A new approach to gravitational microlensing - Time delays and the galactic mass distribution

Abstract

Gravitational lensing of distant sources by massivecompact objects such as stars produces multiple images which aretoo closely spaced to resolve. The combined image can be magnifiedhowever, resulting in an increase in apparent luminosity. This has beenthought to be the sole signature for such 'microlensing' events. Here,a new signature is proposed which may be more sensitive and couldgive an unambiguous determination of the mass of the lensing object,independent of its distance. A time delay between the superposed images onthe order of microseconds to milliseconds will occur for lensing byobjects in the Galaxy. This might be measurable in sources such asradio pulsars, some stars, and perhaps even supernovae. Microlensingprobabilities are calculated from objects in the Galactic disk and bulge, andalso halo objects such as massive stars or large black holes whichmay contribute significantly to the dark matter in the Galaxy. Itis suggested that a study of such time delays could resolve manyfeatures of the mass distribution of luminous and dark matter in theGalaxy and might even provide new tests of general relativity.