Line of sight paraxial gravitational cloaking

Abstract

Three-dimensional gravitational cloaking is known to require exotic matter and energy sources, which makes it arguably physically unrealizable. On the other hand, typical astronomical observations are performed using one-dimensional paraxial line of sight geometries. We demonstrate that unidirectional line of sight gravitational cloaking does not require exotic matter, and it may occur in multiple natural astronomical scenarios which involve gravitational lensing. In particular, recently discovered double gravitational lens SDSSJ0946+1006 together with the Milky Way appear to form a natural paraxial cloak. A natural question to ask, then, is how much matter in the universe may be hidden from view by such natural gravitational cloaks. It is estimated that the total volume hidden from an observer by gravitational cloaking may reach about 1% of the total volume of the visible universe.