Why Black Hole Environments Are a Lot More Complicated Than We Thought

Black

hole

s are one of the most amazing aspects of space. To begin with, they are not actually objects, they are the result of the extreme warping of space-time. And because of this warp, some really strange things start happening around him that will change his perspective of the way the universe operates around him. Some things are so strange that you might not believe them to be true, if it weren't for the solid mathematics supporting their existence and properties, and the growing evidence that the mathematics is correct through observations in our own universe. I'm Alex McColgan, you're watching Astrum, and in this video, we'll explore the unexplorable.

Join me on this journey as we try to understand the strange science of how a

black

hole

forms, what happens around it, and explore what might actually allow for an escape from the most inescapable prisons in existence. I hope that by the end of this video I have earned your like and subscription. Black holes come in a variety of sizes. The smallest

black

hole observed is about 3.8 solar masses. On the other side of the scale, we find black holes that have existed almost since the beginning of the universe, black holes that weigh billions of solar masses.

These giants are not only massive, but also huge; They easily fit the entire solar system within the diameter of its event horizon. The black holes created today are the final stage in the life cycle of particularly massive stars. When such a star is born, it essentially balances under the weight of two forces. The first is gravity, which pulls its mass towards its center. Deep within the star, hydrogen atoms are crushed against other hydrogen atoms with such force that they combine to form a denser element: helium. This new atomic structure actually needs less energy than when it had two separate, individual hydrogen atoms, so the excess energy is released.

This released energy is the second force. It radiates from the center of the star in the form of heat and light, counteracting the force of gravity pushing inward. In this state, the star will remain relatively stable until such time as the reaction begins to stop when it runs out of hydrogen fuel. . If the star is massive enough, once hydrogen begins to become scarce, the star will combine the newly formed helium into even denser materials, such as carbon, neon, and eventually oxygen and silicon. But then he starts fusing the Iron. The problem with iron is that it doesn't save energy in its new form, so it has no extra energy to release.

It simply settles into the star's core and grows larger. Without energy pushing against gravity, the scales tip very quickly. The energy of this collapse is astonishing, but the strength depends on the original mass of the star. Like a hammer hitting an anvil, the star's mass rushes toward the core with such force that the rebound from that blow is what we call a supernova. Matter and energy are ejected across the universe from the rift, in one of the largest explosions possible, producing elements even heavier than iron, up to uranium. And what remains of the star? Well, that depends.

If the mass of the star and therefore the force of the blow were too small, what remains is a neutron star: a small ball of matter about 25 kilometers in diameter at most and yet so densely packed with mass equivalent to one million Earths. . But what if the mass and therefore the force were large enough? Physics as we know it fails and we are left with a black hole. When you see an image of a black hole, the black sphere you are looking at is not actually the black hole itself. Scientists theorize that the true shape of a black hole is probably even smaller and denser than that of a neutron star.

In fact, it is likely infinitely small and infinitely dense: a Singularity that emits forces that warp time and space itself. However, we don't know. And the reason we don't know is because of something called the event horizon. All objects with mass exert gravity. We have known this since the days of Newton. However, when Einstein came out in 1915 with his theory of general relativity, a contemporary of his named Karl Schwarzschild reasoned that there could be objects that were so massive that they could create enough gravity that light itself could not escape. And if even massless light photons couldn't get out, nothing could.

When you look at an image of a black hole, you are not looking at the black hole itself. You're looking at the event horizon around you: the line of demarcation where gravity has become so powerful that light can no longer leave. There is nothing but darkness. Now, their effect on space is one thing, but black holes also impact another aspect of the universe, time itself. You see, according to Einstein, space and time are inseparably connected, and mass warps space-time. With the infinite point mass of the singularity, spacetime is stretched so much that the event horizon also marks the point where time stops.

Within the event horizon, space and time basically cease to exist, a place where there is no "where" or "when." This produces an interesting phenomenon for an outside observer watching matter fall into a black hole. From his perspective, as matter approaches the black hole, it will slow down until just before the event horizon, where it will stop completely. You will never see it cross the event horizon, there will be no satisfactory absorption. Instead, the matter will gradually fade away until you can no longer see it. When it was first theorized, astronomers and physicists weren't sure if black holes were actually real.

Only 40 years later was the first evidence of a black hole recorded. In 1964, using newly developed X-ray satellites, scientists noticed an object in the Cygnus constellation that appeared to be emitting a large amount of They were surprised because if it were a star, it should emit visible light in addition to X-ray radiation. Scientists called this object Cygnus X-1. In 1970, as telescopes advanced, they noticed that whatever Cygnus X-1 was, it had formed a binary orbit with a star in its system, and this helped scientists calculate its mass. They discovered that this invisible object was 15 times

more

massive than the Sun.

Since the densest neutron star had an upper limit of 3 times the mass of the Sun, scientists realized that it was probably the first black hole discovered. Since then we have discovered many black holes. Supermassive galaxies seem to exist at the center of galaxies, and we have even managed to take photographs of some, dark spots against a swirling ring of matter that surrounds and falls into them: their accretion disk. This is how black holes can still be detected using X-rays. While black holes cannot emit visible electromagnetic radiation themselves, the It is heated to millions of degrees Celsius through intense friction.

Black holes without infalling matter are basically invisible, with no bright accretion disks to detect. The exploration of black holes is still a developing field in physics and there is still much to learn. From what we've learned so far, you might wonder if a black hole could one day stop being a black hole or will it grow forever until there is no matter or radiation left in the universe. It seems. However, in 1974, in his article titled “Black Hole Explosions?”, physicist Stephen Hawking postulated that there was actually a way that energy, and therefore mass, could come out of a black hole.

But to understand why, we have to delve into an extremely strange theory. We need to examine some principles of quantum mechanics. But first let me ask you a difficult question: what is “nothing”? Imagine for a second a piece of space with nothing in it. It has no atoms of space dust, nor even radiation passing through it. As far as can be seen, nothing exists within it. And yet, is there really nothing here? Well, no. There is something fundamental here, and we can say that it is so when a ray of light passes through it. If you are familiar with the properties of light, you know that light is actually waves of electric and magnetic charge that constantly propagate past each other in straight lines.

However, let's look at the word "wave." A wave in the sea is the propagation of energy moving through water. If you were to observe an individual particle of water, it doesn't really go anywhere except in a circle, and yet, because it passes energy to the atoms next to it, the energy travels toward the shore in a constant motion that reaches until the end. the beach. Similarly, a sound wave moves by passing energy between air particles, and each particle only moves a little bit, gets energized, and then passes that energy to the next particle in line. But in our vacuum of space, where there is nothing in it, where our photon of light travels in waves, have you ever stopped to wonder what exactly “wave” is?

This alludes to something fundamental that exists even in nothingness, a fabric that constitutes all of reality itself. Quantum physicists call this “something” a quantum field. Quantum fields are difficult to understand, but they are inescapably important when it comes to understanding the ultimate fate of a black hole. So how are quantum fields and exploding black holes related? Going back to Hawking's paper, Hawking hypothesized that black holes would release energy slowly over time, in initially small amounts. Since energy and mass were two expressions of the same thing according to Einstein's famous e=mc2 equation, this inevitably resulted in a reduction in the mass of the black hole.

However, as the black hole shrinks, the rate of energy release would accelerate, becoming faster and faster until in the final moments of the black hole's life it would release a burst of energy that was truly gigantic in its scale. , before disappearing completely. . But how can this be true? It is well known that an event horizon is inescapable, so how could radiation come out of it and eventually cause such a black hole explosion? The answer is strange and based on unintuitive ideas in quantum theory that go completely against our everyday experience. But if it's true, I hope you're prepared for the universe to be a lot stranger than you first

thought

.

But to begin to understand Hawking's theory, we need to understand the idea of ​​quantum fields. Remember, light moves like a wave even through a completely empty space of space, revealing that there must be something existing even in nothingness, otherwise light would not be able to shake it. Scientists call this fundamental fabric of reality the quantum field. In fact, they believe that there are several quantum fields, all overlapping each other and covering every part of the universe, whether past, present or future. Each quantum field defines a particular type of something. One field could define all the electrons in existence, while another could define the quarks that make up an atom.

Where nothing can be found, the quantum field is relatively silent. Think of it like a guitar string that hasn't been strummed or a graph that has a value of zero. But wherever in time and space mass or energy can be found, the quantum field resonates at that point, and when the resonance reaches a certain threshold or quantity, the universe expresses it as, say, an electron or a photon. It is important to note that in this theory resonance is not simply reacting to a piece of matter, it is matter. An electron is nothing

more

than a resonant section of the quantum field that defines electrons.

This is true for all energy, and also for all matter; After all, according to Einstein, energy and matter are two sides of the same coin. The entire universe you see around you is resonating quantum fields and nothing else. In this way, the theory portrays the entire universe as a song being played in these fields, which I think is a pretty beautiful image, at least. But why does this matter? Why is it important to define the universe this way? Well, because of an idea in quantum physics called the Heisenberg uncertainty principle, sometimes the strings of the universe start to strum.

Without delving too deeply into this aspect of quantum physics, essentially when we look at really small objects on the atomic scale, it becomes impossible to know too much about them. For example, it is not possible to know the location and direction of travel of an electron at the same time. Because it's so small, as soon as you try to determine the location of an electron, it bounces off whatever you're trying to use to measure it, so you can no longer be sure.of your direction of travel. If you know its address, according to this principle, you cannot know its location.

This is not just because our measurement methods are not good enough, but because of some fundamental laws about the nature of the universe itself. According to the Heisenberg uncertainty principle, not everything about particles can be known at the subatomic level. But when you apply this principle to quantum fields, it gets strange. Quantum fields fluctuate everywhere, and according to the Heisenberg uncertainty principle, particle-antiparticle pairs can appear and disappear. The how and why get

complicated

, but basically the universe allows it as long as they only exist for a very short period of time governed by relationships of uncertainty.

You might think this can't be a real thing. Matter does not simply arise. Surely we would have realized it by now. However, in an experiment conducted by Hendrick Casimir, evidence was found to suggest that this could actually happen. Casimir took two plates of conductive metal and placed them close enough together that only certain sizes of smaller virtual particles could appear between them. This limited the number of such particles that could appear. But since all kinds of particles could appear on the outside of the plates, this meant that there was a difference in the pressure exerted on the two sides of each plate.

Theoretically, the greater the pressure exerted by the greater number of virtual particles on the outside of the plates should push the two plates together, and in the test this was demonstrated. You might think that particles that appear out of nowhere seem to defy the laws of conservation of matter. You would be right. So, to balance the scales, every time a virtual particle appears, a second particle also appears to pair with the first particle. But while one of the particles is matter, the other is antimatter. A “1” and a “-1” on our bar chart, thus keeping the total at 0.

The universe is happy. And on top of that, these fluctuations in the quantum field quickly collide with each other and annihilate each other, removing them both from existence again, so we normally don't have to worry about them. As a side note, there is a theory that antimatter is simply matter moving in the opposite direction through time, but that's a level of weirdness we don't need to get into here. The important thing is that quantum fields constantly resonate and constantly cancel each other out. That's why, for the most part, empty space is empty. However, what would happen if you stopped resonating just some of those fields?

And that's where black holes come in. Black holes act a little like putting your thumb on the guitar string of the universe. Because of their event horizons, certain resonances in quantum fields are damped, while others are not. Hawking imagined drawing a line through time, in a patch of space where a black hole had been born. He imagined a quantum field that resonated along this line, extending from before the black hole existed to the future afterward. Before the birth of the black hole, everything is normal. All quantum fields resonate freely and can cancel each other. However, the appearance of the black hole's event horizon changed the curvature of space, and outside of it, Hawking realized that certain pulses were now missing their opposite numbers.

By looking at the mathematics, he realized that not everything was canceled after the black hole formed. In fact, outside the event horizon, moving away from the black hole, he found resonances that perfectly matched the shape of the thermal radiation receding into space. Radiation is energy and energy cannot be formed from nothing. Since the black hole was creating this radiation, it would have to pay the price. Each portion of Hawking radiation would thus coincide with an equal amount of energy lost by the black hole, which would eventually reduce it to nothing. If it exists, Hawking Radiation is something like money appearing spontaneously outside a bank, while inside the bank the money in its vault disappears.

It is also extremely difficult to prove, as Hawking predicted that this radiation would be cooler than the cosmic background radiation that fills the universe and would have a wavelength as long as the black hole's own event horizon. Because some black holes have event horizons the size of solar systems, we have no way to detect this type of radiation. We'd only really see it once the entire universe had cooled down and died, so there was nothing else to get in the way. Which would probably mean we would no longer be around to do the screening. However, despite objections to it, the mathematics behind Hawking radiation appears to be sound.

And scientists have recently taken steps to demonstrate it in the laboratory. At the Technion Institute of Technology in Israel, researchers studying Hawking radiation came up with an idea to solve the difficulty of measuring a black hole in real life. They did this by creating an analog: a "sonic" black hole that would mimic the properties of a real one. They relied on the fact that sound moves much slower than light, so it is much easier to create a medium that moves faster than sound. When it moves, sound waves traveling in the same direction can never fully escape.

Interestingly, Hawking's math worked for these sonic black holes as well as for gravity-based ones, so Hawking radiation should be detected in them. After repeating their experiment 97,000 times over 124 days of continuous experimentation, the researchers detected multiple instances of Hawking radiation and saw that it matched predictions from Hawking's model about how his radiation might behave. Although this doesn't prove that Hawking radiation is definitely real for real black holes as well, the fact that Hawking's math worked for this sonic analog is a strong implication that he might be onto something. Hawking radiation could be real. So if you fell into a black hole, would you ever be able to escape?

Probably not. However, if you waited until almost the end of the universe, the black hole may simply radiate hawkish radiation until the mass and energy that made up your existence were completely removed from the interior of the event horizon. Does that count as escaping? That's probably not so appealing to you. It's probably best to just not go in. And that's not the only strange thing about black holes. Its existence implies something quite worrying about our own reality. When you are walking on the beach and you leave a footprint in the sand, you have no doubt that it was your foot that caused the footprint.

The order of causality is quite clear here, to the point that it seems ridiculous to even have to state it. You made the print. The print didn't make you. But what if it were? What if I told you that on the cosmological scale, the fundamental relationship between foot and footprint might be a little more confusing than you would intuitively think? And surprisingly, due to the nature of black holes and falconry radiation, there is some evidence that this could be the case. But to begin, we will need to observe a principle called relativity. But no, not that relativity.

Galilean relativity. First described by Galileo Galilei in 1632, the idea of ​​this form of relativity is that there is no difference between being completely still and moving at a continuous speed. Imagine that there are two rooms, one on a ship and one on land. Both are soundproofed and have no windows. Imagine that the sea is calm, so there is no rolling. The only difference between the two rooms is that one moves and the other does not. Can you tell the difference between the two from the inside? You might think that you would be able to feel the movement, but you don't.

For example, right now you are traveling through space at 110,000 km/h due to the Earth's motion around the Sun, and yet if you were sitting at home watching this, you would probably have said that you weren't moving at all. . . In fact, Galileo realized that no test could be performed to distinguish between the two scenarios. He even discovered that if you dropped a ball on the ship, from your perspective it would appear to fall straight down, even though from the perspective of a person on land it would appear to fall diagonally. Galileo realized that if you eliminate all frames of reference, let's say you're in space, there's no way to know if a planet is moving toward you or if you're moving toward a planet.

According to relativity, both are equally valid interpretations. You may have noticed this if you've ever looked out the window of a train just as another train suddenly passed by and quickly passed you. Although both trains are going forward, the other train is going faster than yours, and since you no longer have a frame of reference to compare your motion with, it might seem like you're suddenly going backwards. Einstein took this idea further with his equivalence principle. Here he revisited the idea of ​​two rooms, but this time making an observation about gravity. If you were inside a windowless room floating in the vacuum of space and someone started accelerating your room in the "up" direction (for example, by strapping a rocket to the bottom), if the rocket accelerated at just the right speed, then you would feel identical. as if you were standing in a room on the surface of the Earth.

In other words, there is no way to distinguish between the acceleration caused by gravity and the acceleration caused by a rocket, assuming you can prevent the rocket from hitting you with all its roar, of course. Both principles are based on the idea of ​​inertia: that objects do not like to move if they are simply left alone, and they do not like to stop moving once they have started. Every time you want a mass to do something different from what it is doing, you must apply a new force to it. Otherwise it will remain inert. But why would the man in the room with the rocket feel as if he were under the effects of gravity?

Or perhaps a better question: why on Earth would we feel as if we were being accelerated upward by the effects of a rocket? The Earth isn't expanding in all directions at once, pushing us with it, is it? While this is true, Einstein realized that the two felt similar because they were both the same. A form of acceleration. However, there is another form of acceleration that better explains how gravity works than simply applying a force to an object to push it like a rocket does. Consider this spinning fairground ride. If you've ever been on a ride like this, you know the power of changing direction as a form of acceleration.

When you stand against the wall of the ride, once it reaches speed, you feel a constant force pressing you against the wall even when the ride is spinning at a constant speed. This is because its mass tries to move in a straight line at each point along the path, but the curvature of the path forces it to alter its direction. The battle between your inertia trying not to change what you are doing and the wall trying to alter your direction of travel manifests as the force you feel. And as far as acceleration goes, there's not much difference between the ground beneath you accelerating you up and you trying to accelerate down.

Einstein realized that this form of acceleration (acceleration caused by a curved path) was the best explanation for gravity. He came up with the theory that matter and energy cause a deformation in the space around it, somewhat like a ball might bend the surface of a taut sheet of rubber on which it is placed. The greater the mass, the greater the curvature. And once space was curved, any object that tried to travel through it would be deflected by that curve. In the words of physicist John Wheeler, “space tells matter how to move. “Matter tells space how to curve.” For small masses, this curvature in space would be very slight, but in dense masses this curvature could become so great that it would be impossible for an object that came too close to it to escape from it.

These are the conditions we find near a black hole with its event horizon. So, going back to our first footprint and foot analogy, if a black hole is the foot, the curvature of space around it is the footprint. It's interesting to see all of this in action and understand how Einstein came to conclusions that have been almost universally validated by scientists even a hundred years later. But so far there is nothing particularly strange about all this. Understanding the exact mechanisms behind all of this doesn't make it any stranger. The black hole tells space how to curve, and once curved, any object that moves near it is told how to move.

Nothing here is outside our expectations based on day-to-day observations. But when we start looking at Hawking radiation, something very happens.strange. But the most important thing to keep in mind for the purposes of our current video is that it is not local. This means that it appears not from the black hole itself, but from the area of ​​space surrounding it. To be clear, I don't mean beyond the black hole singularity, but even within the black sphere. That's hard to define anyway, space as we know it doesn't exist there. Remember, the black ball you see here is simply the demarcation point between inescapable curvature and avoidable curvature: the event horizon.

I'm not even referring directly to the event horizon, although that is sometimes how this theory is presented. Sometimes people talk about two particles arising right at the event horizon, with the antimatter particle right inside it so it falls, while the normal particle is right outside it and so it escapes. This is not what is happening. Instead, the region of space in which this radiation can appear is several times the size of the event horizon, a distance up to billions of kilometers away. And when the largest black holes we have can comfortably accommodate multiple solar systems side by side within their event horizon, the idea that a photon of radiation could re-exist at this distance outside the event horizon is crazy. .

It happens even in a place where there is literally nothing there. In short, it's not so much that Hawking radiation comes directly from the black hole. Instead, it arises from the curvature of space that is creating the black hole, and can occur quite far from the black hole itself. But if that's true, then things work completely opposite to what we might expect, as you'll see in a moment. Consider what happens in this order. As energy leaves the curvature of space, the curvature decreases due to something known as conservation of energy. And as this reduction in curvature occurs, the black hole shrinks.

This is crazy. This is as if the footprint becomes smaller and therefore the foot shrinks accordingly. It feels very bad. Things can't possibly work that way. And yet Einstein hinted that such a thing might be possible. In one of his equations he stated that the curvature of space-time was proportional to the mass-energy of an object. But proportional is not causal. There is no presupposition of one causing the other in this relationship. We're comfortable with the idea of ​​changing the mass and therefore changing the curvature, but it works just as well if you go the other way and change the curvature to change the mass.

If this is true, then it suggests a universe where mass is simply a projection caused by the curvature of space. When you turn on a light, you look at an object (for example, your hand) and it creates a shadow on the wall, the shadow is a projection caused by the existence of your hand interacting with the light. Normally, in this analogy, you could be forgiven for thinking that we are the hand. It is our mass that creates the curvature of the space around us. And yet, do we really know that it doesn't work the other way around?

Are we simply projections, shadows on the wall of the universe brought to life by something much more fundamental happening in the curvature of space-time, and yet we walk around thinking we are the real thing? We really don't know. Since all you know is the reality you experience, you would have a hard time being able to distinguish between the two scenarios. But if relativity has taught us anything, it is that if there is no way to differentiate two situations, then we cannot completely rule out that we are in one and not the other. Either that, or the two could be more linked than we

thought

.

Of course, this is obviously all just a theory. There is no hard evidence that Hawking radiation is even real, although there have been some experiments that hint that it might be. But this is something interesting to think about. And even if reality is proven to be a projection, it won't affect your day much. You will continue to think and feel, and that is more than enough reason for you to continue doing what you are currently doing. But it is an example of how when we begin to examine the fundamental elements of reality by exploring the strange warping effects of black holes, we can question assumptions about our own nature.

After all, when you ask the question "Am I real?" and the answer is "It's not safe", that's more than a little worrying. Either way, black holes affect our reality and affect our universe. And not only because they absorb everything within their reach and give nothing back. They are the end, the final destruction of the universe. And yet, what if I told you that they could actually turn out to be our salvation? Black holes could provide the answer to traveling faster than the speed of light and solving the energy crisis in ways we couldn't even have imagined until recently.

And, as expected, they do so by altering the fabric of reality itself and completely countering my expectations of physics. Maybe we have been thinking wrong about black holes? But understanding how a black hole ignores the usual limitations for traveling faster than light (and does so in a way that you can benefit from it without having to enter a black hole's event horizon) and how it produces almost unlimited energy in the At the same time, we will need to understand more about the characteristics of black holes than we have covered so far. It's actually quite difficult to say much about the characteristics of a black hole.

Precisely because of the event horizon, we cannot see what the inside of a black hole is like. In fact, there are only three things we can say about black holes with any degree of certainty: they have mass, charge, and angular momentum. You might be wondering how we know these things about black holes, since no light can come out of them to tell us about them. The key to these three features is that all three represent aspects of the black hole that can be felt outside the black hole's event horizon. Charging, for example, works the same way around a black hole as it does around any other charged object.

That is, if a black hole is charged, it will attract objects that have a different charge and repel objects that share its charge. Think of it as a giant magnet that pushes and pulls the universe around you. Scientists can track objects approaching a black hole, and by seeing how fast certain objects known to have charge move toward it, scientists can predict the charge of the black hole itself. Interacting with this is mass. The mass of a black hole can also be felt outside the sphere of its event horizon. In fact, he is the main creator of the event horizon in the first place.

This is because mass creates gravity and does so in a fairly linear manner, according to the same principles that can be found in Gauss's law (a theorem about electromagnetism), albeit with a gravitational analogue. Therefore, it is also possible to calculate the mass of an object by seeing how far away objects are before they start accelerating towards it and how fast they are accelerating. Although, obviously, you have to take control into account at the same time, or the results could be biased. Finally, angular momentum or spin. It is possible to detect the spin of a large mass object, and we'll delve into how in a moment.

For now, let's accept it as a given and recognize that black holes are indeed very high mass objects. There are different sizes of black holes. The smallest ones, known as micro black holes, have a mass comparable to that of our Moon, or 7.35 × 1022 kilograms. They fit all of this into a space that is only 0.2mm in diameter, which is incredible. It really gives you an idea of ​​how dense a black hole can be: something thinner than a human hair and containing the mass of the Moon. And those are just the smallest ones. Stellar black holes have a mass equal to 10 times that of our Sun and a diameter equal to 60 kilometers.

Intermediate black holes have the mass of 1,000 suns and all that mass fits into a diameter of 2,000 kilometers, which is even smaller than Earth. It is the largest black holes that really outshine us, with masses between 100,000 and 10,000,000,000 times the mass of the Sun, and sizes ranging between 0.001 and 400 AU (an astronomical unit is the distance between the Earth and the Sun) . But apart from those three characteristics, in theory there are no other differences between them. If we put two black holes in the same room and made sure they had the same mass, charge, and spin, it would be impossible to tell them apart.

However, these three features are enough to have some interesting effects on the area of ​​space outside a black hole. Traveling inside a black hole is impossible, space and time are torn apart beyond the event horizon. But we think we know some things that must exist within one. The singularity is believed to reside at the heart of a black hole. Actually, this is the black hole. When we were talking about diameters before, that was just the diameter of the event horizon. Once again, we are not sure what a black hole is really like, because light can never escape from it.

In a space that is infinitely small, there is a point where all the mass of the black hole is packed together so that it is infinitely dense. For the simplest models of black holes, those that do not rotate, it is a single point. In a rotating black hole, this is more like a small rotating ring; Otherwise, it would be difficult to define the spin of a point that has no volume. Our current physics gets very strange around such a black hole. If you follow ideal paths around this point, it becomes mathematically possible to do very strange things, like encounter your own past.

This has some disturbing implications for causality and delves into time travel paradoxes like the grandfather paradox, so it probably just shows with certainty that our ideas about singularities aren't quite right yet. Because the singularity is so small, a successful fusion of quantum theory and general relativity theory will be necessary to adequately explain what happens inside a black hole, and we haven't managed to do it yet. Perhaps one day it will turn out that singularities do not exist at all in the hearts of black holes. But this is the extent of our knowledge so far. Well, whatever is inside a black hole, it drives our engine faster than light, because, like most objects in the universe, it spins.

And oh, tour? As we move away from the center of the black hole, we pass through the event horizon with little fanfare. In reality, the event horizon cannot be detected locally; Although a person outside the black hole might be able to watch you slow to a complete stop as you travel through it, from their perspective it might appear that time is flowing normally. Normally, that is, until the universe outside the black hole runs its course in an instant because time outside the black hole travels very fast compared to you. This is the essence of relativity. In fact, the only evidence you may have that you have passed the event horizon is because of something that exists just outside it: the photon sphere.

In an area just outside the event horizon, there is a point in space where, if a photon enters it at the right angle, it will enter a perfect orbit around the black hole in the same way that the Moon perfectly orbits the Earth. This infinitely thin area is known as the photon sphere, and given the number of photons that have flown past black holes in the millions of years they have existed, it is probably full of photons. You may very well be instantly fried passing this point. However, it is just outside of here that we find the area that interests us.

The Ergosphere. This is the area around a black hole where we can most easily detect its spin. And, in this area, it is impossible for us not to move. You see, mass affects space. We see this in the curved effect of gravity on the travel of objects through that region of space. However, it might be more accurate to say that the mass "drags" the space around it. As you move through space, you bring a little bit of that space along for the ride. And when an object as massive as a black hole rotates, an effect known as frame creep occurs.

In short, the reality around the black hole begins to spin in a whirlpool that cannot be fought. Just like a real whirlpool, anything trapped inside the ergosphere spins around the black hole, because the reference frame it is in is being pulled. Kind of like how a person moves because they are standing on a moving walkway. The greater the spin of the massive object, the faster this will happen. And in the ergosphere, this can happen at a speed so fast that, at the event horizon, space is moving faster than the speed of light. It would need to travel faster than the speed of light in the opposite direction just to remain relatively still from the point of view of aexternal observer.

Which, of course, you can't do. But isn't this against the laws of physics? Doesn't Einstein say that nothing can travel faster than the speed of light? The answer is yes, but black holes have found an interesting loophole. You see, this rule only applies locally. Right where you are, in your frame of reference, nothing can go faster than the speed of light. But thanks to relativity, it is possible for reference frames to move away from each other so quickly that, from our point of view, the objects in them appear to be breaking this light barrier. But if you approached them and entered their frame of reference, they would appear to slow down and begin to obey the laws of physics again.

It's a really strange effect, but frame dragging is a real thing. It is by measuring frame drag that scientists can learn the spin of a black hole. However, according to a man named Roger Penrose, there may even be a way to exploit it. If you were to send a rocket into this section of the ergosphere, the rocket would accelerate as it became caught in the whirlpool of reality. Once it had gained enough speed, it could fire propellant in such a direction that it would exit the whirlpool again, but now traveling at a much faster speed. This method, called the Penrose Process, could hypothetically provide you with energy equivalent to about 20% of your rocket's mass.

That may not seem like much, but remember, according to Einstein's e=mc2, its 20% mass would produce energy equal to itself multiplied by 299,792,458. Squared. That's a lot of energy. So, to harness this colossal kinetic energy, all one would have to do is travel to the nearest black hole, which is approximately 3,000 light years away from us, and enter its ergosphere with a rocket capable of surviving the intense gravitational forces there. . The ideal would be to find one that was not surrounded by an accretion disk, because they reach temperatures of millions of degrees as they spin at speeds close to light and melt from solids to gas and plasma.

But you get the idea. Easy! Ok, maybe this is a little impractical for us. But the implications for faster-than-light travel that black holes demonstrate by dragging frames could offer us the key to one day truly overcoming the light barrier. Not by going faster than light ourselves, but by somehow convincing the frame of reference we are in to travel at those faster speeds, just as they do around a black hole. Of course, if this requires the energy of a black hole to achieve, we may be out of luck for now. But it's an incredible glimpse into what's possible, and scientists are already investigating the power of frame dragging for future trips.

But maybe that's a topic for another video. Either way, all of this highlights once again how our universe is actually very different than we could have ever imagined. And here's another surprising thing about black holes that you might not have known about before. Falling into a black hole is much more difficult than it seems. You might expect it to be relatively easy. After all, aren't these the best absorbers, literally the greatest sources of gravity there are? Shouldn't they be easier to fall into than anything else in the universe? You could have thought about it but, paradoxically, your intuition is wrong.

These galactic maws are one of the most difficult places in the universe to enter, so much so that, during his lifetime, Einstein believed you couldn't enter them at all. Not only that, but black holes could even eject you from them at speeds close to the speed of light. Shouldn't these objects be incredibly easy to access? Like a slide that gets steeper and steeper the steeper you go, you could expect it to speed up more and more the closer you get to the center of the black hole. However, while this is correct, it is also incorrect. You accelerate, so much so that your speed will begin to approach that of light.

However, in almost all circumstances, you will not find yourself getting close to the center of the black hole. And this isn't me talking about some strange quirk of time or relativity, but rather something that will be observable from whatever frame of reference you're looking from. Confused? Don't worry. Let me explain, through the real-world example of something called an accretion disk. Black holes are, in essence, very simple. In something known as the “hairlessness theorem,” black holes are said to lack almost any feature, like a head that, well, has nothing. The characteristics of a black hole are also usually quite simple.

They have charge, mass and spin, and that's it. As such, accretion disks are not actually a necessary part of black holes. Black holes can exist perfectly without them, sitting there, dark and unobservable in space. However, when a mass like that of an unfortunate star gets too close to the black hole's gravitational pull, the enormous forces at work can tear it apart and suck it into the center of the black hole. However, strangely enough, not all of this stuff immediately falls into the black hole's event horizon. Instead, the matter typically coalesces into a sort of flat ring that orbits the black hole outside the event horizon.

While everything eventually comes in, this process can take a long time. Some accretion disks take 100 to 1 billion years to be completely absorbed. So what is going on here? Why doesn't matter just enter the black hole? The answer is that you stumble upon a surprising principle of physics known as conservation of momentum. First described by mathematician John Wallis in 1670 and then pioneered by his contemporary Newton a decade later, the idea is this: if you have a group of objects, the motion of those objects, also known as their momentum, collectively always must remain the same. same. If a particle with momentum collides with a particle that is stationary and they bounce off each other, the total momentum of the two particles must equal the amount of the first particle alone.

No momentum can be lost. If you have a rocket on a launch pad with zero thrust, it can only generate thrust by firing propellant in the opposite direction. Once you add the amount of thrust imparted to the air by the booster on descent and the amount of thrust given by the rocket on ascent, then the upward thrust and downward thrust are equal, resulting in the same net thrust 0 as you had for a start. This is a little outside our expectations. After all, we, as human beings, often stop and start walking, apparently without obeying this law. However, if all the particles involved are evaluated, this law always holds.

You would have a hard time moving anywhere without a ground to push against. The momentum imparted to the ground should be equal to the amount of momentum imparted to you, but in the opposite direction: you just don't notice it because the ground is so much bigger than you, the amount of momentum you give it doesn't move it. . any perceptible form. But what does this have to do with falling into a black hole? Well, consider the following example, this time related to angular momentum. Imagine a dancer who has her arms extended and spins on a single point.

The particles in her hands have momentum. They move a certain distance in a certain period of time. However, they then bring their arms closer to her body. What happens? Well, suddenly they start spinning a lot faster. This is a classic example of trying to maintain momentum. You see, the momentum in the hands is still trying to travel at the same speed it was traveling at previously. However, suddenly, because it is closer to the body, it now travels a much shorter distance, but does so at the same speed. Effectively, it has to travel much less distance to complete a revolution, and as a result, it completes that revolution much faster.

This causes the dancer to spin faster when she folds her hands inward and slower when she extends them. Now imagine this on a cosmic scale. In most scenarios, matter does not fall in a perfectly straight line toward a black hole. It will almost always lose it slightly and begin to spiral towards its center when it becomes trapped in the black hole's gravity. Now it has angular momentum. As it approaches the center of the black hole, it begins to accelerate, moving at the same speed in a smaller and smaller orbit, gaining more and more angular spin as it falls into the gravity well, just like the ballerina.

Do you want to fall a little deeper? You just have to spin a little faster. However, unlike the dancer, this matter has to deal with the speed of light. Nothing in the universe can travel faster than the speed of light. This is a law discovered by Einstein. So what happens to our spinning matter as it falls further and further into the black hole? Due to the enormous forces and curvature involved, it eventually reaches a point where it can't go any faster. You have hit an obstacle. And since it can't spin any faster, it can't fall any further into the black hole.

This has several effects. For starters, as you can imagine, that creates friction. All this matter, spinning at breakneck speeds around the edge of the event horizon, begins to collide with each other. And when this happens at speeds close to the speed of light, things get very hot. The matter in the accretion disk of a black hole can reach temperatures of up to 10 million kelvin. This is enough to melt anything into hot plasma. All of these constant collisions hit the atoms involved, causing them to emit more and more energy, like squeezing a lemon. This reduces its mass.

In this way, between 10 and 40% of the mass of an atom is released in the form of energy, which is then radiated throughout the universe. For comparison, nuclear fusion (the process that takes place in the sun) converts only about 0.7% of mass into energy. Let that sink in for a moment. Consider how bright the sun is, at 0.7%. How bright can a black hole accretion disk get? The brightest disks are known as quasars and can reach brightnesses exceeding 1,000 times the total brightness of each Milky Way star combined. The good news is that, in addition, part of that momentum begins to be lost with the departure of energy.

More matter is released by imparting it to matter higher up in the accretion disk, as faster-moving particles collide with slower-moving particles just above them, giving them an extra push and slowing down the particles. lower particles. In this way, matter begins to lose its angular momentum and finally begins to fall into the black hole itself. More momentum may be lost through one of the most surprising features of quasars and black holes: their jets. We don't understand everything about these jets (how they form and what they are made of) and only a small fraction of black holes with accretion disks have them.

But current theories suggest they are caused by magnetic forces created by the rotating accretion disk, or even by the spinning power of the black hole itself, which pulls material from the accretion disk and shoots it into space. It is likely that as the accretion disk rotates, magnetic fields will form according to Ampere's law, due to all those electrically charged particles in motion. The strength and shape of these fields are such that there is only a narrow channel at the north and south poles of the black hole for the particles to escape. These magnetic fields can work similar to the serrations on a gun: funneling particles into a narrow barrel.

Particles moving at near-relativistic speeds have only one direction they can go, although we still don't really know why they do so. Perhaps they are like steam from a teapot, shot through the only gap that exists before this incredible gravitational and thermal pressure. And when they're gone, they're gone. Relativistic jets travel farther than the galaxies from which they originate and are often millions, if not billions, of light years in length. A jet with the catchy name PSO J352.4034-15.3373 (PJ352-15 for short) beams its X-rays to Earth from 12.7 billion light-years away, albeit faintly. This is because the radiation produced by such jets is highly focused in one direction.

In an effect known as the relativistic beam, or lighthouse effect, when the beam points away from us, it is much harder to see. Take, for example, the now famous galaxy M87. Here, very clearly, Hubble detects a relativistic jet. This is the one coming towards us. It is very likely that there is another plane, but we cannot see it because it is going in the opposite direction. It's worth noting that this energy doesn't come directly from the black hole; Remember, nothing can escape a black hole. Instead, matter and radiation come from the accretion disk thatsurrounds the black hole.

And again, much about these aircraft remains theoretical. We can see them, even watch them move over time, but we don't fully understand them or what causes them. Our understanding of accretion disks does not even fully explain how conservation of momentum is maintained; There's still some mystery about where all the momentum is going. But the sheer power at play is undeniable. Einstein may have been wrong: it is obviously possible to fall into a black hole. But when some black holes shoot material at near-relativistic speeds at distances spanning galaxies, well... it's evidently possible not to fall into them, too.

And once you factor in the force of matter that's millions of degrees in temperature, pushing itself toward you as it tries to shake off its own momentum... you might not want to get too close to one anyway. So, we've seen how the impressive effects of a black hole can span entire galaxies, but the question arises: how big can a black hole really get? Finding the largest black holes is not difficult, just look at the centers of large galaxies. These supermassive black holes have grown since their formation billions of years ago. More and more matter falls into them, continually increasing their mass.

The largest of these supermassive black holes may be billions of times the mass of our Sun. However, you may find it surprising to realize that some of the most massive black holes we know of are actually also the youngest. You see, when we look at distant galaxies, we're also looking back in time, and galaxies billions of light years away typically have the largest black holes. If the universe is only 13.8 billion years old and it takes light billions of years to reach us, that means the galaxy we are observing can only be a few billion years old at most from our perspective, pretty young for a galaxy However, it should surely be the case that the closer, and therefore older, supermassive black holes are more massive, since they have had a lot of extra time to consume the matter falling into them.

So what is going on here? The largest supermassive black hole we know of is known as TON 618, with an incredible mass of 66 billion solar masses. By itself, its mass is comparable to that of the Milky Way. However, TON 618 is exceptionally far away and the light it emits takes 10.8 billion years to reach us, meaning we are observing it as it was 10.8 billion years ago. This means that it can be at most 2.8 billion years old. By comparison, our own Milky Way is about 13.6 billion years old, but the supermassive black hole at the core of our galaxy, Sagittarius A*, is only 4 million solar masses.

The Andromeda galaxy's supermassive black hole, although larger, is still only 200 million solar masses. One of the big factors to consider here is the difficulty of detecting and measuring black holes. This is still a really new field of research, as technology has only allowed us to begin observing black holes in the last few decades. Even then, we can often only observe the area around black holes, that is, before the Event Horizon Telescope appeared. But even that telescope takes years to image a single black hole, so our overall understanding remains quite limited. In fact, most of the distant black holes we know about can only be seen because they are quasars.

TON 618 is a quasar. Matter is pouring into the black hole's accretion disk at an incredible rate and because of this, it has erupted into a quasar. Quasars can only maintain themselves as long as matter falls into them; Otherwise, they will become dark black holes again. It is difficult to fully understand the physics of the accretion disk, but the friction here is thought to be so great that a quasar's accretion disk alone can produce thousands of times more light than entire galaxies combined. TON 618 produces as much light as 140 trillion suns, completely eclipsing the galaxy in which it resides, to the point that we can't even see it from our perspective.

However, because quasars are the brightest objects that exist, they can be seen from very far away. So one of the reasons the largest black holes are so far away is due to something known as Malmquist bias. This is where brighter objects further away appear more abundant, when in reality we simply cannot see the fainter objects at that distance, implying that there may be an argument that the largest supermassive black holes are actually distributed fairly evenly throughout the universe. If a galaxy has a very large black hole but it is not a quasar, it means that we will not see it after a certain distance because a galaxy is much fainter than a quasar.

Another reason we don't see the largest black holes near us is due to the nature of the universe itself shortly after the Big Bang. As you know, the universe is constantly expanding and, during its beginnings, matter was much closer together. Quasars were more common back then because they needed extreme amounts of matter to fall into them to emit light, and there was much more gas during the early stages of the universe. Not only has the universe expanded, but over time the gas has expanded. turns into stars. Some of the largest types of stars eventually become neutron stars and black holes, meaning they can never be recycled back into gas.

Less available gas means less gas will fall into a supermassive black hole. Actually, one of the theories about the fate of the universe is based on this, called the Big Freeze, where after a few billion years, all the gas in the universe eventually turns into black holes. Even now, we see some galaxies where their gas has been completely used up, meaning new stars cannot form. These are called elliptical galaxies. Spiral galaxies still have gas and dust structures and can therefore still produce new stars. Interestingly, most of the largest supermassive black holes appear to be in elliptical galaxies, where there is no gas left.

Gas needs to lose angular momentum to fall into the galaxy's central supermassive black hole, and if that were to happen, then the supermassive black hole would likely be much larger due to all the matter falling. With elliptical galaxies this has already happened, while with spiral galaxies it has not happened to the same extent. One of the triggers for the loss of angular momentum of the gas could be the gravitational influence of nearby galaxies, or even collisions with other galaxies. Additionally, there is less gas available in the universe now than during the early universe, so the growth of black holes probably occurred rapidly then, but has slowed down now.

This could be the reason why there are no quasars within 500 million light years of us. As the universe ages and things become less chaotic and more spread out, the number of active quasars has decreased. Which means that the only quasars we see, some of which are the largest black holes we know of, are ones that emerged a long time ago. So why are the largest supermassive black holes usually the youngest? Well, although it may seem like that, it may not actually be like that at all. We can measure distant bright quasars simply because we can see them.

The oldest and closest black holes may also be large, but due to Malmquist bias, we haven't found them yet. As studies continue and technology improves, we will begin to have a more complete picture of the universe around us. There we have it, almost everything you could want to know about black holes. Is there more to discover about them? Almost certainly. But one thing is for sure: they have completely distorted my concept of what is normal in this universe of ours. If you find value in this video, be sure to subscribe and like it, and even share it with someone who might enjoy it.

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