MACHOs could well be white dwarfs--overturning a common belief that the dark matter would consist mainly of lighter interstellar garbage such as brown dwarfs.

ECONOMIST: The dark side of cosmology

The first kind, the chunks, could be anything in size from dust grains, up through rocks and asteroids, to brown dwarfs (condensed lumps of gas not quite heavy enough to be stars).

ECONOMIST: The dark side of cosmology

The problem is that brown dwarfs have been discovered orbiting other stars, and it is thought that planets can sometimes be ejected from their natal solar systems as a result of gravitational interactions, and may thus be found drifting in space.

ECONOMIST: Twinkle, twinkle, giant planet