Problem 3. Consider a flat, single component universe. 1. For a light source at redshift z that is observed at time to, show that z changes at a rate Ho(1+2) - Ho(1+2)³(1+w)/2 dz dto (2.1) 2. For what values of w does the observed redshift increase with time? 3. Assuming the single component is matter and Ho = 68 km/s/Mpc, you observe a galaxy at z = 1. Using Equation 2.1, determine how long you will have to keep observing the galaxy in order to see its redshift change by 1 part in 106.

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Problem 3. Consider a flat, single component universe.
1. For a light source at redshift z that is observed at time to, show that z changes at a rate
dz
dto
=
= Ho(1 + 2) — Ho(1+2)³(¹+w)/2
(2.1)
2. For what values of w does the observed redshift increase with time?
3. Assuming the single component is matter and Ho = 68 km/s/Mpc, you observe a galaxy at z = 1. Using
Equation 2.1, determine how long you will have to keep observing the galaxy in order to see its redshift
change by 1 part in 106.
Transcribed Image Text:Problem 3. Consider a flat, single component universe. 1. For a light source at redshift z that is observed at time to, show that z changes at a rate dz dto = = Ho(1 + 2) — Ho(1+2)³(¹+w)/2 (2.1) 2. For what values of w does the observed redshift increase with time? 3. Assuming the single component is matter and Ho = 68 km/s/Mpc, you observe a galaxy at z = 1. Using Equation 2.1, determine how long you will have to keep observing the galaxy in order to see its redshift change by 1 part in 106.
Expert Solution
Step 1

Given a flat single-component universe.

 

1.)

 

The Hubble parameter is defined by

H(t)=1a(t)da(t)dt...(i)

And the relation between a, and z is given by

1+z=a(t0)a(te)...(ii)

Let dt0 and dte to the time of observation and the time the light was emitted.

Now taking dzdt0   we get

 

dzdt0=da(t0)dt01a(te)-a(t0)a2(te)da(te)d(t0)dzdt0=1a(t0)da(t0)dt0a(t0)a(te)-a(t0)a(te)1a(te)da(te)dtedtedt0using eqn(i) and eqn (ii) we getdzdt0=H(t0)(1+z)-H(te)a(t0)a(te)dtedt0...(iii) 

 

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