What would a journey to a black hole be like?

Right now, twenty-six thousand light-years from your chair, nestled at the very center of our galaxy, lies something so monstrous, not even light, the fastest thing in the universe, can escape from it. Sagittarius A*, a stellar cluster, a supermassive black hole with a mass of four million suns. It doesn't glow, it doesn't make noise; it simply sits there in absolute silence, slowly devouring anything that comes too close. Stars, gas, dust, time. Everything vanishes beyond an invisible boundary from which there is no return. But what if we had a ship? Not just a ship, but a machine capable of surviving this journey—or at least transmitting data before ceasing to exist. What would we see? What would we feel? And most importantly, what would happen to our body, to our time, and to reality itself, as we approach the point where the laws of physics cease to function. Today we will embark on this journey, step by step, from a safe distance to the very edge of the event horizon and beyond. Get ready, because what physics predicts will turn out stranger than any science fiction. Before setting off on our journey, let's first understand what a black hole actually is. Forget the movie image, the giant vortex in space sucking everything in. A black hole is neither a hole nor a funnel. It is an object. More precisely, an unimaginably dense object that has compressed its entire mass into a point of infinitely small size. which physicists call a singularity. Space-time is curved so intensely around this point, At a certain distance, the required escape velocity exceeds the speed of light. This distance is called the event horizon, not a physical surface. and the mathematical boundary beyond which information ceases to be accessible to an external observer. Everything that crosses the event horizon remains inside forever. Black holes come in different types. Stellar black holes are the remnants of massive stars that collapsed under their own gravity. have masses ranging from several to several tens of solar masses. Their event horizon is several dozen kilometers in diameter. Supermassive black holes, such as Sagittarius A* at the center of the Milky Way or M87, the central star in the Virgo galaxy, contains millions to billions of solar masses. The event horizon of the M87 black hole is larger than our entire Solar System. It was the M87 black hole that became the first black hole to be directly imaged. the image of which was obtained in 2019 by the Event Horizon Telescope project – A dark silhouette against the glowing disk of gas and plasma. To obtain this image, eight radio telescopes were required to be combined. scattered across the planet, from Hawaii to the South Pole a single virtual telescope the size of Earth. The data array collected during one night of observation amounted to 5 petabytes. So much that it would be faster to transfer them on hard drives by airplane than to send them over the internet. Result – a blurred orange ring around a black spot It became one of the most important images in the history of science. For the first time, humanity saw what by definition was invisible. In 2022, the same project received an image of the A-Star archer. a black hole at the center of our own galaxy. It turned out to be significantly smaller than the M87 star, but no less impressive. For our mental journey, we will choose a supermassive black hole. And that is why. For small black holes, tidal forces near the event horizon are monstrous. The difference in gravitational attraction between your feet and your head would be so immense, what would have literally torn you apart long before crossing the horizon. Physicists call this process spaghettification, and it's as terrifying as it sounds. But the event horizon of supermassive black holes is so large, The tidal forces at its boundary are relatively weak. You could cross the event horizon of the Scorpius A-Star without even noticing. At least, at first. It is precisely this that makes supermassive black holes ideal candidates for our thought experiment. So, we're on the ship. Engines are running, coordinates are set. We are beginning the approach. Stage one. A distant approach. Distance – a few light-years from the black hole. At this distance, the black hole is completely invisible; it does not emit light. But you notice her presence through indirect signs. The stars against the backdrop of a black hole are slightly shifted. Their light is bent by gravity as it passes near an invisible object. This is called gravitational lensing. A black hole acts like a giant lens, bending light rays around itself. If you were looking directly at a black hole, you would see a characteristic effect – an Einstein ring. The light from distant stars bending around a black hole from all sides and converging into a glowing ring. This spectacle would be mesmerizing. A thin, glowing hoop in absolute emptiness. At this distance, you are still completely safe. The gravity of a black hole is felt. But it is no stronger than the gravitational pull of an ordinary star. Your watch is running normally. Your body feels great. The only thing unusual is the sky. It starts to look a bit strange. The stars behind you, in the direction from which you came, appear slightly bluer. Stars ahead, in the direction of the black hole, slightly redder. That is the Doppler effect. As you gain speed falling through the gravitational field, The light ahead is narrowing, while the light behind is stretching out. The effect is barely noticeable for now, but it will soon become significantly more dramatic. Stage two – accretion disk. A few hundred event horizon radii. If our black hole is active, meaning there is matter falling into it around it, Before you unfolds one of the most magnificent spectacles in the universe. An accretion disk – a flat ring composed of gas, dust, and plasma, orbiting a black hole at near-light speed. Friction between the layers of the disk heats the material to millions of degrees, and it begins to emit in the X-ray and gamma-ray ranges. If your eyes could see across the entire electromagnetic spectrum, The accretion disk would shine brighter than a billion suns. A remarkable fact – accretion disks of black holes – the most efficient energy sources in the known universe When matter falls into a black hole, It converts up to 40% of its mass into energy. For comparison, nuclear fusion in the Sun's core converts less than 1%. That is why quasars, the cores of distant galaxies, at the center of which is an actively absorbing substance of supermassive black holes shine brighter than all the stars of their home galaxy combined. Some quasars emit as much energy as a trillion suns. And all of this is from the realm of space, not exceeding the size of our Solar System. Relativistic jets emerge from the poles of many active black holes – plasma streams accelerated to 99% of the speed of light and stretching for thousands of light-years. The mechanism of jet formation is not fully understood. but it is considered that magnetic fields play a key role, spun by a rotating accretion disk. If our ship were to be in the path of the jet stream, That would be instantaneous annihilation. A stream of particles with energy exceeding all others What can terrestrial accelerators generate? Yet even in visible light, the spectacle is overwhelming. The disc does not look like you expect. Due to the monstrous curvature of spacetime Light from the far side of the disk bends around the black hole. and becomes visible from above. At the same time, the light from the lower part of the disk bends around it from below. As a result, you see not a flat disk, and something resembling a hat—a glowing stripe, Wrapped around the dark sphere from several sides at the same time. It was precisely this effect that was calculated by physicist Kip Thorne and brilliantly visualized in Christopher Nolan's film Interstellar. The visualization of the Gorgon in this film – One of the most scientifically accurate depictions of a black hole in the history of cinema. There is one more detail that makes the disk's appearance asymmetrical. The part of the disk moving toward you it appears significantly brighter than the part moving away from you. This is relativistic amplification. Light emitted by matter traveling toward you at near-light speed, Contracts and intensifies. The opposite side, on the contrary, fades. The disc looks as if one half of it is burning with white fire. The other one barely smolders. This effect is called relativistic beaming. And it transforms the symmetrical structure into an asymmetrical, almost living spectacle. At this distance, the first noticeable relativistic effects begin to appear. If you could contact someone on Earth, or with someone who remained far away from the black hole You would have noticed something strange. Their clocks run a bit faster than yours. Or, from their point of view, your clocks have slowed down. This is gravitational time dilation. A direct consequence of Einstein's general theory of relativity. The deeper you penetrate into the gravitational field, The slower time passes for you compared to an external observer. The difference is currently minimal—fractions of a percent. But it will grow exponentially. Stage three — the photon sphere. Distance — one and a half Schwarzschild radii from the center of the black hole. The Schwarzschild radius is essentially the radius of the event horizon for a non-rotating black hole. For a black hole with a mass of 10 solar masses, it is approximately 30 kilometers. For the Archer constellation, approximately 12 million kilometers. About 17 times the distance from Earth to the Sun. The photon sphere is one of the most exotic regions around a black hole. At this distance, gravity is so strong, Photons, the particles of light, can travel along circular orbits around a black hole. Light literally orbits around her like a satellite around Earth. If you were stuck on the photon sphere and looked straight ahead, You would see your own nape. Your own light, bent around a black hole, would return to you. Theoretically, you might see several copies of yourself. The light can make several turns before deviating. Of course, it's impossible to get stuck on a photon sphere. The orbit is unstable here. Even the slightest disturbance will send you either outward or inward toward the event horizon. But the very concept of a place where light moves in a circle, demonstrates how extremely warped spacetime is near a black hole. At this distance, the sky looks utterly alien. The black hole before you now occupies a significant portion of the view. Not as an object, but as a region of absolute darkness, surrounded by a thin rim of distorted light. The stars behind you are still visible, but their images are distorted beyond recognition. They are stretched, blurred, and shifted. The entire universe, if you could turn around would have looked like a glowing, contracting ring above you, As if you were looking up from the bottom of a well, with the stars gathered at its rim. Time dilation due to gravity is already significant here. Each hour on your clock corresponds to several hours for a distant observer. If you spent a day here and somehow returned, Significantly more time would have passed on Earth. Remember the movie Interstellar. One hour on the planet near Gargantua equaled seven years on the ship. This is not science fiction; it is the mathematics of general relativity. Stage 4. Approaching the event horizon. Distance – in Schwarzschild radii units. You're falling. The engines won't help. To stop, you would need infinite energy. The fabric of spacetime around you is curved so greatly, the very notion of "outward" begins to lose meaning. All directions, including spatial ones, gradually unfold toward the singularity. You haven't crossed the horizon yet, but escaping is practically impossible. To an outside observer, the one watching you from a safe distance Something paradoxical is happening. He sees you slowing down. Your ship appears to slow down more and more as it approaches the event horizon. Your image is turning red. The light you emit gets stretched by gravity, shifting toward the red, and then into the infrared part of the spectrum. From his point of view, you will never cross the event horizon. You will freeze at its boundary, gradually fading until you become invisible. For him, your fall into the black hole lasts forever. This is neither an illusion nor a trick of the eye. This is a fundamental property of spacetime. Time near the event horizon flows infinitely more slowly compared to a distant observer. If you could hover just a few centimeters above the event horizon and spend one minute there, then somehow return Thousands, millions, or even billions of years could have passed on Earth. depending on how close you were A black hole is a time machine that works only in one direction – into the future. But for you, it's an entirely different story. Stage five. Crossing the event horizon. And here is the moment we have been waiting for. Event horizon. The point of no return. A point beyond which not even light can escape. What do you feel when crossing it? Nothing. Absolutely nothing. This is probably the most counterintuitive fact about black holes. The event horizon is not a wall, not a membrane, not a force field. It is a mathematical boundary, invisible and imperceptible to the one who crosses it. Einstein's equivalence principle states that A freely falling observer cannot distinguish between gravity and its absence. You are falling, and locally, the spacetime around you appears normal. And no detector will register the moment of intersection. You will know that you have crossed the horizon only by one sign – You can no longer send a signal outward. But since the signal travels at the speed of light, and you are slower, You won't even be able to verify it in real time. But here we encounter one of the greatest unresolved paradoxes in theoretical physics – the black hole information paradox In 1974, Stephen Hawking demonstrated that black holes are not absolutely black. They slowly evaporate, emitting what is known as Hawking radiation. This is a quantum effect. Particle-antiparticle pairs are born from the vacuum at the event horizon. One of them flies outward, and the other falls inward. A black hole loses mass and, ultimately, After an inconceivably long time, it completely evaporates. But where does the information about everything that fell into it go? Quantum mechanics asserts that information cannot be destroyed. General relativity states that Everything beyond the event horizon is forever cut off from the outside world. These two statements contradict each other. Resolving this paradox is one of the main unsolved questions in modern physics. Perhaps answering it will require a completely new theory—quantum gravity. which will unify quantum mechanics and general relativity. Stage 6. Inside the black hole. You've crossed the horizon. You're inside. What's next? Here, physics truly becomes strange. So much so that our language and our intuitive notions of space and time cease to function. Inside a black hole, space and time exchange roles. This is not a metaphor; it is a mathematical fact. the next solution of the Einstein equation. Outside a black hole, you can move in any direction in space, but only forward in time. Inside a black hole, the radial coordinate is the distance to the singularity. becomes timelike. This means that moving toward the singularity is equally inevitable. How to move forward in time. A singularity is not a place in space, but a moment in the future. You cannot avoid it any more than you can avoid tomorrow. All paths, all directions, all trajectories lead to her. As one approaches the singularity, tidal forces increase. For a supermassive black hole, they were weak at the event horizon. But now, closer to the center, they become monstrous. The difference in gravitational attraction between your head and your feet, even if the distance between them is only one and a half meters, begins to grow exponentially. Your body stretches vertically and compresses horizontally. This is spaghettiification—the process by which any object stretches into an infinitely thin thread. To grasp the magnitude of these forces, imagine You are standing on the surface of the Earth, and gravity pulls your feet slightly stronger than your head. The difference is approximately one ten-millionth of the total force. You don't feel it. A similar difference near the singularity of a black hole can exceed the strength that binds atoms in your body by trillions of times. At first, you will feel a slight uncomfortable stretching sensation, As if someone is pulling you by the feet and the head at the same time. Then – an intensifying pain. Then – muscle, tendon, and bone ruptures. Then — molecules, atoms. Ultimately, even subatomic particles will be torn apart by tidal forces. Everything you are will turn into a stream of elementary particles falling toward the singularity. The entire process from the first sensation of discomfort to complete destruction would have taken, probably, a fraction of a second by your own clocks. But since time behaves unpredictably inside a black hole, Even this statement is merely an approximate estimate. What is singularity? It is the point where the density of matter and the curvature of spacetime tend toward infinity. According to the general theory of relativity, A singularity is a point where volume equals zero and density is infinite. But most physicists consider this not to be a description of reality. and a signal that the theory stops working. In physics, infinities usually indicate that we are using the wrong model. No one knows what is actually happening at the singularity. This is terra incognita for modern science. Perhaps quantum effects prevent compression to infinite density. Perhaps the singularity is not a point, but some kind of quantum structure. Some theories suggest that a singularity might be a portal. a transition into another region of space-time, into another universe. But this remains speculation. There is another type of black hole that makes the story even more interesting. A rotating black hole described by the Kerr solution. Most real black holes rotate because what the stars from which they formed were rotating. In a rotating black hole, the singularity has the form of a ring rather than a point. And mathematics allows for the possibility of passing through this ring. without colliding with infinite density. Where does this ring lead? The equations predict an exit into another region of spacetime. Perhaps another universe or another point in our own. This is known as the Einstein-Rosen bridge or wormhole. However, most physicists view this possibility skeptically. The internal structure of a real rotating black hole, Probably unstable and does not allow passage. Let us momentarily step away from physics and talk about scales. Black holes are not an exotic rarity; they are everywhere. In our galaxy, according to astronomers' estimates, There are between 100 million and one billion stellar black holes. Practically every major galaxy has a supermassive black hole at its center. The recently discovered black hole TON-618 has a mass of 66 billion solar masses. It is one of the largest known. Its event horizon is so vast, what would fit inside it is our entire solar system. Several times. Black holes form galaxies, regulate star formation and may possibly play a key role in the evolution of the entire universe. And now we have a way to hear them. In 2015, the LIGO detectors gravitational waves were detected for the first time – ripples of spacetime, predicted by Einstein exactly 100 years ago. The source of the signal turned out to be collision of two black holes each with a mass of about 30 solar masses occurred more than a billion years ago. For a fraction of a second, they merged. releasing energy, equivalent to three solar masses in the form of gravitational waves, that swept across the universe and forced the detectors on Earth shift by a distance a thousand times smaller than the diameter of a proton. Since then, dozens of similar events have been recorded. We live in an era when, for the first time in history humanity can not only see the universe, and even hear her. And the voice we hear most often – This is the voice of colliding black holes. And finally. Black holes teach us how little we know. Every aspect of our journey – gravitational time dilation spaghettiification, information paradox singularity This is a window into fundamental questions. for which we currently have no answers. What is space and time At the deepest level? Can information be destroyed? Are there other universes? Black holes – These are not just exotic objects. Somewhere far away in space. These are laboratories, in which nature conducts experiments within the limits of possibility Experiments, the results of which we have only just begun to decipher. They cast doubt on our understanding of space, time, causality and of reality itself. And perhaps precisely in this lies in their main significance. Black holes show us, Where does our knowledge end? And where does the territory begin? which has yet to be opened. If you really undertook this journey, from a distant approach to singularity, Would you walk the path? from a familiar physics of everyday life beyond the bounds of human understanding. You would have seen, How does space turn into time? how light moves in a circle how the entire universe is contracting a glowing ring above your head. Would you have survived, Let it be for a few moments, experience inaccessible to any living being in history. And at the last moment, before how tidal forces They will tear apart every atom of your body, you might have seen something what no theory can predict What lies hidden Beyond infinity. Write in the comments, Which stage of the journey What impressed you the most. And subscribe to the channel, because the universe is full of objects, which are even stranger than black holes. See you!