Polarization (waves)
Polarization (also polarisation) is a property applying to transverse waves that specifies the geometrical orientation of the oscillations. In a transverse wave, the direction of the oscillation is perpendicular to the direction of motion of the wave. A simple example of a polarized transverse wave is vibrations traveling along a taut string "(see image)"; for example, in a musical instrument like a guitar string. Depending on how the string is plucked, the vibrations can be in a vertical direction, horizontal direction, or at any angle perpendicular to the string. In contrast, in longitudinal waves, such as sound waves in a liquid or gas, the displacement of the particles in the oscillation is always in the direction of propagation, so these waves do not exhibit polarization. Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, and transverse sound waves (shear waves) in solids. In some types of transverse waves, the wave displacement is limited to a single direction, so these also do not exhibit polarization; for example, in surface waves in liquids (gravity waves), the wave displacement of the particles is always in a vertical plane.
Chandrasekhar polarization
Chandrasekhar published series of 26 papers in The Astrophysical Journal titled "On the Radiative Equilibrium of a Stellar Atmosphere" from 1944 to 1948. In the 10th paper, he predicted that the purely electron stellar atmosphere emits a polarized light using Thomson law of scattering. The theory predicted that 11 percent polarization could be observed at maximum. But when this is applied to a spherical star, the net polarization effect was found to be zero, because of the spherical symmetry. But it took another 20 years to explain under what conditions this polarization can be observed. J. Patrick Harrington and George W. Collins, II showed that this symmetry is broken if we consider a rapidly rotating star (or a binary star system), in which the star is not exactly spherical, but slightly oblate due to extreme rotation (or tidal distortion in the case of binary system). The symmetry is also broken in eclipsing binary star system.