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Homework Help: [Astrophysics] CBR and angular size

  1. Apr 24, 2005 #1

    Assuming a flat universe, find the angular size of the largest causally connected region of the CBR. Hint: We see this region as it existed at the time of decoupling, when the CBR photons were set free.


    Alright, flat universe, k = 0, tdec --> z~= 1100

    Theta = (H0 * D / 2c) * ((1+z)^1.5) / ((1+z)^0.5)-1)

    H0 = Hubble constant
    D = Linear diameter
    c = constant speed of light

    I am stuck here. I can solve the z portion of the equation, but I don't know how to find the value of D, the causally connected section of the CBR. My guess is that I'm supposed to use the size of the universe at the tdec point (time just before the photons were set free). Any ideas?

  2. jcsd
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