative energy. The escaping part gains energy extracted from the black hole.
Recent work by Comisso and colleagues scales this up to vast plasmas in the accretion disk—the scorching matter orbiting most black holes.
Plasmas pack countless particles, yielding massive energy yields. Black holes also slowly "evaporate" via Hawking radiation—a quantum effect theorized by Stephen Hawking—but it's far too faint to observe today.
Energy extraction likely stems from magnetic reconnection events outside the event horizon, where tangled field lines snap and reform. These power solar flares on stars like our Sun, hurling plasma in opposing jets.
Near a spinning black hole, one plasma jet enters the ergosphere, gaining negative energy, while its twin escapes with boosted energy drawn from the black hole. By pinpointing traits of engineered plasma capture, Earth-based scientists could identify technosignatures of alien energy harvesting.
