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.
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.