MadSci Network: Physics

Re: what happens to light when bent by a gravitational force

Date: Fri Oct 13 09:15:28 2000
Posted By: Meghan Gray, Grad student, Astronomy, Cambridge University
Area of science: Physics
ID: 969079213.Ph


The simple answer is that neither wavelength (and thus frequency, since
they are related) nor polarization of light is directly affected
in most of the weak gravitational fields in which we observe lensing to
occur.  The changes we do observe relate to the time the lensed
light takes to travel, the magnification of the light, the distortion of
the shape of the light bundles, and the longer path-lengths travelled.

However, in very strong gravitational fields (e.g. near a black hole or a
compact neutron star) where the bending angles are large the light will
experience a gravitational redshift and the observed wavelength would be
shifted longwards (become redder).

Finally, you can imagine scenarios where there is a net polarization or
wavelength change observed, not by the lensing itself but because of
secondary effects: for example if the magnification is not constant across
the source and different parts are lensed more strongly than others, or if
the light is reddened by passing through dust along the lensed light path.


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