Simulating binary Ellis-Bronnikov wormholes in three dimensions reveals that their collisions can form a black hole with a shrinking horizon, according to a preprint published on arXiv by Nikita M. Shirokov of the Moscow Institute of Physics and Technology and Ilya Nachevsky of the Higher School of Economics in Russia.
Simulating Binary Ellis-Bronnikov Wormhole Collisions
To determine what cosmic fireworks might occur when wormholes cross paths, Shirokov and Nachevsky ran three-dimensional simulations of pairs of Ellis-Bronnikov wormholes. They varied the initial separation of the objects, their trajectories, and the properties of the phantom scalar fields holding the throats open. The wormholes featured in the study are traversable passages sustained by a hypothetical phantom scalar field with unusual negative-energy properties that prevent the throat from pinching shut. Even a small disturbance can upset this delicate balance, causing the throat to collapse into a black hole or begin a runaway expansion known as inflation.
The simulations produced surprisingly diverse outcomes depending on the chosen configuration. Some wormholes attracted each other while others repelled. Certain pairs passed close enough to interact before flying apart, with their throats expanding dramatically during the encounter. Other wormholes plunged straight toward each other. Instead of merging into a single larger wormhole, a common apparent horizon formed around both throats, enclosing them inside a developing black hole.
Shrinking Apparent Horizons and Gravitational Wave Signatures
As the phantom scalar field fell into the collapsing region of space, the newly formed apparent horizon shrank, losing about 28 percent of its area. Stephen Hawking formulated his black hole area theorem in 1971, which dictates that under typical conditions, the boundary surface of a black hole’s event horizon will either expand or remain constant. However, that theorem relies on energy behavior assumptions that the phantom scalar field violates, allowing the simulated horizon to decrease in size.
When heavy bodies like black holes orbit closer together toward a crash, they create a unique waveform known as a chirp that steadily intensifies and rises in pitch as the pair converges. By contrast, the wormhole encounters modeled in the study produced short, sharp bursts of gravitational waves. The precise shape and strength of these signals depended on whether the wormholes plunged directly into each other or merely grazed each other in passing. Closely spaced flybys produced particularly strong gravitational-wave bursts even without forming a common apparent horizon.
Detecting Exotic Spacetime Physics in the Cosmos
Generating a gravitational-wave burst without a chirp is not evidence of wormholes, as black holes can also produce such signals under certain circumstances. One unusual signal designated GW190521, detected in 2019, has been investigated as a possible signature of exotic spacetime physics. The new simulations do not establish a connection to that event. Furthermore, wormholes formed in the early Universe would produce signals stretched by cosmic expansion to frequencies far below the detection limits of observatories such as LIGO and the planned LISA mission. For these signals to be detectable, the wormholes would need to form much later in cosmic history, and scientists do not currently know how that could happen.
Frequently Asked Questions
What holds an Ellis-Bronnikov wormhole open?
An Ellis-Bronnikov wormhole is a traversable passage sustained by a hypothetical phantom scalar field possessing unusual negative-energy properties that prevent the throat from pinching shut.
How does the simulated wormhole collision defy Stephen Hawking’s theorem?
When two simulated wormholes formed a common apparent horizon, the horizon lost about 28 percent of its area as the phantom scalar field fell into the collapsing region of space. This does not contradict the 1971 black hole area theorem, as the simulation involves an apparent horizon and a field that violates the theorem’s assumptions.
Why can current observatories like LIGO not easily detect wormhole collisions?
Wormholes formed in the early Universe would produce gravitational wave signals that have been stretched by cosmic expansion to frequencies far below the operational range of observatories such as LIGO and the planned LISA mission.
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