Black holes evaporate slowly, and toward the end of this process, they may begin to behave like white holes—repelling matter instead of attracting it. This is the conclusion reached by a group of physicists who refined the formula for the minimum lifetime of a black hole.
What’s wrong with the old formula?
As early as 1974, Stephen Hawking demonstrated that black holes are not eternal. Quantum particles can “seep” through the event horizon, and the black hole gradually loses mass—due to what is known as Hawking radiation. The smaller the mass, the more intense the radiation, and eventually the black hole disappears completely.
Hawking calculated the duration of this process, but his formula only worked under certain conditions: he assumed that quantum effects were small enough not to impact the structure of spacetime. This is acceptable for ordinary black holes. For primordial black holes—which are hypothesized to be very light—it is not.
New lower bound
The authors of a new paper published on arXiv in 2026 approached the problem differently. They made one key assumption: no matter how strangely spacetime behaves near the event horizon, at large distances it still reverts to classical behavior. Under this condition, they were able to obtain a lower bound on the lifetime of a black hole with a given mass.
The actual duration could be longer—it depends on how science ultimately resolves the information paradox, that is, the question of whether information about matter disappears along with a black hole. But it won’t be any shorter.
Three phases and a metastable state
The researchers also described three successive phases of evaporation. Initially, the black hole emits radiation via the Hawking mechanism—that is, slowly and predictably. This is followed by a transitional phase. After that comes the phase of quantum entanglement, which cannot be calculated without a fully developed theory of quantum gravity.
This is where the most interesting effect comes into play: a black hole can enter a metastable state—a sort of limbo between existence and disappearance—where, instead of absorbing matter, it begins to push it outward. From the outside, this would look like a white hole.
Can they be found?
Primordial black holes formed in the first fractions of a second after the Big Bang. At that time, matter was distributed unevenly, and in the densest regions it collapsed under its own gravity, even before the first stars appeared.
They do not emit light, but they have mass, which is why they are considered a possible explanation for dark matter—an invisible substance that accounts for most of the mass of the Universe, but whose nature has not yet been confirmed.
According to Universe Today
