Abstract
The principal testing ground for general relativity is the observable Universe. Gravitational lensing is the leading observational technique that gives insight into the distribution of baryonic matter in the stellar, galactic and cosmological scale, as well as the distribution of dark matter and dark energy, due to their gravitational interaction. Interpretation of ever more precise observational data requires increasingly subtle analytical techniques. In this paper, I discuss a formalism that can handle a nonlinear superposition of gravitational and refractive lensing by a grouping of baryonic matter, dark matter and dark energy for a given distribution of those entities (i.e. for a given spacetime metric) and their refractive properties. The role of refraction in gravitational lensing is exemplified in the case of a microlensing event and a signature of such an effect is discussed.
Highlights
The two most challenging problems in general relativity are: quantization of the gravitational field, as a precondition for unification of gravity with the other three interactions, and application of general relativity to investigation of the Universe
This formalism is capable of handling the whole range of situations, from gravity dominated lensing to refraction dominated lensing; in principle, it applies both to microlensing events and macrolensing images
The microlensing technique was advocated by Paczyński for detecting brown dwarfs in the galactic halo in an attempt to estimate their contribution to the dark matter [12]
Summary
The two most challenging problems in general relativity are: quantization of the gravitational field, as a precondition for unification of gravity with the other three (quantized) interactions, and application of general relativity to investigation of the Universe. One can think of a number of situations, where the total lensing effect is a (possibly nonlinear) superposition of the gravitational component and the refractive one This may occur where the lensing object possesses an extended gaseous envelope, where lensing is caused by a massive molecular cloud, by a gas-rich galaxy, a compact body embedded in the plasma cloud or a compact body that generates strong magnetic field. These situations can be handled with a theory of simultaneous gravitational and refractive lensing.
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