Wormhole collision simulation produces strange gravitational waves

Russian physicists have used computer simulations to study what happens when two wormholes of a special type collide. According to their findings, such events could produce short, sharp bursts of gravitational waves that differ markedly from the signals of merging black holes.

Gravitational waves and wormholes

Gravitational waves have become a familiar tool for astronomers: scientists have recorded hundreds of such signals, and most of them come from black hole collisions. But many discoveries still lie ahead. Do similar waves arise when wormholes collide, and how would we recognize such a signal if we managed to catch one?

The question was tackled by physicist Nikita Shirokov of the Moscow Institute of Physics and Technology and machine learning specialist Ilya Nachevsky of the Higher School of Economics. They described scenarios in which pairs of Ellis–Bronnikov wormholes interact. By their estimate, most of the scenarios turned out to be strange, to say the least.

Wormholes sound like science fiction, but they follow from Einstein's general theory of relativity. They are a kind of tunnel, a shortcut between two, possibly very distant, points in space. Whether they actually exist in our Universe is still unknown, but that does not stop theorists from experimenting with them.

A tunnel that does not close

The best-known model is the Einstein–Rosen bridge. Ironically, it is a wormhole that leads nowhere. There are other models, such as Ellis–Bronnikov wormholes. Their tunnel is supposed to stay traversable thanks to a phantom scalar field. This field is entirely hypothetical: it has negative energy, and it is precisely this energy that keeps the wormhole from collapsing.

Such wormholes can hardly be called stable: even a small disturbance can knock them out of equilibrium. They can collapse into a black hole or trigger inflation and expand uncontrollably.

What the simulations showed

The researchers simulated the meeting of two such wormholes, and the results turned out remarkably varied. The wormholes could attract or repel each other. Some came close enough to interact and then moved apart again. Around the throats of others, a common apparent horizon formed, similar to the event horizon of a black hole. Stranger still, because of the exotic properties of the phantom field, this horizon began to shrink.

The main observation: the gravitational waves from such collisions differ markedly from the signals produced when two black holes spiral toward each other. They are short, sharp flashes, a sort of gravitational bark. Gravitational-wave astronomers now have a new hint about what to look for in the ocean of gravitational waves.

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Around Prague, based on reporting by osel.cz