Gravitational lensing as a probe of compact object populations in the Galaxy

¹ Astronomical Observatory, Warsaw University, Aleje Ujazdowskie 4, 00478 Warsaw, Poland e-mail: tb@astrouw.edu.pl
² Nicolaus Copernicus Astronomical Center, Bartycka 18, 00716 Warsaw, Poland
³ Department of Astronomy, New Mexico State University, Frenger Mall, Las Cruces, NM, USA

Received: 23 November 2006
Accepted: 4 October 2007

Abstract

Aims.The population of solitary compact objects in the Galaxy is very difficult to investigate. In this paper we examine the possibility of using microlensing searches to detect and to analyze the properties of solitary black holes and neutron stars.

Methods.Evolution of single and binary stars is followed using the StarTrack population synthesis code. The spatial distribution of compact objects in the Galaxy is determined by propagating them in the Galactic gravitational potential. Lensing events are found by tracing individual stars and compact objects.

Results.We find that compact object lensing events are concentrated in a region with a radius of 5 degrees around the Galactic center. The distribution of masses of the lenses for the models we consider differs, but only slightly, from the underlying mass distribution of compact objects. The expected detection rates are of the order of a few per year.