Short for MAssive Compact Halo Objects, MACHOs could exist in huge numbers in vast halos surrounding galaxies. In the past few years, astronomers have detected several examples of MACHO-like objects in our galaxy, though not yet enough to account for all the dark matter known to reside there. Brown dwarfs, with a size between normal stars and planets, could be one type of MACHO. These objects form like stars but don't have enough mass to begin the nuclear fusion reactions that cause stars to shine brightly. Other candidate MACHOs include planets, about a dozen of which have been discovered outside our own solar system in the past couple of years, and the halo objects that have recently been detected as they magnify and distort the light from stars in nearby galaxies.

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