# Light Entering Black Hole: Hawking Radiation Explained

• Superposed_Cat
In summary, the conversation discusses the potential blueshift of light when pulled towards a black hole and how this phenomenon is similar to the gravitational effect of a star of the same mass. The concept is illustrated with an example of two stationary observers shining flashlights at each other on a mountain.

#### Superposed_Cat

Hi all, I was wondering if, when a beam of light is pulled towards a black hole , because it can't accelerate, it is blueshifted? Thanks in advance.

Hi Superposed_Cat!

If two people with identical flashlights are stationary at the top and bottom of a mountain, shining the flashlights at each other,

the top person will see the light redshifted, and the bottom person will see the light blueshifted.

It's the same for stationary observers near a black hole …

the gravitational effect of a black hole is (outside the event horizon and outside the surface of the star) exactly the same as that of a star of the same mass.

Thanks tiny-tim :). Good day fine sir.

## 1. What is Hawking Radiation?

Hawking Radiation is a type of radiation that is theorized to be emitted by black holes. It is named after the physicist Stephen Hawking, who proposed its existence in 1974. This radiation is thought to be generated by quantum effects near the event horizon of a black hole, causing particles to be created and one to fall into the black hole while the other escapes.

## 2. How does light enter a black hole?

Light can enter a black hole through its event horizon, which is the point of no return. This is where the gravitational pull of the black hole is so strong that even light cannot escape. Once light crosses the event horizon, it is pulled into the black hole and cannot be seen from the outside.

## 3. Does Hawking Radiation mean that black holes eventually disappear?

Yes, according to the theory of Hawking Radiation, black holes do eventually disappear. This is because as particles are being created and one falls into the black hole, the other escapes and carries away energy. This energy loss causes the black hole to slowly shrink and eventually evaporate.

## 4. How does Hawking Radiation affect the lifespan of a black hole?

The existence of Hawking Radiation means that black holes have a limited lifespan. As they emit this radiation, they lose energy and eventually evaporate. The amount of time it takes for a black hole to completely evaporate depends on its mass, with smaller black holes evaporating faster than larger ones.

## 5. Has Hawking Radiation been observed?

No, Hawking Radiation has not yet been directly observed. This is because the amount of radiation emitted by black holes is incredibly small and difficult to detect. However, there is indirect evidence of its existence, such as the observation of black holes losing mass over time, which supports the theory of Hawking Radiation.