Wormhole Shadow: Sharp Angles When Rotating express
A wormhole is a tunnel through space, connecting distant regions of the Universe. Its shadow against a bright gas background was long thought to be as round as that of a black hole. But for a rotating wormhole (one you could actually traverse), the shape of the shadow might be surprising: the edge becomes jagged, like a gear.
If light passing through its throat is strongly 'stretched' (shifting in color toward red), then rotation causes the shadow to develop sharp protrusions. Researchers found a critical threshold: as soon as this stretching reaches a certain value, the shadow abruptly acquires teeth.
Such a 'jagged' silhouette is a key for future telescopes. If instead of a smooth shadow astronomers see a structure with notches, it would point not to a black hole, but to a wormhole.
Original abstract
as written by the authors arXiv:2602.14182
We investigate the shadow cast by a rotating traversable wormhole in the Teo class endowed with a general redshift function, with particular emphasis on the emergence of cuspy structures. The shadow boundary is the common envelope of two critical orbit families: unstable circular orbits outside the throat and orbits at the throat itself. The formation of cusps, marking the transition between smooth and cuspy shadow boundaries, only becomes possible when the redshift parameter $$\lambda$$ is allowed to vary. Moreover, we uncover a universal critical value $$\lambda_c$$ that signals the onset of the cusp. A phase diagram characterized by the spin and redshift parameters reveals four distinct morphologies: smooth, cuspy, ears touching, and throat drowning. The morphology of the wormhole shadow may provide observational diagnostics for the different compact objects in future high-resolution imaging observations.
Wormholes haven't been discovered yet, but Einstein's equations allow for their existence — just like black holes once were.
In Interstellar, the journey through a wormhole happened without its shadow — too bad: perhaps it would have looked like a gear.