The polarization of the CMB detected in the WMAP data is evidence for which of the following? A. The first stars had enough mass to change lens the light around them, which polarized the light. B. The first stars acted as polarizing lenses as the CMB passed through them. C. The first stars gave off strong enough radiation to ionize most of the hydrogen gas in the universe, which in turn, polarized the light. D. The first stars, themselves, gave off this polarized light. Solution Answer is (c) Long time back ago perhaps 200 million years after big bang, the evolution of universe is started. when first star started shining then it light reionizes thehydrogen. result from WMAP show that re-ionization started too early as redshift z-20. and it is alsofound that re-ionization process was ongoing when redshift z-6that was a billion years after the Big Bang.it has been found that At this late stage in the evolution of the Universe,the density of hydrogen was much lower than atrecombination. Hence, even though hydrogen isfully ionized, only a fraction of the CMB photonsscattered with electrons after this re-ionization. Ascattering percentage somewhere around 10% to20% is the value favored in the latest analysis ofWMAP data. Even though only a fraction of thephotons scatter after re-ionization, this still has adramatic effect on the production of polarizationon large angular scales, of order ten degrees. Onthese scales the polarization produced atdecoupling (z ~ 1100) is minimal because thesescales are much larger than the mean free path atdecoupling. Thus, the signal from re-ionizationdetermines the shape of the power spectrum atlarge scales..

1. The polarization of the CMB detected in the WMAP data is evidence for which of the following?
A. The first stars had enough mass to change lens the light around them, which polarized the
light.
B. The first stars acted as polarizing lenses as the CMB passed through them.
C. The first stars gave off strong enough radiation to ionize most of the hydrogen gas in the
universe, which in turn, polarized the light.
D. The first stars, themselves, gave off this polarized light.
Solution
Answer is (c)
Long time back ago perhaps 200 million years after big bang, the evolution of universe is started.
when first star started shining then it light reionizes thehydrogen. result from WMAP show that
re-ionization started too early as redshift z-20. and it is alsofound that re-ionization process was
ongoing when redshift z-6that was a billion years after the Big Bang.it has been found that At
this late stage in the evolution of the Universe,the density of hydrogen was much lower than
atrecombination. Hence, even though hydrogen isfully ionized, only a fraction of the CMB
photonsscattered with electrons after this re-ionization. Ascattering percentage somewhere
around 10% to20% is the value favored in the latest analysis ofWMAP data. Even though only a
fraction of thephotons scatter after re-ionization, this still has adramatic effect on the production
of polarizationon large angular scales, of order ten degrees. Onthese scales the polarization
produced atdecoupling (z ~ 1100) is minimal because thesescales are much larger than the mean
free path atdecoupling. Thus, the signal from re-ionizationdetermines the shape of the power
spectrum atlarge scales.