"Once the black hole reaches the 20-microgram threshold, we find that it starts emitting purifying radiation [named because it is said to 'purify' the quantum state of the universe] due to behavior that is characteristic of a white hole.

"Therefore, even though we do not yet know the physics near a white hole, we identify an object that has exactly the same properties from far away."

White holes are another hypothetical entity in physics, suggested to be effectively a "time-reversed black hole" that, rather than trap matter and radiation within them as black holes do, endlessly push matter and radiation away.
Any further predictions about the fate of these primordial black holes taking on a white hole appearance would require a theory that unites general relativity and quantum mechanics, known as "quantum gravity," that has steadfastly evaded physicists since the early 20th century.
"Simple physical assumptions about the physics far away from a black hole can tell us a lot about their lifetime and about their transition to a stable phase that looks like a 20 microgram white hole," Paraizo said. "The fact that we can infer these properties, using only minimal ingredients from quantum gravity, is remarkable."

Robert Lea

https://www.space.com/astronomy/black-holes/can-black-holes-turn-into-white-holes-its-not-such-a-crazy-idea-scientists-say