Gravitational redshift and black holes

In summary, gravitational redshift causes light trying to escape a black hole to have its frequency reduced. This is due to the Equivalence Principle, which states that in a local inertial frame, the laws of physics are given by the laws of special relativity. When comparing two reference frames, where one is situated at a distance above the other in a gravitational field, the frame closer to the source of the gravitational field will receive the light at a lower frequency. This can be calculated using the weak field approximation. The physical cause of this redshift is the curvature of spacetime caused by the massive object, which affects the path and frequency of the light.
  • #1
niin
15
0
Questions: Gravitational redshift and black holes

I have some questions:

1. What does gravitational redshift do to light trying to escape a black hole? Is the light destroyed?

2. And what is the physical cause of this redshift? (I’m not interested in equations and math, only the physical cause).

I hope someone can help me. Thanks.
 
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  • #2
The beginning to understand gravitational redshift is the Equivalence Principle.

"In a local inertial frame the laws of physics are given by the laws of special relativity"

Now we have to reference frames S1 and S2, S1 situated at some distance above S2.
They are in a gravitational field.
S1 will always remain still and S2 will start free falling at t=0.

At t=0 we emit a photon from the origin to S2 towards S1.

... this continues but some math are required.

you can work out the frequency that S1 will receive if you use the weak field approximation.
 
  • #3
Kuon,
I don't see why the "equivalence principle" should solve it. If you think of the first reference frame as being accelerated, then there is no redshift, because both reference frame must be accelerated or the distance would change between them. And it's not the distance that changes in this case. Right?
 

Related to Gravitational redshift and black holes

1. What is gravitational redshift and how does it relate to black holes?

Gravitational redshift is a phenomenon in which light is stretched to longer wavelengths as it travels out of a gravitational field. It is directly related to black holes because their immense gravitational pull can significantly affect the wavelength of light, making it appear redshifted to an external observer.

2. How does the escape velocity of a black hole affect gravitational redshift?

The escape velocity of a black hole is directly related to its gravitational redshift. As the escape velocity of the black hole increases, the gravitational redshift also increases. This means that the light escaping from the black hole will appear more redshifted, indicating the immense strength of the black hole's gravitational pull.

3. Can gravitational redshift be observed in everyday life?

Yes, gravitational redshift can be observed in everyday life, although it may not be noticeable to the naked eye. For example, the GPS system on our phones and cars must take into account the gravitational redshift caused by the Earth's mass in order to accurately calculate our location. This is because the Earth's mass affects the speed of the satellites used in GPS, causing a slight redshift in the signals they send.

4. How does the theory of general relativity explain gravitational redshift in relation to black holes?

The theory of general relativity explains that gravity is not a force between masses, but rather a curvature of space and time caused by the presence of mass and energy. In the case of black holes, their immense mass creates a strong curvature in space-time, resulting in the gravitational redshift of light as it tries to escape the black hole's gravitational pull.

5. Can gravitational redshift be used to detect the presence of a black hole?

Yes, gravitational redshift can be used as a tool to detect the presence of a black hole. By observing the spectrum of light emitted from a region of space, astronomers can determine if the light has been redshifted, indicating the presence of a massive object with a strong gravitational pull, such as a black hole.

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