Measuring the Transverse Velocity of a Galaxy

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Homework Help Overview

The discussion revolves around measuring the transverse velocity of a galaxy using images taken over a span of time. Participants are trying to understand how to interpret the time data associated with these images and how to apply it to calculate velocity.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the method of calculating velocity using distance and time, questioning how to accurately determine the time from the provided figures. There is uncertainty about whether to consider the entire time span or specific intervals, and some participants express confusion about the relevance of the x-axis in their calculations.

Discussion Status

Some guidance has been offered regarding the approach to take measurements from the images and the possibility of simplifying the calculation by using only the first and last images. However, multiple interpretations of how to utilize the time data and the figures are being explored, indicating an ongoing discussion.

Contextual Notes

Participants are navigating the constraints of interpreting visual data and the specific requirements of the homework problem, including the need to clarify the time intervals and the significance of the distance measurements.

fishlens
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Homework Statement
In the figure below we see a component of a jet of a galactic nucleus which is moving away from its nucleus. The distance to the galactic nucleus is D. What is the observed apparent transverse velocity? And what is the value of the Lorentz factor needed to explain this motion?

Figure : https://imgur.com/a/t0m7kCr
Relevant Equations
gamma = 1/sqrt(1-(v/c)^2) (gamma - Lorentz factor, v - velocity, c - speed of light)
See the attached figure.

I understand that we look for the apparent transverse velocity v , for example through v = d/t (d - distance, t - time). The distance to the galactic nucleus is known as D. Though I am not sure how to read off the time from this figure.
 
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The numbers next to the images are (decimal) years. The first image is from mid 1977, the last from mid 1980.
 
Hi, thanks for the reply @m
mfb said:
The numbers next to the images are (decimal) years. The first image is from mid 1977, the last from mid 1980.

Thanks for the reply!

Yes, I assumed that it was the time in years. Though, I am not sure if we should take the time span to be the whole time difference between mid 1977 to mid 1980. Why should we do this? I am confused about this. Also, are we not supposed to use the x-axis in some way? Sorry for maybe dumb questions.
 
The best approach is to find the separation between galaxy and jet in all 5 images and to make a linear fit. For a homework problem it should be acceptable to just take the first and last image.That's the distance between us and the galaxy, not the distance between jet and galaxy.
 
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