Final answer:
MACHOs are dark matter candidates found through microlensing, making stars appear brighter as MACHOs pass in front. Although some have been discovered, not enough MACHOs have been found to account for all the dark matter in galactic halos.
Step-by-step explanation:
Massive Compact Halo Objects (MACHOs) are potential dark matter candidates that are thought to comprise large, invisible objects such as brown dwarfs, white dwarfs, or black holes. These objects are deemed to reside in galactic halos, areas around galaxies with a significant amount of mass. MACHOs can be detected through a process known as microlensing, where the light from a distant star is magnified as a MACHO passes between the star and Earth, resulting in an apparent increase in the star's brightness for a short period.
Observations have been made in search of MACHOs, such as monitoring millions of stars in galaxies like the Large Magellanic Cloud. Research teams have reported detecting the characteristic brightening caused by microlensing, but the numbers of these MACHOs found are not sufficient to account for the dark matter in our galaxy's halo. Automated telescopes and computer systems aid in this extensive search, but the issue remains: there seem to be too few MACHOs to explain all of the dark matter in the halo of the Milky Way.