The known universe is full with intriguing phenomena such as black holes, hypernovas, and merging neutron stars. All of them, however, appear benign in comparison to objects that physicists believe exist but have yet to discover. Wormholes, which potentially connect sections of space and time and allow anyone who enter them to travel to faraway regions, are perhaps the most notable of these.
The potential of wormholes came as a big relief to science fiction authors, who were previously blocked off from the star systems they wanted to explore due to physical restrictions prohibiting faster-than-light transit. Many scientists doubt they exist, or that three-dimensional things could travel through them unharmed, yet the sheer possibility enticed authors to send a starship, or at least a novel, through.
As telescopes progress, a more serious issue arises: if wormholes exist, why haven’t we discovered any? Four Bulgarian scientists provided a response in Physical Review D: perhaps we have and just haven’t acknowledged it.
The vast majority of black holes have been found based on their gravitational effects on nearby stars or the jets of material that blast out of their accretion disks. We’d probably never know whether any of these were wormholes. However, the Event Horizon Telescope Collaboration’s detection of the polarization near M87* and subsequent follow-up on Sagittarius A* is a different story. In these circumstances, we observed the shadow of the item itself against its event horizon, and we may expect to see anything if we were really looking at a wormhole.
The prospect of wormholes fascinates physicists, as evidenced by the 12 publications released to ArXiv.org since the beginning of November. However, as Petya Nedkova of the University of Sofia and co-authors point out, we do not know what they might look like.
The research attempts to answer this and finds that, when viewed from a high angle, wormholes appear to be nothing we’ve seen before. For minor inclination angles, the authors believe a wormhole would have “a very similar polarization pattern” to a black hole. As a result, M87*, observed at an estimated angle of 17°, may be a wormhole and we wouldn’t know.
That is not to argue that we will always be unable to distinguish between wormholes and black holes. “More significant distinctions are observed for the strongly lensed indirect images, where the polarization intensity in the wormhole spacetimes can grow up to an order of magnitude compared to the Schwarzschild black hole,” the study’s authors wrote. The lensing described here is not caused by a big object between us and the hole, which creates a gravitational lens. Instead, it is due to photons’ routes being warped by the hole’s tremendous gravitational field, forcing them to make a half circle around it before going toward us.
The scenario becomes more convoluted if we believe, as the authors do, that material or light may go in either direction through a wormhole. If this is true, scientists anticipate that “signals from the region beyond the throat are able to reach our universe.” These will alter the polarized picture of the disk we perceive surrounding the hole, with light emanating from other sources having different polarization qualities. According to the scientists, this might give “a characteristic signature for the detection of wormhole geometry”.
Aside from the desire to uncover wormholes and establish their existence, as well as the possibility of interstellar travel, it is prudent to be able to distinguish them from black holes before approaching them. “If you were nearby, you would find out too late,” Nedkova told New Scientist. “You’ll get to know the difference when you either die or you pass through.”
The authors note that their results are based on a “simplified model of a magnetized fluid ring” around the black hole. More sophisticated models may show characteristics that can be utilized to identify wormholes from black holes in various ways.
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