Flux, Luminosity, Distance, Size

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SUMMARY

This discussion focuses on calculating distances and sizes of galaxy clusters using established astronomical formulas. The distance to Cluster A is determined to be 50 Mpc, leading to the conclusion that Cluster B, which is 16 times fainter, is located 200 Mpc away. Additionally, the relationship between the apparent size of galaxies in Cluster B compared to Cluster A is explored, with the understanding that greater distance results in smaller apparent sizes. The scale factor of the universe at redshift 0.8 is also discussed in relation to gravitational interactions between galaxies.

PREREQUISITES
  • Understanding of flux and luminosity equations in astrophysics
  • Familiarity with Cepheid variable stars for distance measurement
  • Knowledge of redshift and its implications in cosmology
  • Basic grasp of gravitational interactions between celestial bodies
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  • Study the application of the flux-luminosity-distance relationship in astrophysics
  • Learn about Cepheid variable stars and their role in measuring cosmic distances
  • Research the concept of redshift and its effects on the scale of the universe
  • Explore gravitational dynamics in multi-body systems in cosmology
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Astronomers, astrophysics students, and anyone interested in understanding the relationships between distance, luminosity, and size in the context of galaxy clusters.

kingwinner
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1) You observed two galaxy clusters. You have determined the distance to Cluster A (by Cephied variables) to be 50 Mpc. You find the galaxies in Cluster B to be on average 16 times fainter than those in Cluster A. How far away is Cluster B? How does the (apparent) average size of galaxies in Cluster B compared to that of Cluster A?
[Using the formula flux=luminosity/(4*pi*d^2), I have that the answer to the first part is 200 Mpc, but I don't know how to do the second part (in red), can someone please help me?]


2) The scale factor of the universe R(t) is equal to 1 (by definition) at the current epoch. This question compares the universe at a redshift of 0.8 to today.
If 2 galaxies were in each other's gravitational potential, and orbiting each other with an orbital of 0.5 Mpc at z=0.8. Assuming the orbit is stable, how far apart are they today?
[can someone give me some hints? I really have no clue how to calculate this...]

Thanks a lot!:smile:
 
Last edited:
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If the object is farther, the object's apparent size should be smaller...but what is the exact relationship?
 
Can anyone please help me?
 

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