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What is inside a Black Hole?

A black hole with an accretion disk surround it

The interior of a black hole is one of science's biggest mysteries to be solved due to the enigmatic properties it has with space and time as well as the laws of physics being challenged due to the mathematics we currently have that is incapable of solving the physics of the singularity and our limited observation of black hole visually. The gravity of a black hole is so strong that it defines the formation of itself when gravity has won over the battle with dark energy(expansion of the universe), meaning, when any matter in this universe has lost its equilibrium of being stretched and compressed by being overly compressed, the matter would turn into a black hole. This victory of gravity over space expansion makes the gravitational force of the black hole the strongest in the universe from which the fastest entity known in the universe, such as light cannot escape from a black hole. For this reason, we cannot observe what is inside a black hole with our senses due to light being unable to exit the black hole. The only way we could have an insight into a black hole is through theorizing it or discovering an equation that would help us solve it through mathematics. Nowadays, we have developed quite a few intriguing logical theories that might build pathways or aim to solve what is inside a black hole from which this topic will be going over such as a singularity, ring singularity, and Planck star.

Singularity

A singularity is a phenomenon in which a single one-dimensional point of matter in space is inhabited with the physical properties of being infinitely dense and small with the strongest gravitational force that has the capability of trapping light from escaping the pull into the singularity via a black hole. The settings in which singularities were and exist according to the current theories and knowledge we have from physics and astronomy are "The Big Bang" and "Black Holes". The initial singularity also known as the Big Bang's singularity is currently an unsolved and mysterious phenomenon because, with our limited knowledge of science and advancement of technology, we cannot tell how the initial singularity came into existence before The Big Bang since anything before the universe's formation, time was non-existent, therefore, we cannot appropriately theorize how the initial singularity was formed due to The Big Bang itself being major theory as well. Nevertheless, the formation of a singularity from the perspective of a black hole is much easier for physicists to theorize due to the gravitational force a black hole has as well as coming up with models and equations of how the singularities are formed. An example of an equation being used to prove the existence of a singularity is the Schwarzschild radius. The definition of the Schwarzschild radius equation is: if any matter known in the universe is being compressed to its Schwarzschild radius(compressed to its smallest possible size) the gravity of the matter overtakes the equilibrium the matter has with the expansion of space and gravity, and the matter would collapse into a singularity and become a black hole. To make the definition of Schwarzschild Radius more simple using an example of turning earth into a singularity and ultimately a black hole; "The Schwarzschild radius of the Earth is about the size of a marble. This is how much you would have to compress the Earth to turn it into a black hole. A black hole doesn't have to be very massive, but it does need to be very compact!". The theory of a singularity existing inside black hole is the most logical and accepted theory of what resides in a black hole due to astronomers and physicists stating: "The reason some people believe that a black hole contains a singularity is because Einstein’s theory of general relativity suggests it is the case. The reason that people believe this due to Einstein’s theory is because it usually yields very good matching experimental results. This is why the theory is trusted by so many scientists". Nevertheless, the premise of the singularity is still a theory and we have no valid confirmation of singularities existing inside black holes due to us not being able to observe inside a black hole visually or from technological data.

Ring Singularity

The Ring Singularity is a phenomenon that accepts the existence and theory of a singularity inside a black hole, however, with the condition of the singularity being stretched and taking the form of a ring shape inside a black hole if the black hole is rotating. This theory also spurs many other theories that could reside within a black hole such as wormholes and an inner horizon. The wormhole conjecture of a Ring Singularity is "According to the math of Einstein's theory of general relativity once you pass through the ring singularity, you enter a wormhole and pop out through a white hole into an entirely new and exciting patch of the universe". This theory might seem full of excitement to anyone, nevertheless, this theory has major flaws as to why it can't be a possibility in a ring singularity according to the laws of physics: "The interiors of rotating black holes are catastrophically unstable. And this is according to the very same math that leads to the prediction of the traveling-to-a-new-universe stuff". Moreover, the inner horizon premise in the ring singularity also opposes the wormhole conjecture due to the theory's conception of the ring singularity repelling matter from being drawn into the ring singularity. "The problem with rotating black holes is that, well, they rotate. The singularity, stretched into a ring, is rotating at such a fantastic pace that it has incredible centrifugal force. And in general relativity, strong enough centrifugal forces act like antigravity: they push, not pull". This combination of push and pull from the ring singularities gravitational property forms the inner horizon region inside a black hole from which it's an infinitely dense and thin layer of interior of a black hole similar to a singularity that serves as a limit to where matter can travel inside a spinning black hole until the black hole recedes to become to static in rotation from which the inner horizon recedes into the singularity. the premise of the ring singularity and the other premises it held are still theories and we have no valid confirmation of ring singularities existing inside black holes due to us not being able to observe inside a black hole visually or from technological data.

Planck Star

A Planck Star is a theorized astronomical entity based on the loop quantum gravity theory in quantum mechanics that is an extraordinary star with finite size in being very dense and small compared to a singularity that resides inside black holes. The Planck Star is a possibility in black holes if the loop quantum gravity theory is rectifiable by many hypotheses or evidence, or if the theory is validated to science and reality. However, the loop quantum gravity is not a very imposing theory in quantum mechanics as well as rectifiable with evidence or theories due to "Its main incompleteness is that its non-perturbative regime is poorly understood, and that we do not have a background-independent formulation of the theory. In a sense, we do not really know what the theory we are talking about is. Because of this poor understanding of the non perturbative regime of the theory, Planck scale physics and genuine quantum gravitational phenomena are not easily controlled". Therefore, we cannot go further into why Planck stars are a great possibility in black holes other than from what loop quantum gravity theory recounts about Planck Stars. Similar to a singularity a Planck star is formed when a matter is compressed to its Schwarzschild radius, however, the matter does not follow the same fate as a singularity: "It meets resistance. The discreteness of space-time prevents matter from reaching anything smaller than the Planck length (around 1.68 times 10^-35 meters). All the material that has ever fallen into the black hole gets compressed into a ball not much bigger than this. Perfectly microscopic, but definitely not infinitely tiny". The premise of the Planck Star is still a theory and we have no valid confirmation of Planck Stars existing inside black holes due to us not being able to observe inside a black hole visually or from technological data as well as being able to rectify the theory the loop quantum gravity.

References

1. “The Schwarzschild Radius.” Black Holes, hyperphysics.phy-astr.gsu.edu/hbase/Astro/blkhol.html. Accessed 7 Dec. 2023.
2. “How Big Is a Black Hole?” Hubblesite Special Feature, www.stsci.edu/~marel/black_holes/encyc_mod3_q3.html. Accessed 7 Dec. 2023.
3. “Does Every Black Hole Contain a Singularity?” Ask an Astronomer, 20 Oct. 2020, askanastronomer.org/does-every-black-hole-contain-a-singularity/#:~:text=The%20reason%20some%20people%20believe,very%20good%20matching%20experimental%20results.
4. Sutter, Paul. “What Happens at the Center of a Black Hole?” Space.com, February 9, 2022. https://www.space.com/what-happens-black-hole-center.  
5. Rovelli, Carlo. “Loop Quantum Gravity.” Living Reviews in Relativity, U.S. National Library of Medicine, 26 Jan. 1998, www.ncbi.nlm.nih.gov/pmc/articles/PMC5567241/#:~:text=Its%20main%20incompletenesses%20are%20that,we%20are%20talking%20about%20is.