The assumption at the center of the study is known as the stellar initial mass function, or IMF. Gaia has created an extraordinarily detailed map of the Milky Way, measuring the positions, motions and other properties of nearly two billion stars. The researchers emphasize that additional observations and independent analyses will be needed to establish how broadly the relationship applies beyond the Milky Way. The study, titled “Direct evidence for stellar initial mass function variation in the Milky Way,” was published in The Astrophysical Journal Letters. Subject of Research: Stellar formation environments and variation in the stellar initial mass function across Milky Way star clusters.