About 90% of the entire mass of the milky way is thought to consist of dark matter.

The nature of this dark halo is completely unknown, and the microlensing experiment was designed to resolve this question by monitoring background stars in our nearest neighbour galaxies, the Megellanic Clouds. There are a lot of lensing events from objects about half the mass of the sun, thought to be white dwarfs.

Nature/ volume 394/27^th August 1998, p. 825.