massive astrophysical compact halo object

Component of the Galaxy's dark matter. Most MACHOs are believed to be brown dwarfs, tiny failed stars with a mass of about 8% that of the Sun, but they may also include neutron stars left behind after supernova explosions. MACHOs are identifiable when they move in front of stars causing microlensing (magnification) of the star's light. Astronomers first identified MACHOs in 1993 but it is highly uncertain what fraction of dark matter they constitute.