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Homework Help: Luminosity distance

  1. Apr 19, 2012 #1
    1. The problem statement, all variables and given/known data
    Hubble's law may be written as
    H0dL = z +(1/2)(1 - q0)z2
    Working to O(z) only, what is the redshift of a galaxy at a luminosity distance of 100 Mpc
    from Earth?
    What is the role of the constant q0? Given that observations show that q0 = -0.77,
    calculate the luminosity distance (in Mpc) of a high redshift supernova with z = 0.5.

    2. Relevant equations
    the first question is what O(z) might mean and second if i make the substitution ,q0 which is given later i get a quadratic equation with imaginary solutions.The second part is just a metter of calculations i suppose ,but it seems that for the first question im missing something.

    3. The attempt at a solution
  2. jcsd
  3. Apr 19, 2012 #2

    George Jones

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    Gold Member

    O(z) means leave out any powers of z that are higher than z, i.e., omit z^2, z^3, ...

    O(z)^2 means leave out any powers of z that are higher than z^2, i.e., omit z^3, z^4, ...
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