What happens if black holes fall into wormholes? A new way to find out.
Astronomers believe they may be able to detect black holes collapsing into wormholes using ripples in spacetime known as gravity waves, but only if wormholes exist and such a scenario has ever occurred, according to a study.
Gravity is affected by the way mass warps space and time, according to Einstein, who predicted the existence of gravitational waves in 1916. When two or more objects move within a gravitational field, gravitational waves are produced that travel at the speed of light, stretching and squeezing space-time in the operation.
Gravitational waves are incredibly difficult to detect since they are extremely weak, and even Einstein was doubtful whether they existed and would be discovered. After decades of work, scientists reported the first direct evidence of gravitational waves in 2016, detected using the Laser Interferometer Gravitational-Wave Observatory (LIGO).
Black holes vs. wormholes
More than 20 huge collisions involving incredibly dense and massive objects like black holes and neutron stars have been discovered by gravitational-wave observatories. However, more exotic objects may theoretically exist, such as wormholes, the collisions of which should also produce gravitational signals that scientists could detect.
Wormholes are spacetime tunnels that, in principle, can transport you anywhere in space and time, or even to another universe. Einstein’s theory of general relativity allows for the possibility of wormholes, although whether they really exist is another matter.
In theory, all wormholes are unstable, closing as soon as they open. The only way to keep them open and accessible is to use an unusual type of substance with “negative mass.” Exotic matter has strange properties, such as flying away from a typical gravitational field rather than falling toward it as normal matter does. Nobody knows if such an exotic substance exists.
A wormhole is similar to a black hole in many ways. Both types of objects are extremely dense and have strong gravitational pulls for their size. The primary difference is that no item may theoretically escape a black hole’s event horizon — the point at which the speed required to escape the black hole’s gravitational pull exceeds the speed of light — whereas any object entering a wormhole can theoretically reverse course.
Scientists explored the gravitational signals generated when a black hole orbits a wormhole for a paper, which has not yet been peer-reviewed. The researchers also investigated what might happen if a black hole enters one mouth of a wormhole, exits out the other mouth into another point in space-time, and then falls back into the wormhole and emerges on the other side, assuming the black hole and wormhole are gravitationally bound to one another.
The researchers used computer models to investigate the interactions of a black hole five times the mass of the sun and a stable traversable wormhole 200 times the mass of the sun with a throat 60 times wider than the black hole. The models predicted that when the black hole traveled into and out of the wormhole, it would produce gravitational signals unlike anything already seen.
When two black holes spiral closer together, their orbital speeds rise, similar to how spinning figure skaters bring their arms closer to their bodies. As a result, the frequency of gravitational waves increases. These gravitational waves would produce a chirp, similar to rapidly increasing the pitch on a slide whistle, because any increase in frequency corresponds to an increase in pitch.
If one watched a black hole spiral into a wormhole, one would see a chirp much like two black holes meeting, but the gravitational signal from the black hole would quickly fade as it radiated most of its gravitational waves on the other side of the wormhole. (When two black holes meet, the outcome is a massive blast of gravitational waves.)
When a black hole emerges from a wormhole, it emits a “anti-chirp.” The frequency of gravitational waves produced by the black hole would decrease as it traveled away from the wormhole.
As the black hole keeps journeying in and out of each mouth of the wormhole, it would generate a cycle of chirps and anti-chirps. The period between each chirp and anti-chirp would shrink with time until the black hole became stuck in the wormhole’s throat. The detection of this type of gravitational signal may give evidence of the existence of wormholes.
“Though wormholes are very, very speculative, the fact that we might have the ability to prove or at least give credibility to their existence is pretty cool,” study co-author William Gabella, a physicist at Vanderbilt University in Nashville, told Space.com.
In this scenario, the black hole would finally stop falling in and out of the wormhole and would settle near its throat. The consequences of such a conclusion are entirely dependent on the totally hypothetical qualities of the exotic materials discovered in the wormhole’s throat. One scenario is that the black hole has effectively increased the wormhole’s mass, and the wormhole does not contain enough exotic matter to remain stable. According to Gabella, the resulting disruption in space-time may cause the black hole to convert its mass to energy in the form of an unusual number of gravitational waves.
A wormhole should be stable as long as it has a bigger mass than any black hole it encounters. If a wormhole collides with a larger black hole, the black hole may disrupt the wormhole’s exotic matter sufficiently to destabilize it, leading to its collapse and likely generating a new black hole, according to Gabella.
It is unclear what would happen if a black hole just clipped the edges of a wormhole, with a part of the black hole entering the wormhole’s mouth and the rest staying outside it. “I suspect that there would be some crazy behavior at the black hole event horizon giving rise to even more gravitational waves and more energy loss,” Gabella said. Such a collision may also disrupt the wormhole’s exotic matter, “leading to an unstable wormhole,” he added.
Future studies can investigate the interactions between exotic matter in a wormhole and any normal matter entering the wormhole, as well as more complex scenarios, such as what might happen if the wormhole is spinning, according to Gabella. Other study avenues might look at how gravitational waves interact with both ordinary and exotic matter in these settings, as well as “the variety of orbits that might arise between wormholes and you name it,” he added.
The researchers published their findings online in the journal Physical Review Letters. The findings were published on the preprint site arXiv.org.