Black hole, neutron star and white dwarf candidates from microlensing with OGLE-III

Abstract

Most stellar remnants so far have been found in binary systems, where they\ninteract with matter from their companions. Isolated neutron stars and black\nholes are difficult to find as they are dark, yet they are predicted to exist\nin our Galaxy in vast numbers.\n We explored the OGLE-III database of 150 million objects observed in years\n2001-2009 and found 59 microlensing events exhibiting a parallax effect due to\nthe Earth's motion around the Sun. Combining parallax and brightness\nmeasurements from microlensing light curves with expected proper motions in the\nMilky Way, we identified 13 microlensing events which are consistent with\nhaving a white dwarf, neutron star or a black hole lens and we estimated their\nmasses and distances. The most massive of our black hole candidates has 9.3\nMSun and is at a distance of 2.4 kpc. The distribution of masses of our\ncandidates indicates a continuum in mass distribution with no mass gap between\nneutron stars and black holes. We also present predictions on how such events\nwill be observed by the astrometric Gaia mission.\n