Researchers from the University of Valencia and the University of Lisbon have looked beyond general relativity in an attempt to solve the main problem with black holes: the infinite singularity at their center.

The black hole they looked at is a special case that doesn’t exist in nature, as it’s electrically charged and doesn’t rotate on itself. In their solution, the singularity is not a point of infinite density but a wormhole, a bridge towards a different location in time and space.

To reach this solution, published in Classical and Quantum Gravity, the scientists liken the black hole to a graphene layer or a crystal. Their geometry can be used to reproduce the geometry of space-time within black holes all the way to the singularity.

“Just as crystals have imperfections in their microscopic structure, the central region of a black hole can be interpreted as an anomaly in space-time, which requires new geometric elements in order to be able to describe them more precisely,"  said lead author Gonzalo Olmo, from the University of Valencia, in a statement. "We explored all possible options, taking inspiration from facts observed in nature."

Describing the singularity of a black hole has so far proven incredibly complicated, and to provide a full description of it, it’s necessary to combine relativity and quantum mechanics – but they don’t play well together. 

“Our theory naturally resolves several problems in the interpretation of electrically-charged black holes," Olmo explained. “In the first instance, we resolve the problem of the singularity since there is a door at the center of the black hole, the wormhole, through which space and time can continue.”

In their interpretation, the singularity is replaced by a wormhole whose size is directly proportional to the electrical charge of the black hole. The bigger the charge, the bigger the wormhole. Theoretically, a brave explorer could jump into this black hole, where he or she would then be stretched by the intense tidal forces (in a process called spaghettification), pass through the wormhole, and return back into the universe in a single piece.

This discovery is curious because although wormholes are predicted in general relativity, they usually require some exotic matter to be stable. These wormholes instead appear simply from ordinary matter and energy.

Electrically charged black holes are not believed to form in nature, but it’s important to investigate their properties, especially if they lead to peculiar solutions like a stable wormhole. After all, even real black holes were once considered just a quirky theoretical idea.