Can Hawking radiation cause black holes to evaporate?

Classically, black holes, once formed, are permanent. However, the discovery of Hawking radiation — an output of massless, chargeless bosons from black holes — calls this into question. If black holes are losing energy, and therefore mass, can they eventually evaporate to the point of nonexistence?

As time passes, this radiation settles into a constant stream. Fred Alford developed a mathematical proof of its limit, enabling a more quantitative treatment of black hole Hawking radiation.

“Many results studying how black holes evaporate assume that they are emitting exactly this thermal radiation, rather than approaching this thermal radiation,” Alford said. “While not exactly true, my result shows that this is a sensible assumption to make, as the error they are ignoring is tending to zero quickly enough to not be important.”

In general, the radiation emitted approaches a limit over time, Alford showed. However, for some black holes, the radiation emitted approaches zero.

“Though this has been known for a long time, I was — and am still — most surprised that the way the black hole formed does not impact the limit of the radiation emitted. This is often referred to as the information paradox,” said Alford. “While the way the black hole forms may affect exactly how the emitted radiation approaches its limit, it is surprising that this limit itself can’t be changed by making the black hole collapse faster or slower.”

Certain black holes, called extremal black holes, have as much charge as possible within their physical limits but a temperature of absolute zero. As a result, their radiation eventually comes to a stop, and understanding how quickly this happens provides a measure of the total radiation they emit throughout their lifetime — a finite value.

“This means that these black holes may not completely evaporate and so may just remain permanent fixtures of the universe,” Alford said.

Source: “A rigorous study of hawking radiation on collapsing charged spherically symmetric spacetimes,” by Fred Alford, Journal of Mathematical Physics (2026). The article can be accessed at https://doi.org/10.1063/5.0210032 .