# Astrophysics Redshift Question

• stuartgriffin
In summary, the conversation discusses attempting to link equations and understanding how given data fits. The question of whether the angular radius is used as the deflection angle is raised, followed by the inquiry of how the distance to the lensed galaxy can aid in determining the deflection angle. The conversation also mentions calculating the distance using redshift and Hubble's constant, and questioning if the equations being used are correct.
stuartgriffin
Homework Statement
A galaxy cluster of mass 3.0 × 1013M⊙ with known distance of 20 Mpc is observed in the centre of a bright ring, which is presumably a lensed galaxy. The angular radius of the ring from the cluster is 1.13 arcmin. The ring is observed to have a redshift of 0.0075. Assuming a value of 70kms−1Mpc−1 for the Hubble constant, determine whether the ring’s redshift distance is consistent at an accuracy of ~5% to the distance expected for the lensed galaxy to actually be located directly behind the cluster.
Relevant Equations
a=4GM/bc^2
V=H0D
I have attempted to link the equations, but I don't really understand how the data given fits. Does the angular radius get plugged in as the deflection angle?

What is the distance to the lensed galaxy? How can this help you get the deflection angle?

stuartgriffin
Orodruin said:
What is the distance to the lensed galaxy? How can this help you get the deflection angle?

Ahhh, thank you, so I calculate the distance using the redshift and hubbles constant? Am I on the right lines with the equations I am using?

Orodruin said:
What is the distance to the lensed galaxy? How can this help you get the deflection angle?
Does this look like I'm headed on the right track?

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## What is redshift in astrophysics?

Redshift in astrophysics is a phenomenon where light from an object in space appears to have a longer wavelength, or is shifted towards the red end of the spectrum. This is caused by the object moving away from the observer, and is a result of the expansion of the universe.

## How is redshift measured?

Redshift is typically measured by observing the spectrum of light from an object and comparing it to a known spectrum. The amount of redshift is determined by the difference in the wavelengths of certain spectral lines.

## What causes redshift?

Redshift is primarily caused by the expansion of the universe, where objects are moving away from each other due to the stretching of space. It can also be caused by the Doppler effect, where the motion of an object towards or away from an observer affects the perceived wavelength of light.

## What is the difference between redshift and blueshift?

Redshift and blueshift are opposite effects, where redshift is an increase in the wavelength of light and blueshift is a decrease in wavelength. Redshift is caused by objects moving away from an observer, while blueshift is caused by objects moving towards an observer.

## What can redshift tell us about the universe?

Redshift can provide valuable information about the age and expansion of the universe. By measuring the amount of redshift in different objects, scientists can determine the rate of expansion and the distance of these objects from Earth. Redshift can also be used to study the evolution of galaxies and the distribution of matter in the universe.

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