What remains after a black hole evaporates to the Planck scale?
In plain words
Hawking's calculation stops working when the black hole shrinks to about $2 x 10^{-5}\,\mathrm{g}$, the Planck mass. The options include complete disappearance into radiation, a stable tiny leftover, a white hole, or a disconnected baby universe.
Precise statement
For a Schwarzschild black hole evaporating from $M \gg m_P=\sqrt{\hbar c/G}$, approximately $2.2 x 10^{-5}\,\mathrm{g}$, determine the final state at $M \sim m_P$: complete evaporation with a pure final radiation state, a stable or long-lived remnant, a black-to-white-hole transition, or topology change. An answer is a classification derived in a UV-complete or otherwise controlled framework, giving the remnant mass and lifetime if any and the entropy carried by the final burst.
What would settle it
A controlled quantum gravity calculation of the last stage of evaporation, or an observation of the final burst of a primordial black hole.
Related problems
- More general than Does an evaporating black hole tunnel into a white hole?
- More general than Are long-lived Planck-mass remnants consistent with quantum field theory?