RUI: Statistical Modeling of Microlens Masses

University Of Hawaii At Hilo, Hilo HI

Investigators

Abstract

AST-0205754 Heacox Dr. William Heacox will analyze gravitational microlens survey data in the current literature in order to deduce the mass distributions of the objects causing the lensing, and thus help characterize their natures. Microlensing is a promising means of detecting otherwise undetectable planetary- to stellar-mass objects in such locations as the halo of our galaxy, where a large amount of dark matter of unknown nature is known to exist. In a typical microlens survey, a few million stars in the Large Magellanic Cloud are monitored periodically to detect the optical amplification caused by gravitational lensing when a Galactic halo object (the lens) passes nearly in front of a background star (the source). While the resulting amplification amplitude depends upon lens mass, it also depends upon such unknowable quantities as the relative velocity of lens and source, and the distance of closest encounter of the lens to the line-of-sight to the source. This complication has prevented accurate estimates of lens masses, so that the observation of a few tens of microlenses has not greatly aided in the identification of halo dark matter. Dr. Heacox' research consists of the application of sophisticated statistical modeling techniques to the entire set of observed microlenses in a survey, in order to determine the statistical distribution of lens masses (rather than the masses of individual lenses). The method uses all that is knowable about the kinematics (velocities, distances) of lens and source populations, together with the set of observed microlens parameters, to infer all that can be deduced about the mass distribution of the underlying population causing the lensing. In application to the Galactic halo microlenses, the result should be the first credible estimate of the mass distribution of the halo dark matter, and a concomitant increase in our understanding of the nature of this material. The nature of dark matter in the Universe is one of the outstanding problems in modern astronomy; a better understanding of the component in our galaxy will be a useful first step in determining what most of the Universe is made of. This award is made under the auspices of the Research in Undergraduate Institutions (RUI) program at NSF. ***