There is a problem with black holes—they present an edge, called an event horizon, from which nothing can escape. This is in conflict with quantum mechanics, whose postulates ensure that information is always preserved, not lost.
One of the theoretical ways to deal with this conflict is to explore the possibility that the alleged black holes we ‘observe’ in nature are no such thing, but rather some type of exotic compact objects (ECOs), such as wormholes, which do not have an event horizon.
Researchers discuss wormhole collisions in a Phys. Rev. D paper called Echoes of Kerr-like wormholes.
The team of the KU Leuven University, in which Professor Thomas Hertog also participated, has presented a model that predicts how gravitational waves caused by the collision of two rotating wormholes would be detected.
The gravitational wave signals observed so far are completely extinguished after a few moments as a consequence of the presence of the event horizon. But if this did not exist, these oscillations would not disappear altogether; rather, after some time, there would be echoes in the signal, which may have gone unnoticed until now due to a lack of models or theoretical references with which to compare.
“Wormholes do not have an event horizon, but act as a space-time shortcut that can be traversed, a kind of very long throat that takes us to another universe,” Bueno explains, “and the fact that they also have rotation changes the gravitational waves they produce.”
Structure at the horizon scale of black holes would give rise to echoes of the gravitational wave signal associated with the postmerger ringdown phase in binary coalescences. Researchers study the waveform of echoes in static and stationary, traversable wormholes in which perturbations are governed by a symmetric effective potential. They argue that echoes are dominated by the wormhole quasinormal frequency nearest to the fundamental black hole frequency that controls the primary signal. They put forward an accurate method to construct the echoes’ waveform(s) from the primary signal and the quasinormal frequencies of the wormhole, which we characterize. They illustrate this in the static Damour-Solodukhin wormhole and in a new, rotating generalization that approximates a Kerr black hole outside the throat. Rotation gives rise to a potential with an intermediate plateau region that breaks the degeneracy of the quasinormal frequencies. Rotation also leads to late-time instabilities that, however, fade away for small angular momentum.