Astrometric microlensing with Gaia

One by-product of the Gaia mission will be a unique inventory of the mass of objects in the solar neighbourhood, irrespective of their luminosity, by way of microlensing. The astrometric microlensing signal measured by Gaia will be sensitive to local populations (within ~ 1 kpc of the Sun) of even the dimmest stars and other dark objects such as isolated neutron stars and black holes.

Simulations by Belokurov & Evans (2002) suggest that ~ 25000 sources will exhibit microlensing events during the 5 years of Gaia's mission. About 10 per cent of these will be of such high quality that the mass of the lens will be recovered with good accuracy.

Gaia measures the small deviation of the centroid of the two images (from a microlensed event) around the trajectory of the source. The image above simulates an astrometric microlensing event as observed by Gaia. Data points include typical sampling astrometric errors for Gaia. The theoretical trajectories of the source are shown with (blue line) and without (red line) the event. The astrometric deviations at the beginning (inset: top left) and the maximum of the event (inset: bottom right) can be clearly detected by Gaia.

Image from Five years at the Movies, N.W. Evans & V.Belokurov, in Proceedings of the Third Sakharov Conference, 2002, eds A. Semikhatov et al., (Scientific World, Moscow).

[Published: 24/11/2003 ]