Long-lived black holes: how their slow boiling is heard in a radio signal from the past ⚡ экспресс
Primordial black holes are candidates for dark matter. If the quantum 'memory burden' effect slows their evaporation, then lightweight holes (with masses up to 10^15 g) survive until the cosmic dawn and heat up hydrogen gas. This changes the global 21 cm radio signal we detect today. Calculations show that holes in the 10^8–10^13 g range are ruled out if their fraction of dark matter exceeds 10^-8. Interestingly, when the memory effect switches on rapidly, the constraints disappear—nature seems to be covering its tracks.
Tiny black holes, born in the first moments after the Big Bang, should have disappeared long ago according to Hawking's theory — evaporated like a puddle of water under the sun. But new calculations show evaporation isn't that fast. The hole seems to choke on its own radiation — like a boiling pot covered by a cloud of steam, slowing the boil. This 'memory burden' effect turns an instantaneous flash into a long, slow fading.
Such 'underboiled' holes spent eons warming the surrounding hydrogen in the young universe. Hydrogen atoms, feeling the heat, change their radio voice — 21-cm radiation. Astronomers catch this ancient signal and see it's too cold. If black holes were more than a tiny fraction, they would have heated the gas more, distorting the radio picture. So these objects cannot be dark matter — their number is less than one ten-millionth of the required amount.
🎯 The most sensitive tool for hunting dark matter isn't a giant underground detector, but an ordinary radio telescope listening to the echo of hydrogen from the time before the first stars lit up.