A black hole usually hides its singularity behind an event horizon — an invisible boundary from which not even light can escape. But sometimes this 'cloak' is absent, and the singularity, a point where familiar physics breaks down, is exposed to an outside observer. Such objects are called naked singularities, and they cause theorists no end of trouble.

The authors of the new work took one of the most famous naked singularities — the Janis–Newman–Winicour (JNW) solution, generated by an ordinary scalar field (the simplest kind of matter, describable by a single number at each point). They applied a clever trick to its parameters: they rotated them into the complex plane using a so-called Wick rotation. The result was surprising: the singularity disappeared, and in its place emerged a traversable wormhole — a tunnel connecting two regions of flat spacetime. This is the famous Ellis class III wormhole, which was previously thought to be a completely different entity requiring exotic matter.

The discovery is far from accidental. The authors showed that the JNW solution belongs to a whole hierarchy of actions describing different theories of gravity. This means that 'fixing' one singularity automatically yields regular versions for an entire family of theories. So a single mathematical step untangles a knot of problems across different models.