Measuring Black Holes with Spacecraft Stopwatches express
A pebble dropped in a pond creates curved ripples, but from far away they appear as straight lines. Gamma-ray flashes from an evaporating black hole behave the same: a distant burst sends flat waves, while a nearby one arrives curved.
Astronomers use this curvature to measure distance. By comparing the tiny time lags between satellites (because the speed of light is constant), they can pinpoint the source. This technique, using light measurement (photometry), has been checked with NASA's Swift satellite. No curved signals appeared within 1.2 AU — the Earth-Sun gap. But future deep-space probes could search farther. The prey are primordial black holes: relics from the Big Bang, smaller than an atom yet heavier than a skyscraper. If one evaporates, it would emit a Hawking radiation burst we could catch.
Original abstract
as written by the authors arXiv:2603.16508
A nearby primordial-black-hole (PBH) evaporation burst would produce a curved gamma-ray wavefront, leading to detectable departures from plane-wave inter-satellite delays. We introduce a purely geometric method that combines imaging localizations with multi-spacecraft timing to determine the distance of a gamma-ray transient. Applied to \textit{Swift}-localized short GRBs, the current sample shows no significant deviation from the plane-wave expectation, with the most constraining event reaching $$1.2$$ AU and already probing a meaningful Solar-System-scale regime. Our analysis shows that direct distance measurements are achievable to $$10^3$$ AU scales with the current and near-future technical capabilities. Once a finite source distance is measured, the corresponding PBH mass and lifetime can be directly inferred. Future wide-field localization and long-baseline deep-space gamma-ray detectors could extend such searches to $$10^5$$ AU and beyond.
Primordial black holes, if they exist, are tiny but incredibly dense — remnants from the Big Bang — and they could be evaporating today, flashing gamma rays detectable by deep-space probes.