How black is a black hole?

are black holes really black? There is a saying that black holes are not black. So is the black hole black or not?

The black hole is one of the most mysterious celestial bodies in the universe, which can't be directly observed or caught by the astronomical telescope. A black hole is a celestial body with the largest mass and density discovered by humans so far, which is formed by the accretion of surrounding objects in the late stage of star evolution or binary star system. Because with the increase of mass, the gravity of celestial bodies will become more and more horrible, when a beam of light skips from a massive celestial body, the original linear orbit of the light will be slightly deflected by gravity. Then when a beam of light skips the black hole, it will be directly influenced by gravity and directly change its original orbit and go straight to the center of the black hole. It seems that the gravity of the black hole is so great that even light can't escape.

how do people see objects again? Because human beings see an object because it is illuminated by a light source and then reflected into human eyes, and finally imaged on the retina, and then processed by the brain and fed back to us what we saw. Then, since even the light can't escape in the area of the black hole, naturally there will be no light emitted or reflected from the black hole to let our eyes receive the signal. So we can't see the black hole. Because we can't observe black holes, people think they are black! Actually, that's not the case. If light can escape from the black hole, the color that the black hole presents to us may not necessarily be black.

how black is a black hole? It can be said that it is blacker than black.

The black things we usually see actually have their own light, such as black things, which can actually reflect some light and be witnessed. For example, in the dark, there is no starlight, moonlight and lights, which can be said to be dark enough. However, there are many things in nature that can emit infrared light or even X-rays, and many things that can emit visible light, so we can adapt to it for a while in the dark.

The blackest scene we can feel is being locked in a room with no light and no light coming in. There is no blacker scene! However, even if we can't see anything, there are actually infrared light emitted by objects inside and outside the room with our own heat. Some animals that can perceive infrared light can also see objects inside the room.

But a black hole is different. It is so black that we can't see anything, and it can't emit infrared light, X-rays or gamma rays. All electromagnetic waves will be absorbed into it by its strong gravitational field near it, so it can be said that it is so black that we can't perceive any electromagnetic rays about it, which is darker than what we know as "black".

Some friends may say that there is Hawking radiation in a black hole, but in fact Hawking radiation is very weak for a black hole, and this phenomenon only occurs at the edge of the event horizon of the black hole, and things inside the black hole are still invisible, so the black hole can be said to be black beyond imagination.

However, in our universe, it is very likely that there are no completely invisible black holes. On the contrary, they are all very bright. For example, Ton618, the brightest celestial body in the universe, is a black hole. What's the matter?

In fact, the main reason is that the gravitational field of a black hole is very strong, and the matter in the universe is not scarce, so no matter where the black hole is, there are more or less substances sucked by it. In the process of being sucked in, the substances will be torn and decomposed by it, such as stars and planets, which will be dispersed into gas clusters or small rocks, and then further torn into dust and gas, and then molecules will be pulled into atoms, and then the atoms will be broken, and the substances will be torn into quarks.

So, although it is theoretically thought that black holes are too dark to see anything, it is almost impossible for black holes in the universe not to absorb substances, so they all emit light, but the luminosity is different due to the difference in mass and the amount of absorbed substances.

black holes are like idealized absolute blackbodies, they absorb electromagnetic waves in all bands. But black holes are different from blackbodies, because blackbodies themselves radiate electromagnetic waves, and when the temperature exceeds a certain threshold, blackbodies even radiate visible light. Black holes, on the other hand, hardly radiate electromagnetic waves, so black holes are the darkest celestial bodies known in the universe, and they cannot be directly observed by electromagnetic waves at present.

the reason why a black hole is so black is related to its extreme gravitational field. When a supernova explosion occurs in a massive star, the matter in the core region will be severely squeezed by its own gravity, which will make them unable to maintain their normal state. The final neutron degeneracy pressure can't resist gravitational collapse, and all the matter will collapse into an infinitesimal singularity. According to the general theory of relativity, the singularity will make the surrounding space extremely curved, especially the space in a certain range will be curved to the extent that even light can't escape. This range and singularity are black holes.

However, according to Hawking's radiation theory, the black hole is not completely radiation-free, and there will still be very little energy escaping from the black hole, which will lead to the decline of the quality of the black hole. However, the temperature of Hawking radiation is extremely low, which is theoretically only one hundredth of a degree higher than absolute zero, which is far lower than the average temperature of the universe of 2.73 Kelvin. If you shine a beam of light on a black hole, it will weaken Hawking radiation, so the black hole will become darker instead. Therefore, it is almost impossible for us to directly observe the black hole itself by means of electromagnetic waves.

About how black a black hole is, we can refer to Vantablack, the blackest substance produced by human beings at present:

This is a black body made of carbon nanotubes, which can absorb up to 99.96% of visible light. In contrast, black holes are much darker than this material.

In addition, although black holes themselves are almost completely black, they will devour the surrounding matter and form a bright accretion disk around themselves, which can be observed.

black holes are invisible to human eyes. People guess that there is a star based on the abnormal bending of various rays and waves in the universe, and its gravity and mass are infinite, so that light can't get rid of it. So people can't observe black holes, which can be understood as infinite darkness. Moreover, although the black hole exists in theory, it is only a theory, and there is no absolute evidence that there is such a star as a black hole.

a: a black hole is an ideal black body, and "black" is reflected in the temperature of the black hole. A black hole with the mass of the sun has a Hawking radiation temperature of about 1^-8K. Even if it is placed in interstellar space, the black hole can absorb energy from the cosmic background radiation (temperature 2.7K).

Black holes also have temperature. For Schwarzschild black holes, the temperature of black holes is inversely proportional to their mass. The greater the mass of black holes, the lower the radiation temperature. Black holes can only enter and exit ordinary matter, and only through Hawking radiation can black holes lose mass.

According to Hawking radiation temperature formula of black holes, we can estimate the black holes with solar mass, and the radiation temperature is only 1^-8K. Then, according to Planck blackbody radiation formula, we can know that:

(1) The lower the temperature, the longer the wavelength of the maximum radiation energy;

(2) The lower the temperature is, the extreme value of radiation energy tends to zero;

So we get that a black hole the size of the sun will radiate electromagnetic waves, but the electromagnetic waves are seriously redshifted and the energy is extremely low; This will lead to a black hole with the mass of the sun, and the generated Hawking radiation is difficult to be observed. In fact, Hawking radiation has not been confirmed so far.

A black hole the size of the sun is almost pure black, absorbing all wavelengths of light, but hardly radiating electromagnetic waves; For a black hole temperature of 1^-8K, it is so dark that it can even absorb energy from cosmic background radiation.

However, in one case, the radiation temperature of a small black hole, such as a black hole with a mass of one billion tons, will reach 1 trillion degrees, which can be detected. Such a miniature black hole can only be produced in BIGBANG, and it only exists in theory at present.

A black hole is formed by the collapse of a massive star into a superred giant. We can only know three physical properties of a black hole, namely, spin, charge and mass. Even light in a black hole can't escape its powerful gravity, and the more it goes into the black hole, the greater the gravity. The horizon of the black hole is where gravity can just bind the light. We can't know the information within the horizon. What the black hole can actually observe is through its powerful gravitational effect. It is said that the black hole must radiate through Hawking

. A black hole is a space formed by energy. Then in the long run, energy must be converted into power to maintain stability. So where there is darkness, there is light. It is conceivable that the solar system is a black hole. Let's just live on the bright side of the black hole.

Only you can realize this

I think light enters a black hole! It was absorbed by the black hole! The black hole is too big! So after the light goes in! Still can't afford to shine a black hole! Matter is equal to or greater than one side! A tough light can illuminate a black hole! If the black hole is too big! The light can only be seen! Just like a flashlight shining on the dark earth is the same reason! If the sun shines on the earth! The sun is much bigger! So the earth can be fully illuminated!

a black hole is not black, but you can't see it.