Black holes are among the most elusive objects in the universe. As the name suggests, they're black (in the sense that light cannot escape them), and holes... Sort of anyway. The fact remains, unless they are accompanied by an accretion disk, they are almost impossible to detect. Researchers must look instead for how their immense gravitational influence influences their surroundings. In fact, we only just managed to take a direct image of a black hole three years ago, and it was a pretty huge deal.
There are many theories about what actually happens inside of supermassive black holes — like the one in the heart of the Milky Way Galaxy — and perhaps that will remain in the realm of theory for physicists, given the difficulties involved in studying them more closely. However, one rather interesting theory is that at least some black holes aren't exactly what they appear to be...
The Anatomy of a Black Hole:
There are three main components to black holes, and to understand how they might harbor wormholes in their centers, we must first look at what black holes are comprised of and what traditional physics says happens to matter which is "sucked in" to a black hole.
Primordial black holes are thought to have formed in the early universe, soon after the big bang. Stellar black holes form when a massive star runs out of fuel at the end of its life. No longer able to counteract the forces of gravity pushing down on its core through the process of thermonuclear fusion, the star's core collapses, causing a supernova, and the remainder of its gaseous envelope is cast off into space, forming a supernova remnant. The heavier the star, the more likely it is to collapse into a black hole. The smaller, less massive ones either become neutron stars, or white dwarfs (the category our Sun will fall into when it dies).
When the star's core collapses and is transformed into a black hole, it becomes a tiny, infinitely dense point, called a singularity. This is the point at which the escape velocity — how quickly matter must travel to escape an object's gravitational pull — exceeds the speed of light (the speed limit that photons, some of the most compact particles in the universe, can travel). Objects can remain in orbit around black holes without getting sucked in, but they must orbit outside of the event horizon, which is technically the point of no return. Anything that enters the event horizon cannot reach the speeds required to escape the object's grasp, thus it becomes the black hole's lunch.
Some, but not all, black holes have accretion disks, which are rotating disks within the ergosphere (the region outside the event horizon) of a black hole, where light and matter (such as gas and dust) are heated up, and thus emit large amounts of radiation — sometimes making these elusive objects detectable.
Now that we have a basic understanding of black holes, we can ask:
What Are Wormholes?
If you find black holes intriguing, wait until you read this next section.
Wormholes are similar to black holes in many ways. In others, they are diametrically opposite. For instance, black holes are believed to be one-way tickets to oblivion, whereas wormholes are tunnel-like objects that could drop you half-way across the universe in a couple seconds. They are essentially connected through "bridges" where spacetime folds in on itself, creating short-cuts through spacetime. In the simplest possible terms, pretend like you have a sheet of paper. Fold it in half, then stick a pencil through it. It's an easy analogy from there: you just traveled from one side of the paper to the other via a shortcut. You've just created the world's lamest wormhole approximation.
Given the fact that it would take thousands of years to travel to the nearest star, Proxima Centauri, from the Sun using current technology, and that our current understanding of physics generally precludes faster-than-light travel, wormholes might be our only hope of travelling beyond our galaxy. Although they purely theoretical, there are some physicists who argue wormholes can exist alongside our understanding of general and special relativity.
Turns out, the very physicist who came up with these crucial cornerstones of modern cosmology, the one and only Albert Einstein, was among the first to suggest wormholes could really exist. In fact, wormholes are often referred to as Einstein-Rosen bridges (named after Albert Einstein and physicist Nathan Rosen, who originated the idea in 1935, based on a special solution of the Einstein field equations).
There are a few different types of wormhole that have been proposed. Some could connect from one point to another from distances of over a couple of miles to a few billion light-years away (think Gargantua from Interstellar); others could lead from one universe to another; or from one point in time to another. Physicists have long speculated that these objects don't appear to contradict the laws of physics. The problem, however, is it's believed that any such structure would be extremely unstable, and it may be impossible to travel through and survive.
The main hypothesis suggests that, in order for a wormhole to remain open, stable, and trasversable, it must be made up of a form of exotic matter, which would, in theory, have negative energy that is repelled by gravity rather than attracted to it (the opposite of the way normal matter behaves). While this exotic matter remains purely hypothetical, other research suggests that wormholes might exist in the hearts of active galactic nuclei (AGN) ...
Is There a Way to Detect Them?
In a paper published late last year, researchers hypothesized that some of the supermassive black holes (SMBHs) in the center of galaxies may actually be so-called "wormhole mouths." Interestingly, the properties of SMBHs and wormholes are similar... Both are extremely dense objects with immense gravitational pulls. The main difference is, nothing can escape from a black hole, while light and other forms of radiation can move through a wormhole in both directions. Additionally, a wormhole would have two mouths, one at each end. Where they come together and intersect is naturally referred to as the throat.
The team suggested that when matter is streaming into the wormhole from both mouths, likely at extremely high speeds, given how great the object's gravitational pull would be, the particles would slam together and "spheres" of plasma would be ejected from both mouths at speeds coming close to the speed of ight. The plasma would also become extremely hot through this process, reaching temperatures of 18 trillion degrees Fahrenheit (10 trillion degrees Celsius) — and releasing immense amounts of highly energetic gamma-ray radiation.
This is thought to be the key to deciphering whether an active galactic nuclei actually harbors a black hole or a wormhole. The energies of gamma-rays emitted by these so-called plasma spheres would be about 68 million electronvolts, and an AGN gets neither hot enough or energetic enough to emit gamma-rays at this scale. We do occassionally see jets spewing gamma-rays from the mysterious objects in the heart of active galactic nuclei, but they travel parallel to the jets, instead of in a spherical flow pattern.
An observation of this type of radiation would serve as evidence of the existence of wormholes. By looking out into space and into the belly of the beasts, hopefully this research will guide physicists to a real, incontrovertible wormhole.