Black holes are mysterious but putative paradoxes that scientists continue to debate about. They are the supermassive remains of stars, which suck all forms of matter into them. They also pull light in, making a ring of illumination. Any matter that actually enters a black hole, cannot exit. However, there is no depth in the black hole. Therefore, when something enters the hole, it wouldn’t make sense for that form of matter to be stored inside. What exactly happens? This research document explores the unquestionably mysterious enigma that black holes are.

 Black holes were first conceptualized in 1783 by a man known as John Michell. He constituted a thought, talking about how if one fires a cannonball vertically, perpendicular to the earth, it would travel upwards for a while, stop, and then move downwards. He then spoke of how after a certain velocity, the cannonball would instead of falling, continue moving outwards and leave the orbit of the earth. This velocity is known as the escape velocity. The escape velocity can be easily described as the root of 2E divided by m, where e is the energy, and m is the mass of the object exerting gravity, in our case the earth.

 Michell then talked of stars like the sun, which have really large escape velocities due to their mass (root 2E by m again, here m is larger, hence v results as a larger value). He then introduced the concept of a star whose escape velocity is greater than the speed of light. We shouldn’t be able to see these due to the fact that they pull light inwards, and it never reaches us. Michell called them ‘Frozen Stars’, which have now become black holes. Since light cannot escape from black holes, it is not possible to actually see them. Only advanced telescopic systems can actually form an image of them. Recently, the supermassive black hole at the centre of the milky way, (Sagittarius A) was photographed using the event horizon telescope, which is a virtual earth-sized telescope that uses 8 colossal satellite dishes in 8 existing radio observatories on the planet to receive signals. A radio observatory, simply put, captures radio waves transmitted by celestial bodies to generate images of them and often deduces certain properties of theirs. Sagittarius A is 4.14 million solar masses, meaning that you could fit 4.14 million suns inside of it! (assuming, of course, that they survive{Not a very large chance}).

Now, the formation. When two neutron stars collide (extremely dense stars), the high amounts of mass cause thermonuclear fusion. Thermonuclear fusion is basically the fusion of two positively charged particles due to extremely high temperatures. The fusion keeps them together, but the two particles try rather hard to separate, which is why when they are split with mostly uranium, they generate high amounts of energy. These, when in high quantities, essentially collapse onto themselves, creating black holes.

Think of it this way. You hold a quarter-filled balloon. When you poke your finger through it, the latex stretches, and then comes out the other side, but, if the same is done from every possible angle, the balloon would compress, as air is a gas and may compress. Similarly, stars compress onto their core and “technically” push out the other side, and form black holes. 

Talking about size, most stars that burn out into black holes are about 15-25 times larger than the sun.  These are actually the more diminutive ones. Categorized as supermassive black holes, these ones are up to billions of times as large as the sun. interestingly enough, a black hole that is about 1 solar mass would take 10 raised to 67 years to evaporate, which is much longer than the present age of the universe (10000000000000000000000000000000000000000000000000000000000000000000 years), so imagine the scale of regular, or even larger ones! If one were to dissect a black hole, one would find that it would consist of 3 major parts. Outside the black hole, there is quiet space, meaning no disruptions in the fabric of spacetime. Following that is the ergosphere, which is a slight inwards curve. The ergosphere somewhat represents a giant depression in the fabric of spacetime. Its name was proposed by a man called Reno Renneli, and a fun way to visualize it, (not Renelli of course, for that we have google.) is a heavy object on a mattress. There will be a point where a small ball upon being placed shall begin to roll inwards, and after that is a point where it shall speed up and finally collide with the object. The region where the ball begins to roll inwards at a slow rate is similar to an ergosphere. Within the ergosphere, you may manage to escape the pull of the black hole, but the escape velocity shall be relatively lower than the speed of light, meaning if you were a particle that escaped from the Large Hadron Collider and stumbled your way into a black hole, technically you should be able to escape if you enter just the ergosphere.

Beyond that is the event horizon. Anything that enters the event horizon is doomed to perish and will never make it back out the way it entered. A fascinating concept can be mentioned here, known as light cones, which are another aspect of Einstein’s Relativity. Light cones can be simply put as a path, or a railroad that an object must follow. You can visualize it as a car with its headlamps approaching a black hole. Its headlamps would emit light, and before the car enters the event horizon, its light does, and hence the light would curve into the event horizon, basically forcing it to stick to the path of the light, as it represents the car’s future, binding it to enter the event horizon, and doomed to a very brutal death. Yikes.

The way relativity describes it, is that a light cone is emitted by a single object in the fabric of spacetime, and it represents its past and future, so essentially the light cone can help us deduce whether the object shall enter the event horizon or not. If right upon the horizon, it shall remain stationary. Within the event horizon, one would find the singularity, the point at which all mass that enters is compressed. The point from the singularity to the event horizon is known as the Schwarzschild radius. The Schwarzschild radius can be calculated as follows,  r=2GM/c2 , where r is the radius, g is the gravitational constant, and m is the mass of the object. Essentially, the radius is what we can call the distance between the singularity to the event horizon. Note that we use the main event horizon for this, not the Cauchy horizon (more on those later). The same can further be used to calculate the volume, however, that is fairly irrelevant as of now.

If we go deeper into the anatomy, a black hole would have an outer event horizon, and an inner event horizon, also known as a Cauchy horizon. Inside are the time geodesics, and outside are space and time geodesics, meaning that once you enter the Cauchy horizon, you are no longer travelling through space, but through time. A geodesic is essentially just the shortest path from point a to point b, on the surface of a sphere. When we warp spacetime, we create a depression and to cross that, you would pass through a geodesic, which is a parabolic line on the curve’s surface. What is meant by a spacetime geodesic, is a geodesic where you are moving through the fabric of spacetime, where space and time are directly related to one another. Once you enter the Cauchy horizon, space-time is warped to such a large extent that time ceases to exist for you, however, time continues as it is. So while you technically are suspended in frozen time, it still exists, so according to the rest of the world, you move in space, but through time, almost as though time is no longer a dimension, but an obsolete and infinite gate. (this may be a little confusing, but that is alright as this is still a very abstract concept in the theory, and for those of you in the science club, our club’s name is another further advanced concept of space-time geodesics.)  Just beyond the Schwarzschild radius is the photon sphere. This is an area where the gravity is so perfectly balanced that photons orbit, and are neither in nor out of the black hole. The light shall be trapped here for a very long time, but not forever due to instability in the orbits. If you go back to the introductory paragraph, I state that black holes have no depth, however, I appear to contradict myself. Truth is, the ‘depth’ I speak of here is actually warped spacetime, possibly in the fourth dimension, which we cannot call a certain depth as we live in an observable reality of three dimensions. Placing a heavy ball onto a mattress or trampoline is a fun way to envision this within our restricted three-dimensional reality. We can then place a lighter one close by, and observe as it rolls into the depression created by the ball with larger mass and inertia. In the same way, objects with large masses create depressions in the fabric of spacetime, which is essentially the theory of general relativity at a very basic level in layman’s terms. The only marginal difference here is due to the lack of many objects and providing enough time for physics to behave normally, the lighter ball rolls in straight away instead of orbiting, but nevertheless, it’s an interesting experiment. There is actually a really invigorating website with a simulation you can create, on NSTMF, called NSTMF Gravity, where you can create objects and observe as you add more to put them into each other’s orbits.

Kerr black holes are another rather interesting type. These are ones said to have angular momentum, but not directly on the singularity, meaning that a ring singularity would be formed, resulting in a wide stretch upon contact. When a star dies, its angular momentum is conserved, and the moment of inertia decreases due to a shrink in the radius due to a lack of spread-out mass. Even a small amount of angular momentum shall be conserved due to the law of conservation of momentum. When the mass is compressed, a similar situation to figure skating arises. When the skater pulls their arms inwards upon spinning, they increase their angular velocity, and the momentum is described as angular velocity into the moment of its inertia. (inertia is the ability of an object to resist changes in motion). When the star spins, it’s an outer edge in (let’s assume here) 1 year, spins 100 miles. When the star shrinks, the velocity is retained, but the distance shrinks to maybe 0.001 meters, and the same distance shrinks, hence a lower value of s when divided by t is a faster velocity.  There is a theory that Kerr black holes have opposing “white holes”, and when something passes through a ring singularity, it is spewed out of the white hole in a possibly different dimension, or universe. Obviously, we have no proof of this however one never knows!

Within black holes, all laws and rules of physics as we know it breaks down. Einstein’s theory of general relativity mentions how objects distort the space-time continuum (or the fabric of space-time) around them, but if the curves become infinite, the rules of physics and space-time stop applying.

In 1972, a Princeton graduate Jacob Berkenstein made a suggestion, that when a black hole is formed, it settles to a stationary phase, described by its mass, angular momentum and electric charge. Other than this, it holds no information regarding what it has collapsed from, meaning one could not identify information about the star from a black hole with a high degree of accuracy. We do not know with any certainty which type of star the black hole was made of. Would this mean that there could be an infinite amount of possible predecessors to the particular black hole? As John Wheeler put it, “black holes have no hair”. Unless we leave out quantum mechanics, no. Heisenberg’s uncertainty principle comes into play here, which states that an object’s position and velocity cannot even in theory be measured at the same time, which is why CERN’s LHC accelerates particles at a stated value of 99.998% of the speed of light. This means that at a quantum level due to that fuzziness of jumping particles, we can never determine the facts for what they are with complete certainty. The equation Δx Δp  ≥ h/4π can be used to derive the uncertainty in the unit of the value, so if the question speaks of cms, the uncertainty is cms, if it is moles, the uncertainty is mole, same for all other units like candela joule etc. So thanks to Heinsberg, while it may not be possible to determine the possibilities, we can say for sure that the black hole could only be made of a finite number of possible scenarios.

What Berkenstein said was that with these finite combinations, we could measure the entropy of the black hole, which is the thermal energy per unit temperature. The amount of entropy also shows the degree of molecular disorder or randomness of particles. We know that higher entropy means more energy Thanks to this, we can assign a few parameters to black holes, such that they may exist.

As we now know, we cannot tell what is inside a black hole from its outside, meaning that they conceal a lot of information. The mystery posed was, that if the holes have an amount of entropy, they must release thermal energy in the form of radiation! Stephen Hawking identified this, and it is now referred to as hawking radiation, which is the radiation released by black holes. Do note, that this radiation has not yet been detected, however, the theory is concrete and hence is not challenged very much.

A very interesting aspect of this theory is its linkage to quantum theories. Quantum states a lot about antimatter, which essentially is an antiparticle to presently existing matter. Just as a number removed from a root can be both positive and negative, each proton must have a negative positron, and so on. The linkage is, that if one particle from this twin set falls into the black hole, the other particle might be left alone and will not annihilate and balance, but instead either follow after its doomed buddy or exist by itself, which is a personal theory of mine on Baryon Asymmetry. If the early universe consisted of many extremely dense black holes, (possibly very small), then perhaps these possibly unstable antiparticles were somewhat repelled from the black holes. Only regular matter would fall through, meaning antimatter may be immune to black holes.

The reason identifying this radiation is hard is because large black holes release too little, ergo we as humans must find one the size of, a mountain. This is very hard due to the fact that these sizes of black holes are too rare, and the ones that we find are too far out. The way we identify and locate black holes is by observing matter around them, and how it acts. We use ultraviolet telescopes to observe the way gasses invisible to the human eye behave in the vicinity of a black hole. X-ray telescopes show us how particles react to a black hole. 

Once the mass is emitted, the black hole loses some of it in the form of thermal radiation, meaning that at some point it shall be completely devoid of any mass, but the question that is then posed is what happens to the random objects that wandered into the event horizon? Over here we are not talking about Kerr’s black holes. Logically, it only makes sense that this has now been converted to thermal radiation, however, the mass seems to have disappeared. Over here, we can now discuss the DeBroglie wavelength, which is equated and quantified with the equation λ = h/p = h/mv. This shows us how certain objects’ quantum effects can be observed, and this happens when a black hole’s Schwarzschild radius is equivalent to its event horizon. Back to the information paradox, a common theory is information can be retrieved no matter what you do to it, if you burn it you can clean and in theory rejoin the ash fragments, but with a black hole that ceased to exist, this would apparently not take place, but some believe if the wavelength of the hawking radiation is heard, the information may be emitted out as it is hidden there. A little snippet from a Reith Lecture by Stephen Hawking goes like this: “The scientist Kip Thorne and I had a bet with another scientist, John Preskill, that information would be lost in black holes. When I discovered how information could be preserved, I conceded the bet. I gave John Preskill an encyclopedia. Maybe I should have just given him the ashes.” So essentially, a black hole may actually allow the matter to exit instead of being the eternal prison it was thought to be. Excuse me for switching to philosophy for a moment, however, if you ever find yourself inside a “Black Hole”, know that there shall always be a way out.

It is said that if any form of organic matter goes near a black hole, the part of it that is closer to the hole would be accelerated at a higher pace and would then be stretched and elongated forever, leaving you with a noodle-like shape towards the end. an extremely long and thin noodle. This is scientifically coined with a very fancy term, which took a lot of thought; “spaghettification” and bifurcation. As a limit is attained, the matter would split, and the two new noodles would be spaghettified, then they shall bifurcate again, and so on. If it offers any consolation, even though you might not live to see it, your body’s remaining matter once decimated by a Kerr Black Hole might actually move off to another universe, and land in the food of some alien, resulting in a fragment of your being existing as a life form in another universe.