"Black hole" can easily be imagined as a "big black hole", but it is not the case. The so-called "black hole" is a celestial body whose gravitational field is so strong that even light cannot escape.
According to general relativity, the gravitational field will bend space-time. When a star is very large, its gravitational field has little effect on space-time, and light emitted from a certain point on the star's surface can be emitted in a straight line in any direction. The smaller the radius of the star, the greater its effect on the curvature of the surrounding space-time, and the light emitted at certain angles will return to the star's surface along the curved space.
When the radius of the star reaches a certain value (called the "Schwarzschild radius" in astronomy), even the light emitted by the vertical surface is captured. At this point, the star becomes a black hole. Calling it "black" means that it is like a bottomless pit in the universe. Once any matter falls into it, it "seems" that it can never escape. In fact, black holes are truly "invisible", which we will talk about in a moment.
So, how are black holes formed? In fact, like white dwarfs and neutron stars, black holes are likely to evolve from stars.
We have introduced the formation process of white dwarfs and neutron stars in more detail. When a star ages, its thermonuclear reactions have exhausted the fuel (hydrogen) in the center, and there is not much energy produced by the center. In this way, it no longer has enough strength to bear the huge weight of the shell. Therefore, under the heavy pressure of the outer shell, the core begins to collapse until it finally forms a small and dense star that is able to balance with the pressure again.
Stars with smaller masses mainly evolve into white dwarfs, while stars with larger masses may form neutron stars. According to scientists' calculations, the total mass of a neutron star cannot be greater than three times the mass of the sun. If this value is exceeded, there will be no force left to contend with its own gravity, triggering another Big Crunch.
This time, according to scientists’ conjecture, matter will march inexorably toward the center point until it becomes a “point” where the volume tends to zero and the density tends to infinity. And once its radius shrinks to a certain extent (Schwarzschild radius), as we introduced above, the huge gravity will prevent even light from being emitted outward, thus cutting off all connections between the star and the outside world - " "Black Hole" was born.
Compared with other celestial bodies, black holes are too special. For example, black holes have "invisibility" and people cannot directly observe them. Even scientists can only make various conjectures about its internal structure. So, how do black holes hide themselves? The answer is - curved space. We all know that light travels in straight lines. This is the most basic common sense. However, according to the general theory of relativity, space will bend under the action of the gravitational field. At this time, although light still travels along the shortest distance between any two points, it is no longer a straight line, but a curve. Figuratively speaking, it seems that light was originally going to go in a straight line, but the strong gravity pulled it away from its original direction.
On Earth, this bending is minimal due to the small effect of the gravitational field. Around a black hole, this deformation of space is very large. In this way, even if a part of the light emitted by a star blocked by a black hole will fall into the black hole and disappear, the other part of the light will bypass the black hole in the curved space and reach the earth. Therefore, we can effortlessly observe the starry sky behind the black hole as if the black hole does not exist. This is the invisibility of the black hole.
What’s more interesting is that some stars not only emit light towards the earth directly to the earth, but the light they emit in other directions may also be refracted by the strong gravity of nearby black holes and reach the earth. In this way, we can not only see the "face" of the star, but also its sides and even its back at the same time!
"Black hole" is undoubtedly one of the most challenging and exciting astronomical theories of this century. Many scientists are working hard to unveil its mystery, and new theories are constantly being proposed. However, these latest results in contemporary astrophysics cannot be explained clearly in a few words here. Interested friends can refer to specialized works.
Black holes are extremely dense stars that absorb everything and even light cannot escape. (Some scientists now analyze that black holes do not exist in the universe. This requires further proof, but we can have different academic opinions. )
Additional note: When the space volume is infinitesimal (can be considered as 0) and the injected mass is close to infinite, and the field is infinitely strengthened, does the black hole really still exist?
Or the ultimate outcome of matter is not to turn into energy but to become an infinite field?
First of all, let’s give a visual explanation of the black hole:
The black hole has a huge gravitational force, and even light is attracted by it. There is a huge gravitational field hidden in the black hole. This gravitational force is huge. Nothing, not even light, can escape the grasp of a black hole. A black hole does not allow anything within its boundaries to be seen by the outside world, which is why such objects are called "black holes." We cannot observe it through the reflection of light and can only learn about a black hole indirectly through the surrounding objects that are affected by it. It is speculated that black holes are the remnants of dead stars or exploding gas clouds, created when special massive supergiants collapse and contract.
Let me explain it from a physical point of view:
A black hole is actually a planet (similar to a planet), but its density is very, very high, and objects close to it are affected by it. Bound by gravity (just like people on the earth have not flown away), no matter how high the speed, they cannot escape. For the earth, you can escape from the earth by flying at the second cosmic speed (11.2 km/s), but for a black hole, its third cosmic speed (16.7 km/s) is so great that it exceeds the speed of light. So even the light can't escape, so the light that goes in is not reflected back, and our eyes can't see anything, just black.
Because black holes are invisible, some people have always questioned whether black holes really exist. If they really exist, where are they?
The production process of a black hole is similar to the production process of a neutron star; the core of the star shrinks rapidly under its own weight and explodes violently. The contraction process stops immediately when all the matter in the core is turned into neutrons and is compressed into a dense planet. But in the case of a black hole, because the mass of the star's core is so large that the contraction process continues endlessly, the neutrons themselves are crushed into powder under the attraction of the squeezing gravity itself, and what is left is a material with an unimaginable density. . Anything that comes close to it is sucked in, and black holes become like vacuum cleaners
In order to understand the dynamics of black holes and understand how they keep everything inside from escaping, we need to discuss General relativity. General relativity is a theory of gravity created by Einstein, which applies to planets, stars, and black holes. This theory, proposed by Einstein in 1916, explains how space and time are distorted by the presence of massive objects. Simply put, general relativity says that matter curves space, and that the curvature of space in turn affects the motion of objects traveling through space.
Let’s see how Einstein’s model works. First, consider that time (the three dimensions of space are length, width, and height) is the fourth dimension in the real world (although it is difficult to draw a direction other than the usual three, we can try our best to imagine it). Second, consider space-time to be the surface of a giant taut gymnastic spring bed.
Einstein’s theory was that mass curves space-time. We might as well put a big stone on the bed of a spring bed to illustrate this situation: the weight of the stone makes the tightened bed sink slightly. Although the spring bed is still basically flat, its center is still flat. Slightly concave. If you place more stones in the center of a spring bed, it will have a greater effect, causing the bed surface to sink further. In fact, the more stones there are, the more the spring bed will flex.
Similarly, massive objects in the universe will distort the structure of the universe. Just as 10 stones curve the surface of a spring bed more than one stone, objects much more massive than the Sun curve space much more than objects of one solar mass or less.
If a tennis ball rolls on a taut, flat spring bed, it will move in a straight line. On the other hand, if it passes through a concave place, its path will be arc-shaped. In the same way, celestial bodies traveling through flat areas of space-time continue to move in straight lines, while those traveling through curved areas will move along curved trajectories.
Now let’s take a look at the impact of a black hole on the space-time region around it. Imagine a very massive stone placed on a bed of springs to represent an extremely dense black hole. Naturally, stones will greatly affect the bed surface, not only causing its surface to bend and sink, but may also cause the bed surface to break. A similar situation can also occur in the universe. If there is a black hole in the universe, the structure of the universe will be torn apart. This break in the fabric of space-time is called a singularity or singularity of space-time.
Now let’s look at why nothing can escape from a black hole. Just as a tennis ball rolling over a spring bed will fall into a deep hole formed by a large rock, an object passing through a black hole will be captured by its gravitational trap. Moreover, an infinite amount of energy is required to save an unlucky object.
We have already said that nothing can enter a black hole and escape from it. But scientists believe black holes release their energy slowly. The famous British physicist Hawking proved in 1974 that black holes have a non-zero temperature and a temperature that is higher than that of their surroundings. According to the principles of physics, all objects with a higher temperature than their surroundings will release heat, and black holes are no exception. A black hole will continue to emit energy for millions of trillions of years. The energy released by the black hole is called Hawking radiation. A black hole dissipates all its energy and disappears.
The black hole between time and space slows down time and makes space elastic, while swallowing everything that passes through it. In 1969, American physicist John Wheeler named this insatiable space a "black hole."
We all know that because black holes cannot reflect light, they are invisible. Black holes may appear distant and dark in our minds. But the famous British physicist Hawking believes that black holes are not as black as most people think. Through scientists' observations, there is radiation around the black hole, and it is likely to come from the black hole. In other words, the black hole may not be as black as imagined. Hawking pointed out that the source of radioactive material in black holes is a kind of real particles. These particles are produced in pairs in space and do not obey the usual laws of physics. And after these particles collide, some will disappear into the vast space. Generally speaking, we may not even get a chance to see these particles until they disappear.
Hawking also pointed out that when black holes are created, real particles will appear in pairs. One of the real particles will be sucked into the black hole, and the other will escape. A bunch of escaping real particles will look like photons. To an observer, seeing escaping real particles is like seeing rays from a black hole.
So, to quote Hawking, "The black hole is not as black as imagined." It actually emits a large number of photons.
According to Einstein's law of conservation of energy and mass. When an object loses energy, it also loses mass. Black holes also obey the law of conservation of energy and mass. When a black hole loses energy, the black hole ceases to exist. Hawking predicted that the moment a black hole disappears, there will be a violent explosion, releasing energy equivalent to the energy of millions of hydrogen bombs.
But don’t look up expecting to see a fireworks show. In fact, after a black hole explodes, the energy released is very large and may be harmful to the body. Moreover, the time for energy release is also very long, some exceeding 10 billion to 20 billion years, which is longer than the history of our universe, and it will take trillions of years to completely dissipate the energy
" It is easy for people to imagine a "black hole" as a "big black hole", but it is not. The so-called "black hole" is a celestial body whose gravitational field is so strong that even light cannot escape.
According to the general theory of relativity, the gravitational field will bend space-time. When a star is very large, its gravitational field has little effect on space-time, and light emitted from a certain point on the star's surface can be emitted in a straight line in any direction. The smaller the radius of the star, the greater its effect on the curvature of the surrounding space-time, and the light emitted at certain angles will return to the star's surface along the curved space.
When the radius of the star is less than a certain value (called the "Schwarzschild radius" in astronomy), even the light emitted by the vertical surface is captured. At this point, the star becomes a black hole. Calling it "black" means that once any substance falls in, it can no longer escape, including light. In fact, black holes are truly "invisible", which we will talk about in a moment.
The formation of black holes
Like white dwarfs and neutron stars, black holes are likely to evolve from stars.
When a star ages, its thermonuclear reactions have exhausted the fuel (hydrogen) in the center, and there is not much energy produced by the center. In this way, it no longer has enough strength to bear the huge weight of the shell. Therefore, under the heavy pressure of the outer shell, the core begins to collapse until it finally forms a small and dense star that is able to balance with the pressure again.
Stars with smaller masses mainly evolve into white dwarfs, while stars with larger masses may form neutron stars. According to scientists' calculations, the total mass of a neutron star cannot be greater than three times the mass of the sun. If this value is exceeded, there will be no force left to contend with its own gravity, triggering another Big Crunch.
This time, according to scientists’ conjecture, matter will march inexorably toward the center point until it becomes a small object with a very small volume and a large density. And once its radius shrinks to a certain extent (must be smaller than the Schwarzschild radius), as we introduced above, the huge gravity will prevent even light from being emitted outward, thus cutting off all connections between the star and the outside world - —The "black hole" was born.
Special black holes
Compared with other celestial bodies, black holes are too special. For example, black holes have "invisibility" and people cannot directly observe them. Even scientists can only make various conjectures about its internal structure. So, how do black holes hide themselves? The answer is - curved space. We all know that light travels in straight lines. This is the most basic common sense. However, according to the general theory of relativity, space will bend under the action of the gravitational field. At this time, although light still travels along the shortest distance between any two points, it is no longer a straight line, but a curve. Figuratively speaking, it seems that light was originally going to go in a straight line, but the strong gravity pulled it away from its original direction.
On Earth, because the gravitational field has a small effect, this bending is minimal. Around a black hole, this deformation of space is very large. In this way, even if a part of the light emitted by a star blocked by a black hole will fall into the black hole and disappear, the other part of the light will bypass the black hole in the curved space and reach the earth. Therefore, we can effortlessly observe the starry sky behind the black hole as if the black hole does not exist. This is the invisibility of the black hole.
What’s more interesting is that not only the light emitted by some stars towards the earth can reach the earth directly, but the light emitted in other directions may also be refracted by the strong gravity of nearby black holes and reach the earth. In this way, we can not only see the "face" of the star, but also its sides and even its back at the same time!
"Black hole" is undoubtedly one of the most challenging and exciting astronomical theories of this century. Many scientists are working hard to unveil its mystery, and new theories are constantly being proposed. However, these latest results in contemporary astrophysics cannot be explained clearly in a few words here. Interested friends can refer to specialized works.
Based on composition, black holes can be divided into two major categories. One is a dark energy black hole, and the other is a physical black hole. Dark energy black holes are mainly composed of huge dark energy rotating at high speed, and there is no huge mass inside them. The huge dark energy rotates at a speed close to the speed of light, and a huge negative pressure is generated inside it to swallow objects, thus forming a black hole. For details, please see the "Cosmic Black Hole Theory". Dark energy black holes are the basis for the formation of galaxies, as well as the formation of star clusters and galaxy clusters. A physical black hole is formed by the collapse of one or more celestial bodies and has a huge mass. When the mass of a physical black hole is equal to or greater than the mass of a galaxy, we call it a singularity black hole. Dark energy black holes are very large and can be as large as the solar system. But the volume of a physical black hole is very small, and it can shrink to a singularity.
Black hole accretion
Black holes are usually discovered because they gather gas around them to produce radiation, a process called accretion. The efficiency of high-temperature gas radiating thermal energy will seriously affect the geometric and dynamic characteristics of the accretion flow. Thin disks with higher radiative efficiency and thick disks with lower radiative efficiency have been observed. As accreting gas approaches the central black hole, the radiation they produce is extremely sensitive to the black hole's rotation and the existence of an event horizon. Analysis of the luminosity and spectrum of accreting black holes provides strong evidence for the existence of rotating black holes and event horizons. Numerical simulations also show that the relativistic jets that often occur in accreting black holes are partly driven by the black hole's rotation.
Astrophysicists use the word "accretion" to describe the flow of matter toward a central gravitational body or central extended matter system. Accretion is one of the most common processes in astrophysics, and it is responsible for many of the common structures around us. In the early universe, galaxies formed when gas flowed toward the center of a gravitational potential well created by dark matter. Even today, stars are formed by the collapse and fragmentation of gas clouds under their own gravity, and then by accreting surrounding gas. Planets - including Earth - also form from the accumulation of gas and rock around newly formed stars. But when the central object is a black hole, accretion is at its most spectacular.
However, the black hole does not absorb everything, it also emits protons to the outside.
Exploding black hole
The black hole will emit dazzling light and shrink in size , or even explode. When British physicist Stephen Hawking created this language in 1974, the entire scientific community was shocked. Black holes were once considered to be the final settlement of the universe: nothing can escape from black holes. They swallow up gas and stars, and their mass increases, so the size of the hole will only increase. Hawking's theory is a leap of thinking driven by inspiration. He combined general relativity and quantum theory. He found that the gravitational field around the black hole releases energy while consuming the black hole's energy and mass. This "Hawking radiation" is negligible for most black holes, while small black holes radiate energy at an extremely high speed until the black hole's explode.
The wonderful shrinking black hole
When a particle escapes from a black hole without repaying the energy it borrowed, the black hole loses the same amount of energy from its gravitational field, and Einstein's formula E=mc^2 shows that the loss of energy results in the loss of mass. Therefore, the black hole will become lighter and smaller.
Boil until destruction
All black holes evaporate, but large black holes boil more slowly, and their radiation is very weak, making them difficult to detect. But as the black hole gets smaller, this process accelerates and eventually gets out of control. When a black hole becomes weak, the gravitational force will also become steeper, producing more escape particles, and the more energy and mass will be robbed from the black hole. The black hole enlarges faster and faster, causing the evaporation rate to become faster and faster, and the surrounding halo becomes brighter and hotter. When the temperature reaches 10^15℃, the black hole will be destroyed in an explosion.
Article about black holes:
Since ancient times, human beings have been dreaming of flying into the blue sky, but no one knows that there is a huge black space beyond the blue sky. In this space there is light, water, and life. Our beautiful Earth is one of them. Although the universe is so colorful, it is also full of dangers here. Asteroids, red giants, supernova explosions, black holes...
Black holes, as the name suggests, are invisible materials with super attractive force. Ever since Einstein and Hawking deduced the existence of such a substance through speculation and theory, scientists have been constantly exploring and searching to avoid the destruction of our planet.
The relationship between black holes and the destruction of the earth
A black hole is actually a mass of matter with a very large mass, and its gravitational force is extremely large (so far, no object with a greater gravitational force has been found) material), forming a deep well. It is formed by the continuous collapse of stars with extremely high mass and density. When the material core inside the star undergoes extremely unstable changes, an isolated point called a "singularity" will be formed (for details, please refer to Einstein's Generalized relativity). It will suck in all matter that enters the horizon, and nothing can escape from there (including light). He has no specific shape and cannot see it. He can only judge its existence based on the direction of the surrounding planets. Maybe you will scream in fear because of its mystery, but in fact there is no need to worry too much. Although it has a strong attraction, at the same time this is also an important evidence to judge its location, even if it is far away When the Earth's very close material has an impact, we still have enough time to save it, because its "formal boundary" is still far away from us at that time. Moreover, most stars will become neutron stars or white dwarfs after they collapse. But this does not mean that we can relax our vigilance (who knows whether we will be sucked in next moment?), which is one of the reasons why humans study it.
Stars, white dwarfs, neutron stars, quark stars, and black holes are stars with five density equivalents in sequence. The smallest density is of course the star. The black hole is the ultimate form of matter. After the black hole, the Big Bang will occur. Energy After it is released, it enters a new cycle.
In addition, black holes refer to places in the network where email messages are lost or Usenet announcements disappear.
Proposal of the name black hole
The term black hole only appeared not long ago. It was a name coined in 1969 by American scientist John Wheeler to vividly describe an idea that goes back at least 200 years. At that time, there were two theories of light in the world: one was the particle theory of light that Newton supported; the other was the wave theory of light. We now know that both are actually true. Due to the wave-particle duality of quantum mechanics, light can be considered both a wave and a particle. In the wave theory of light, it is unclear how light responds to gravity. But if light was made of particles, one would expect them to be affected by gravity just like cannonballs, rockets, and planets. At first it was thought that light particles move infinitely fast, so gravity cannot slow them down, but Roehmer's discovery of the finite speed of light showed that gravity could have an important effect.
In 1783, John Mitchell, the superintendent of Cambridge, published an article in the "Philosophical Transactions of the Royal Society of London" based on this assumption. He pointed out that a star with enough mass and compactness would have such a strong gravitational field that even light cannot escape - any light emitted from the star's surface will be attracted by the star's gravity before it reaches the distance. return. Mitchell suggested that there may be a large number of such stars, and although we cannot see them because the light from them does not reach us, we can still feel the pull of their gravity. This is exactly what we now call a black hole. It is literally a black void in space. A few years later, the French scientist Marquis de Laplace apparently independently proposed an idea similar to Michel's. It is very interesting that Laplace only included this idea in the first and second editions of his book The System of the World, and omitted it from later editions, probably thinking it was a folly. concept. (Also, the particle theory of light became unfashionable in the 19th century; it seemed that everything could be explained by wave theory, and according to wave theory, it was unclear whether light was affected by gravity.)
Facts Because the speed of light is fixed, it is very inconsistent to treat light like a cannonball in Newton's theory of gravity. (A cannonball fired from the ground slows down due to gravity, and finally stops rising and returns to the ground; however, a photon must continue upward at a constant speed, so how does Newtonian gravity affect light?) Until 1915, Einstein proposed Before general relativity, there was no theory of how gravity affected the coordination of light. It took even a long time before the implications of this theory for massive stars were understood.
In order to understand how black holes form, we first need to understand the life cycle of a star. Initially, a large amount of gas (mostly hydrogen) is attracted by its own gravity and begins to collapse on itself to form stars. As it contracts, the gas atoms collide with each other more and more frequently and at greater and greater speeds—the temperature of the gas rises. Eventually, the gas becomes so hot that when hydrogen atoms collide, they no longer bounce off but coalesce to form helium. Like a controlled hydrogen bomb explosion, the heat released in the reaction causes the star to glow. This added heat increases the pressure of the gas until it is enough to balance the gravitational pull, at which point the gas stops contracting. It's a bit like a balloon - there's a balance between the internal air pressure trying to inflate the balloon and the tension of the rubber trying to deflate it. The balance of heat emanating from nuclear reactions and gravitational attraction allows stars to maintain this balance over long periods of time. Eventually, however, the star exhausts its hydrogen and other nuclear fuel. This may seem like a big mistake, but it is not true. The more fuel a star initially has, the faster it burns out. This is because the more massive a star is, the hotter it must be to resist gravity. And the hotter it is, the faster its fuel is used. Our sun probably has enough energy to burn for another 5 billion years or so, but more massive stars can use up their fuel in as little as 100 million years, a time scale much shorter than the age of the universe. When a star runs out of fuel, it cools and begins to shrink. What happened next was only first understood in the late 2020s.
In 1928, an Indian graduate student - Saramanian Chandrasekhar - came to Cambridge, England by boat to study with the British astronomer Sir Arthur Eddington (a general theorist of relativity). home) study. (According to records, in the early 1920s, a reporter told Eddington that he had heard that only three people in the world understood general relativity. Eddington paused, then replied: "I was thinking of this third person." Who?") During his journey from India to England, Chandrasekhar calculated how large a star could continue to sustain itself against its own gravity after exhausting all its fuel. The idea is that as a star gets smaller, the particles of matter get very close together, and according to the Pauli Exclusion Principle, they must have very different velocities. This causes them to spread apart from each other and attempt to expand the star. A star can keep its radius constant by balancing the effects of gravity and the repulsive forces caused by the exclusion principle, just as gravity is balanced by heat early in its life.
However, Chandrasekhar realized that there was a limit to the repulsive force that the exclusion principle could provide. The maximum velocity difference of particles in a star is limited by relativity to the speed of light. This means that when a star becomes compact enough, the repulsive force caused by the exclusion principle becomes smaller than the gravitational force. Chandrasekhar calculated that a cold star about one and a half times the mass of the Sun cannot support itself against its own gravity. (This mass is now called the Chandrasekhar limit.) Soviet scientist Lev Davidovich Landau made a similar discovery at about the same time.
This has great significance for the final fate of massive stars. If a star is less massive than the Chandrasekhar limit, it will eventually stop shrinking and become a "white dwarf" with a radius of several thousand miles and a density of several hundred tons per cubic inch. A white dwarf is supported by the exclusion principle repulsion between electrons in its matter. We observe a large number of these white dwarfs. The first one to be observed was one orbiting Sirius, the brightest star in the night sky.
Landau pointed out that there is another possible final state for stars. Its ultimate mass is about one or two times the mass of the sun, but its volume is even much smaller than a white dwarf. These stars are supported by the exclusion principle repulsion between neutrons and protons, rather than between electrons. That's why they are called neutron stars. They have a radius of only about 10 miles and a density of several hundred million tons per cubic inch. When neutron stars were first predicted, there was no way to observe them. In fact, they were not observed until much later.
On the other hand, stars more massive than the Chandrasekhar limit present a big problem when they run out of fuel: under certain circumstances, they explode or are ejected Enough matter to reduce its own mass below the limit to avoid catastrophic gravitational collapse. But it's hard to believe that this would happen no matter how big the star is. How do you know it must have lost weight? Even if every star manages to lose enough weight to avoid collapse, what happens if you add more mass to a white dwarf or neutron star, pushing it past the limit? Will it collapse to infinite density? Eddington was shocked by this and refused to believe Chandrasekhar's results. Eddington believed that it was impossible for a star to collapse into a point. This is the view of most scientists: Einstein himself wrote a paper declaring that the volume of stars does not shrink to zero. Hostility from other scientists, especially his former teacher Eddington, the leading authority on stellar structure, led Chandrasekhar to abandon this work and study other astronomical problems such as the motion of star clusters. However, he won the 1983 Nobel Prize, at least in part, for his early work on the mass limit of cold stars.
Chandrasekhar pointed out that the exclusion principle cannot prevent stars with masses greater than the Chandrasekhar limit from collapsing. But what would happen to such a star according to general relativity? This problem was first solved in 1939 by a young American, Robert Oppenheimer. However, the results he obtained showed that observing with the telescopes of the time would no longer yield any results. Later, due to the interference of World War II, Oppenheimer himself was very closely involved in the atomic bomb project. After the war, the problem of gravitational collapse was largely forgotten as most scientists were drawn to physics at the atomic and nuclear scale.
Now, we have a picture from Oppenheimer's work: the gravitational field of the star changes the path of the light, making it different from the original path without the star. A light cone represents the path that light travels through space and time after being emitted from its top. The light cone is slightly deflected inward near the star's surface, and this deflection can be seen when observing the light from distant stars during a solar eclipse. As the star shrinks, the gravitational field on its surface becomes stronger, deflecting light inward more, making it more difficult for light to escape from the star. To a distant observer, the light becomes dimmer and redder. Finally, when the star shrinks to a certain critical radius, the gravitational field on the surface becomes so strong that the light cone is deflected inward so much