What does falling into a black hole look like? Black holes. your point of view

Artist's interpretation of how a star crosses the event horizon of a central supermassive black hole

A black hole is characterized by incredibly strong gravity, not even emitting light. The event horizon is concentrated around it. It is enough to cross this "line" and you are doomed. Everyone knows about this, but the existence of such “lines” has not been proven.

So the scientists decided to conduct an experiment. It is believed that supermassive black holes reside in the centers of all large galaxies. But there is an opinion that there is also another object. This is an unusual supermassive something that managed to dodge collapse and singularity. It also has an event horizon around it.

If the singularity has no surface area, then the object has it solid. Therefore, the star will not fall into the black hole, but will break on the surface.

It is a huge massive sphere at the galactic center. We see a star crash into a solid surface and scatter debris

To reveal the authenticity of the theory, scientists have come up with a new test. The point is to define what a solid surface is. It would help to solve the problem with the event horizon.

To begin with, they found that when an object hits a solid surface, the stellar gas will envelop it and shine for several months or years. The telescope should pick it up. When the scientists realized what needed to be found, they confirmed their arguments.

They estimated the speed at which stars fall into black holes. For this, only the most massive ones were considered, whose mass exceeded the solar mass by 100 million times. It turned out that there are about a million such objects at a distance of several billion years from us.

Then I had to look through the archival data of the 1.8-meter Pan-STARRS telescope, which had been exploring the northern hemisphere for 3.5 years for a "temporary glow". If the assumption is correct, then taking into account all the data, the telescope should have identified 9-10 such events.

And... he didn't find anything.

It turns out that all black holes must have an event horizon. So Einstein was right again. Now the team is trying to improve the test and test it on the 8.4-meter Large Survey Telescope (Large Synoptic Survey Telescope), which is more sensitive.

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A black hole is a region of space that has such an attraction that even light cannot escape it. The idea of ​​the existence of such objects appeared at the end of the 18th century, when the English naturalist John Mitchell suggested that if the size of a star is very small and the mass is very large, then it will not shine, because its attraction simply will not let the light escape (Mitchell imagined itself light consisting of particles).

In modern science, the existence of black holes is predicted by the theory of relativity. Gravity in accordance with this theory is visually as follows: imagine a fabric, or rather a sheet of rubber, on which stones are placed. The stones push it harder or weaker depending on their weight, and the lighter ones roll to where the heavier ones pushed the hole deeper. Therefore, the planets "attract" the satellites, the Sun "attracts" the planets, and so on.

Beware of black holes and waterfalls

Using this metaphor, Stephen Hawking explains black holes like this: imagine that we put a very heavy and compact stone on rubber, it pushes a bottomless pit into which the substance falls irrevocably.

The boundary of a black hole is called the event horizon, beyond this horizon the speed with which you need to move in order to escape from the black hole must exceed the speed of light - an impossible task. You can imagine this as a fall on a boat into a waterfall: the closer to the waterfall, the harder you need to row so that it doesn’t drag out, but from some point, no matter how hard you try, you won’t be able to escape, you fall, but in the case of a black hole at the bottom you are not waiting for sharp stones, but a mysterious singularity.

In the region of the singularity, the density of matter becomes infinite. It is said that a tunnel to another universe may even form. But these are all rumors, and no one knows what is really going on there.

All this sounds strange and mysterious, but the fact that black holes exist, astrophysicists: for example, the long-awaited discovery generated by the collision of two black holes, is a weighty confirmation of their existence.

Where do black holes come from

Stellar-mass black holes are formed from stars with a mass 3-5 times greater than the sun (therefore, our Sun will not become a black hole, it will turn into a white dwarf in billions of years). The "fuel" for thermonuclear reactions in stars is not infinite, and when it runs out, the star "collapses" and bursts into a supernova.

But where supermassive black holes come from is unknown. There are only assumptions on this score, such as the collapse of massive clouds of gas in the early stages of galaxy formation, the growth of stellar-mass black holes due to the absorption of matter, or the merging of many such holes into one supermassive one. There is no shortage of assumptions, but observations are more difficult.

How to see a black hole

It is impossible to see the black hole itself, as its name hints at, but the matter falling into it is possible. At the centers of many galaxies are black holes millions larger than the sun. They attract dust, gas and stars. This material forms an accretion disk around the black hole. In it, matter swirls like in a funnel before falling into a black hole, and due to friction it heats up, due to which it begins to glow brightly across the entire spectrum. When matter falls into a black hole, the radiation pressure and the influence of the magnetic field near the boundary of the black hole throw part of the matter away from it.

The supermassive black hole at the center of our Galaxy is called Sagittarius A*. The phrase “our Galaxy” sounds somehow homely, as if it is within easy reach of the center, but in fact the black hole is 25 thousand light-years away from us, its mass is 4 million times greater than the sun.

It is very difficult to see it at such a distance - it's like trying to see a tennis ball on the moon, and the sharpness of "vision" necessary for this is available only to radio telescopes thanks to a technique that allows you to combine telescopes in different parts of the globe into one huge virtual telescope. Thus, the Event Horizon Telescope project will unite observations of telescopes in the USA, Spain, Mexico, Chile and even in Antarctica.

The second object to observe is the black hole at the center of the M 87 galaxy. It is about 6 million times more massive than the Sun, but it is also much further away - 53 million light-years from us.

What does a black hole look like

The results of the observations will not be published until next year, but for now, in order to roughly imagine what telescopes can see, you can admire the black hole in the movie Interstellar, the creators of which tried to make the picture as scientifically correct as possible.

The correctness of this picture is that the accretion disk behind the black hole does not look like the rings of Saturn, but peeks out from behind the black hole, because its strong gravitational field distorts the path that the accretion disk radiation travels. However, there is a difference from Interstellar: on the one hand, the accretion disk should look brighter due to its rotation.

As a result, the image should look similar to the picture that astrophysicist Jean-Pierre Luminet modeled in 1978 on an IBM 7040 computer that worked on punched cards, and drew it by hand for a magazine article Astronomy and Astrophysics.

Black holes are perhaps the most mysterious objects in the universe. They are so dense that the force of gravity does not allow anything, not even light, to escape the black hole. Physicists have discovered many black holes, from small to supermassive, millions or billions of solar masses. An important property of the event horizon - that light cannot cross it - creates a boundary in space: once you cross it, you are doomed to find yourself in a singularity. But what do you see when you fall into a black hole? Will the light go out or stay? Physicists know the answer, and you'll like it.

At the center of our own galaxy, we have seen stars moving around a central point of mass of 4 million solar masses, emitting no light. This object, Sagittarius A*, is a clear black hole candidate that we can determine directly by measuring the stars in its orbit.

But there are some very strange things that happen when you get close to a black hole's horizon, and they get even weirder as you cross it. There is a reason why once you cross this invisible barrier, you will never be able to leave it. And it doesn't matter what class of black hole sucked you in, what spaceship is trying to take you out of there, or something else. General relativity is serious stuff, especially when it comes to black holes. The reason has to do with Einstein's greatest achievement: it has to do with HOW a black hole warps spacetime.

When you are very far from the black hole, the fabric of space is less curved. In fact, when you are very far away from a black hole, its gravity is indistinguishable from any other mass, be it a neutron star, an ordinary star, or just a diffuse cloud of gas. Space-time can be curved, but all you can tell from afar is the presence of mass, without knowing the distribution of that mass. But if you look with your own eyes, then instead of a cloud of gas, a star or a neutron star, there will be a completely black sphere in the center that does not emit any light.

This spherical region, known as the event horizon, is not something physical, but rather a region of space of a certain size from which no light can escape. One might assume that from afar, the size of a black hole seems to be what it really is. In other words, if you get close to a black hole, it will look like a completely black hole against the background of space, along the boundaries of which light is distorted.

For an Earth-mass black hole, this sphere would be tiny: on the order of 1 centimeter in radius; and for a black hole with the mass of the Sun, this sphere will be about 3 kilometers in radius. If you scale the mass (and size) to a supermassive black hole - like the one at the center of our galaxy - you get the size of a planetary orbit or a giant red star like Betelgeuse.

What happens when you get close and eventually fall into a black hole?

From a distance, the geometry you see will match your expectations and calculations. But as you move forward in your perfectly designed and indestructible spacecraft, you will begin to notice something strange as you approach the black hole. If you divide the distance between you and the star in half, the angular size of the star will appear twice as large. If you shorten the distance to a quarter, it will be four times as large. But black holes are different.

Unlike all the other objects you're used to, which seem to get bigger the closer you get, a black hole grows in size much faster thanks to the incredible curvature of space.

From our perspective on Earth, a black hole at the galactic center would appear tiny, with a radius measured in microarc seconds. But compared to the naive radius you calculate in GR, it will appear 150% larger due to the curvature of space. If you get close to it, by the time the event horizon is the size of a full moon in the sky, it will be four times that. The reason, of course, is that spacetime gets more and more curved as you get closer to the black hole.

Conversely, the observable area of ​​a black hole grows larger and larger; by the time you are within a few Schwarzschild radii of it, the black hole will have grown to such a size that it obscures almost the entire forward view of the ship. Ordinary geometric objects do not behave this way.

As you approach the innermost stable circular orbit - which is 150% of the radius of the event horizon - you will notice that the forward view on your ship will turn completely black. As soon as you cross this exactly, even behind you everything will begin to sink into darkness. Again, this has to do with how the paths of light from different points move through this highly curved space-time.

At this point, if you haven't crossed the event horizon, you can still exit. If you apply enough acceleration away from the event horizon, you can escape its gravity and return to a safe space-time away from the black hole. Your gravity sensors will tell you where the downward gradient towards the center changes to a flatness where starlight can be seen.

But if you keep falling towards the event horizon, you will eventually see starlight shrink to a tiny dot behind you, changing color to blue due to gravitational blueshift. At the last moment you cross the event horizon, this dot will turn red, white, and then blue as the cosmic microwave and radio wave backgrounds shift into the visible spectrum.

And then... there will be darkness. Nothing. From within the event horizon, no light from the outer universe can reach your ship. Now you will remember the powerful engines of your ship and think about how you could use them to escape from this trap. You will remember in which direction the singularity lay, and try to determine the gravitational gradient towards it. This is provided that there is no other matter or light behind you or in front of you.

What is surprising, even if a lot of light gets beyond the event horizon with you - you will see "half" of the visible Universe - there will also be gravitational sensors on board with you. And once you cross the event horizon, with or without light, something strange happens.

Your sensors will tell you that the gravitational gradient that goes towards the singularity will be everywhere, in all directions. Even in the direction opposite to the singularity.

How is this possible?

And like this, because you are beyond the event horizon, right in it. Any ray of light you now emit will go in the direction of the singularity; you're too deep inside the black hole for it to go anywhere else.

How long does it take after crossing the horizon in a supermassive black hole to be at its center? Believe it or not, even though the event horizon might be a light-hour in diameter in our frame of reference, it only takes about 20 seconds to reach the singularity. Strongly curved space is a terrible thing.

Worst of all, any acceleration will bring you closer to the singularity even faster. It is not possible to increase the survival time at this stage. The singularity exists in all directions, wherever you look. Resistance is futile.

Jan 31, 2018 Gennady

Image copyright Thinkstock

Perhaps you think that a person who has fallen into a black hole is waiting for instant death. In reality, his fate may turn out to be much more surprising, the correspondent says.

What will happen to you if you fall inside a black hole? Maybe you think that you will be crushed - or, conversely, torn to shreds? But in reality, everything is much stranger.

The moment you fall into the black hole, reality will split in two. In one reality, you will be instantly incinerated, in the other, you will dive deep into the black hole alive and unharmed.

Inside a black hole, the laws of physics familiar to us do not apply. According to Albert Einstein, gravity bends space. Thus, in the presence of an object of sufficient density, the space-time continuum around it can be deformed so much that a hole is formed in reality itself.

A massive star that has used up all its fuel can turn into exactly the type of superdense matter that is necessary for the emergence of such a curved section of the universe. A star collapsing under its own weight drags along the space-time continuum around it. The gravitational field becomes so strong that even light can no longer escape from it. As a result, the area in which the star was previously located becomes absolutely black - this is the black hole.

Image copyright Thinkstock Image caption No one really knows what's going on inside a black hole.

The outer surface of a black hole is called the event horizon. This is a spherical boundary at which a balance is reached between the strength of the gravitational field and the efforts of light trying to escape the black hole. If you cross the event horizon, it will be impossible to escape.

The event horizon radiates energy. Due to quantum effects, streams of hot particles radiate into the Universe arise on it. This phenomenon is called Hawking radiation - in honor of the British theoretical physicist Stephen Hawking who described it. Despite the fact that matter cannot escape the event horizon, the black hole, nevertheless, "evaporates" - over time, it will finally lose its mass and disappear.

As we move deeper into the black hole, space-time continues to curve and becomes infinitely curved at the center. This point is known as the gravitational singularity. Space and time cease to have any meaning in it, and all the laws of physics known to us, for the description of which these two concepts are necessary, no longer apply.

No one knows what exactly awaits a person who has fallen into the center of a black hole. Another universe? Oblivion? The back wall of a bookcase, like in the American sci-fi movie "Interstellar"? It's a mystery.

Let's reason - using your example - about what happens if you accidentally fall into a black hole. In this experiment, you will be accompanied by an external observer - let's call him Anna. So Anna, at a safe distance, watches in horror as you approach the edge of the black hole. From her point of view, events will develop in a very strange way.

As you get closer to the event horizon, Anna will see you stretch in length and narrow in width, as if she is looking at you through a giant magnifying glass. In addition, the closer you fly to the event horizon, the more Anna will feel that your speed is dropping.

Image copyright Thinkstock Image caption At the center of a black hole, space is infinitely curved.

You won't be able to yell at Anna (since no sound is transmitted in vacuum), but you can try to signal her in Morse code using your iPhone's flashlight. However, your signals will reach it at increasing intervals, and the frequency of the light emitted by the flashlight will shift towards the red (long wavelength) part of the spectrum. Here's how it will look: "Order, in order of documents, in order of ...".

When you reach the event horizon, from Anna's point of view, you will freeze in place, as if someone paused the playback. You will remain motionless, stretched across the surface of the event horizon, and an ever-increasing heat will begin to take over you.

From Anna's point of view, you will be slowly killed by the stretching of space, the stoppage of time, and the heat of Hawking's radiation. Before you cross the event horizon and deep into the depths of the black hole, you will be left with ashes.

But do not rush to order a memorial service - let's forget about Anna for a while and look at this terrible scene from your point of view. And from your point of view, something even stranger will happen, that is, absolutely nothing special.

You fly straight to one of the most sinister points in the universe without experiencing the slightest shake - not to mention the stretching of space, time dilation or the heat of radiation. This is because you are in free fall and therefore do not feel your own weight - this is what Einstein called the "best idea" of his life.

Indeed, the event horizon is not a brick wall in space, but a phenomenon conditioned by the point of view of the observer. An observer who remains outside the black hole cannot see inside through the event horizon, but that is his problem, not yours. From your point of view, there is no horizon.

If the dimensions of our black hole were smaller, you would really run into a problem - gravity would act on your body unevenly, and you would be pulled into pasta. But luckily for you, this black hole is large - millions of times more massive than the Sun, so the gravitational force is weak enough to be negligible.

Image copyright Thinkstock Image caption You can't go back and get out of a black hole, just like none of us can travel back in time.

Inside a sufficiently large black hole, you can even live the rest of your life quite normally until you die in a gravitational singularity.

You may ask, how normal can a person's life be, against their will, being pulled into a hole in the space-time continuum with no chance of ever getting out?

But if you think about it, we all know this feeling - only in relation to time, and not to space. Time only goes forward and never back, and it really drags us along against our will, leaving us no chance to return to the past.

This is not just an analogy. Black holes bend the space-time continuum to such an extent that inside the event horizon, time and space are reversed. In a sense, it's not space that pulls you to the singularity, but time. You can't go back and get out of a black hole, just like none of us can travel into the past.

Perhaps now you are wondering what is wrong with Anna. You fly into the empty space of a black hole and you are all right, and she mourns your death, claiming that you were incinerated by Hawking radiation from the outside of the event horizon. Is she hallucinating?

In fact, Anna's statement is absolutely correct. From her point of view, you are indeed fried on the event horizon. And it's not an illusion. Anna can even collect your ashes and send them to your family.

Image copyright Thinkstock Image caption The event horizon is not a brick wall, it is permeable

The fact is that, according to the laws of quantum physics, from Anna's point of view, you cannot cross the event horizon and must remain on the outside of the black hole, since information is never irretrievably lost. Every bit of information that is responsible for your existence must remain on the outer surface of the event horizon - otherwise, from the point of view of Anna, the laws of physics will be violated.

On the other hand, the laws of physics also require that you fly through the event horizon alive and unharmed, without encountering hot particles or any other unusual phenomena on your way. Otherwise, the general theory of relativity will be violated.

So the laws of physics want you to be both outside the black hole (as a pile of ash) and inside it (safe and sound) at the same time. And one more important point: according to the general principles of quantum mechanics, information cannot be cloned. You need to be in two places at the same time, but only in one instance.

Physicists call such a paradoxical phenomenon the term "disappearance of information in a black hole". Fortunately, in the 1990s scientists managed to resolve this paradox.

American physicist Leonard Susskind realized that there really is no paradox, since no one will see your cloning. Anna will watch one of your specimens, and you will watch the other. You and Anna will never meet again and you will not be able to compare observations. And there is no third observer who could watch you from both outside and inside the black hole at the same time. Thus, the laws of physics are not violated.

Unless you want to know which of your instances is real and which is not. Are you really alive or dead?

Image copyright Thinkstock Image caption Will the person fly through the event horizon unharmed, or crash into a wall of fire?

The thing is, there is no "reality". Reality depends on the observer. There is "really" from Anna's point of view and "really" from your point of view. That's all.

Almost all. In the summer of 2012, physicists Ahmed Almheiri, Donald Marolph, Joe Polchinski, and James Sully, collectively known by their last names as AMPS, proposed a thought experiment that threatened to upend our understanding of black holes.

According to scientists, the resolution of the contradiction proposed by Süsskind is based on the fact that the disagreement in the assessment of what is happening between you and Anna is mediated by the event horizon. It doesn't matter if Anna actually saw one of your two specimens die in the fire of Hawking radiation, because the event horizon prevented her from seeing your second specimen flying deep into the black hole.

But what if Anna had a way to find out what was happening on the other side of the event horizon without crossing it?

General relativity tells us that this is impossible, but quantum mechanics blurs the hard rules a little. Anna could have peered beyond the event horizon with what Einstein called "spooky long-range action."

We are talking about quantum entanglement - a phenomenon in which the quantum states of two or more particles separated by space, mysteriously become interdependent. These particles now form a single and indivisible whole, and the information necessary to describe this whole is contained not in this or that particle, but in the relationship between them.

The idea put forward by AMPS is as follows. Suppose Anna picks up a particle near the event horizon - let's call it particle A.

If her version of what happened to you is true, that is, you were killed by Hawking radiation from the outside of the black hole, then particle A must be interconnected with another particle - B, which must also be located on the outside of the event horizon.

Image copyright Thinkstock Image caption Black holes can attract matter from nearby stars

If your vision of events corresponds to reality, and you are alive and well on the inside, then particle A must be interconnected with particle C, located somewhere inside the black hole.

The beauty of this theory is that each of the particles can only be interconnected with one other particle. This means that particle A is connected either to particle B or to particle C, but not to both at the same time.

So Anna takes her particle A and runs it through the entanglement decoding machine she has, which gives the answer whether this particle is associated with particle B or with particle C.

If the answer is C, your point of view has prevailed in violation of the laws of quantum mechanics. If particle A is connected to particle C, which is in the depths of a black hole, then the information describing their interdependence is forever lost to Anna, which contradicts the quantum law, according to which information is never lost.

If the answer is B, then, contrary to the principles of general relativity, Anna is right. If particle A is bound to particle B, you've really been incinerated by Hawking radiation. Instead of flying through the event horizon, as relativity requires, you crashed into a wall of fire.

So we're back to the question we started with - what happens to a person who gets inside a black hole? Will it fly through the event horizon unharmed thanks to a reality that is surprisingly dependent on the observer, or will it crash into a wall of fire ( blackholesfirewall, not to be confused with the computer termfirewall, "firewall", software that protects your computer on a network from unauthorized intrusion - Ed.)?

Nobody knows the answer to this question, one of the most controversial issues in theoretical physics.

For over 100 years, scientists have been trying to reconcile the principles of general relativity and quantum physics, in the hope that in the end one or the other will prevail. The resolution of the "wall of fire" paradox should answer the question of which of the principles prevailed and help physicists to create a comprehensive theory.

Image copyright Thinkstock Image caption Or maybe next time send Anna into a black hole?

The solution to the paradox of the disappearance of information may lie in Anna's deciphering machine. It is extremely difficult to determine with which other particle particle A is interconnected. Physicists Daniel Harlow of Princeton University in New Jersey and Patrick Hayden, now at Stanford University in California in California, wondered how long it would take.

In 2013, they calculated that even with the fastest computer possible according to physical laws, it would take Anna an extremely long time to decipher the relationship between particles - so long that by the time she gets the answer , the black hole will evaporate a long time ago.

If so, it is likely that Anna is simply not destined to ever know whose point of view is true. In this case, both stories will remain true at the same time, reality will depend on the observer, and none of the laws of physics will be violated.

In addition, the connection between highly complex calculations (of which our observer, apparently, is not capable) and the space-time continuum may prompt physicists to some new theoretical reflections.

Thus, black holes are not just dangerous objects on the way of interstellar expeditions, but also theoretical laboratories in which the slightest variations in physical laws grow to such a size that they can no longer be neglected.

If the true nature of reality lies somewhere, the best place to look for it is in black holes. But while we do not have a clear understanding of how safe the event horizon is for humans, it is safer to watch searches from the outside. In extreme cases, you can send Anna into the black hole next time - now it's her turn.