Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 26, Problem 7Q
To determine
The strength of
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The expanding universe is carrying distant objects away from each other at a rate proportional to their separations. We use the Doppler effect observed in spectra of distant galaxies and quasars to calculate recession speeds. For the most distant objects recession speeds approach c, and therefore, the relativistic Doppler shift expression must be used. We define the redshift, z, as the fractional change in wavelength.
a) The most distant quasar currently known is ULAS J1120+0641, discovered with the UK Infrared Telescope on Mauna Kea. It has a redshift of 7.1. Calculate its radial velocity in terms of v/c.
b) Determine the distance to this quasar.
c) At what wavelength would the Ha line (656.28 nm) be observed for this quasar?
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.
Chapter 26 Solutions
Universe: Stars And Galaxies
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