From the laws of energy conservation and the requirement of quantum state purification in asymptotically semiclassical spacetimes, constraints on the lifetime of an evaporating black hole are derived. Using the expression for the Bondi flux of Hawking radiation and entanglement entropy at future null infinity, the purification phase after the last semiclassical ray is examined. A lower bound on the purification time is found: T ~ M0⁴/ħ³/² (M0 is the initial mass). The assumption of a metastable Planck-mass black hole leads to an exponential dependence of time on the square of the initial mass (initial area). A negative redshift parameter points to a white-hole remnant that slowly releases information. The phenomenology of primordial black holes is discussed.
Black holes are not eternal: they slowly lose energy, emitting entropy — a measure of hidden information — as heat. This process was predicted by Stephen Hawking. But until now, it remained a mystery what happens at the very end, when the hole has almost disappeared and must return the captured data.
Now physicists have shown: after the main mass evaporates, a tiny white hole remains. Like a dying ember, it slowly releases information. The time for this 'cleanup' grows with the mass of the original black hole far more steeply than previously thought.
Perhaps we will be able to see the faint radiation from these remnants — maybe they are hiding under the mask of dark matter.
🎯 The complete evaporation time for a black hole with the mass of a mountain exceeds the age of the Universe by billions of times. And microscopic holes from the dawn of time may be burning out right now, and their last heat could be detected.