Physicists have discovered a strange twist in spacetime that can mimic black holes – until you get too close. Known as ‘topological solitons’, these theoretical folds in the fabric of spacetime could be lurking all around the universe – and finding them could advance our understanding of quantum physics, according to a new published study. April 25 in the magazine Physical examination D.
black holes are perhaps the most frustrating object ever discovered in science. Einstein’s general theory of relativity predicts their existence, and astronomers know how they form: all a massive star needs to do is collapse under its own weight. With no other force available to resist him, gravity keep firing until all the material in the star is compressed into an infinitesimally small point, known as the singularity. Surrounding this singularity is an event horizon, an invisible boundary that marks the edge of the black hole. Anything that crosses the event horizon can never get out.
But the main problem with this is that points of infinite density cannot really exist. So while general relativity predicts the existence of black holes, and we’ve found many astronomical objects that behave exactly as Einstein’s theory predicts, we know we still don’t have the complete picture. We know that the singularity needs to be replaced with something more reasonable, but we don’t know what it is.
Related: Are black holes wormholes?
Understanding this requires an understanding of extremely strong gravity on extremely small scales – something called quantum gravity. To date, we don’t have a viable quantum theory of gravity, but we do have several candidates. One of these candidates is string theorya model that suggests that all of the particles that make up our universe are actually made up of tiny vibrating strings.
To explain the wide variety of particles that populate our universe, these strings cannot simply vibrate in the usual three spatial dimensions. String theory predicts the existence of extra dimensions, all curled up on an incredibly small scale – so small that we can’t tell those dimensions are there.
And this act of shrinking extra spatial dimensions to incredibly tiny scales can lead to some very interesting objects.
In the new study, the researchers proposed that these extra compact dimensions may give rise to defects. Like a crease that you simply cannot remove from your shirt, no matter how much you iron it, these flaws would be stable and permanent imperfections in the structure of space-time — a topological soliton. Physicists have suggested that these solitons will probably look, act, and smell like black holes.
The researchers studied the behavior of light rays when they passed close to one of these solitons. They discovered that solitons would affect light in much the same way as a black hole. Light would bend around the solitons and form stable orbital rings, and the solitons would cast shadows. In other words, the Famous images from the Event Horizon Telescopewho zoomed in on the black hole M87* in 2019, would look almost exactly the same if it were solitons in the center of the image, rather than a black hole.
But up close, the mimicry would end. Topological solitons are not singularities, so they do not have event horizons. You can get as close to a soliton as you want, and you can always leave if you want (assuming you have enough fuel).
Unfortunately, we don’t have any black holes close enough to dig into, so we can only rely on sightings of distant objects. If ever topological solitons were discovered, the revelation would not only be a major insight into the nature of gravity, but it would also allow us to directly study the nature of quantum gravity and string theory.