For generations, astronomers have weighed the cosmos using a single mathematical assumption — that stars are born in the same proportions everywhere, from the densest galactic cores to the quietest cosmic backwaters. Researchers at the University of Missouri, drawing on the Gaia satellite's vast stellar census, have found that this assumption does not hold: different star clusters carry different signatures of mass, shaped by the unique conditions of their birth. The tool astronomers have trusted to fill in what they cannot see — the initial mass function — must now be reimagined not as a univ