Scientists believe 99.9 percent of this galaxy is dark matter. This distribution suggests that, despite its low light, the galaxy is a gravitationally bound system, implying a particularly dense dark matter halo. According to current models, dark matter constitutes roughly 27 percent of the universe’s total energy density and about 85 percent of its matter. For example, current models indicate that our galaxy is embedded in a halo composed of about 90 percent dark matter. Beyond their rarity, scientists value them because they serve as natural laboratories for exploring the nature of dark matter and testing current models of galaxy formation.