Boson Stars as Gravitational Lenses

Abstract

We discuss boson stars as possible gravitational lenses and study the lensing e †ect of these objects made up of scalar particles. The mass and the size of a boson star may vary from an individual Newtonian object similar to the Sun to the general relativistic size and mass of a galaxy close to its Schwarzschild radius. We assume boson stars to be transparent, which allows the light to pass through them, although the light is gravitationally deÑected. We assume boson stars of mass M \ 1010 to be on M _ noncosmological distance from the observer. We discuss the lens equation for these stars as well as the details of magniÐcation. We Ðnd that there are typically three images of a star, but the deÑection angles may vary from arcseconds to even degrees. There is one tangential critical curve (Einstein ring) and one radial critical curve for tangential and radial magniÐcation, respectively. Moreover, the deÑection angles for the light passing through the gravitational Ðeld of boson stars can be very large (even of the order of degrees), which reÑects the fact that they are very strong relativistic objects. We derive a suitable formula for the lens equation for such large deÑection angles. Although the large deÑection angle images are highly demagniÐed, their existence in the area of the tangential critical curve may help with observational detection of suitable lenses possessing characteristic features of boson stars, which could also serve as a direct evidence for scalar Ðelds in the universe.

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