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Homework Help: A Question On Redshift

  1. Mar 23, 2010 #1
    A redshift survey has identified a galaxy cluster for which it infers a di stance of 520 Mpc. At what redshift is this cluster observed to be? You may use H0 = 72 km s−1 Mpc−1

    Now call me old fashioned but don't i need some kind of relativistic speed to calculate the redshift, i mean i have a distance of 520Mpc (=16.12x10^21m) and the hubble constant...but im sure i need a value for how fast its travelling away from me...


    EDIT i think i just realised that i times its distance by Ho to get its speed as its Kms-1 Mpc-1
  2. jcsd
  3. Mar 23, 2010 #2
    Your edit is correct.
  4. Mar 23, 2010 #3


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    Then as long as this speed is much less than 'c' you can just use classical redshift.
    When you get redshifts approaching (or larger than) 1 you need to take into account the expansion of the universe.
  5. Mar 23, 2010 #4
    yeah the Lorentz factor was 1.00... so i just used z=v/c
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