The Galactic Family Tree: How Star Chemistry Tells the Story express
A star inherits the chemical makeup of its parent gas cloud, just like a child inherits genes from its parents. Astronomers turned this into a method: by measuring the fraction of carbon and other elements with spectroscopy (splitting light into colors), they construct family trees for the stars in a galaxy. It’s like genealogy, but instead of DNA, you’re tracing chemistry.
In the center of the Milky Way, gas poured in stormy streams, stars were born rapidly, and enriched by supernova explosions. Their tree is a tangled bush with short, thick branches. On the outskirts, shaped by spiral arms, the process was smooth: the tree grew with thin, long, symmetrical branches.
This chemical pedigree acts as a time machine for galaxies. By studying these “fossils,” we read the history of bursts and stellar winds, reconstructing the growth of our own Galaxy.
Original abstract
as written by the authors arXiv:2604.11974
Phylogenetic methods, traditionally used in biology to trace the evolutionary relationships among species, are emerging as a powerful framework to reconstruct evolutionary processes in galaxies from chemical information. We apply galactic phylogenetics to study the chemical evolution of stellar populations in distinct regions of a simulated disc galaxy, assessing its capability to unveil assembly histories. We used a high-resolution simulation that follows the chemical enrichment of an isolated disc galaxy, by different stellar progenitors. We track gas particles as they turn into stars and inherit their parent gas chemical composition. Target particles are selected to store the chemical history of each chemical element considered in the simulation. Two regions were analysed: an inner ring, influenced by early bar-driven inflows, and an outer ring, shaped by spiral arms. We built phylogenetic trees for stellar populations in each region and quantified their structure using the Corrected Colless index, a standard metric of tree balance used in biology. The inner ring tree reveals a compact clade of old stars enriched by rapid SNII feedback, followed by a hierarchical sequence with increasing SNIa and AGB contributions. In contrast, the outer ring exhibits more symmetric, caterpillar-like trees with smoother abundance gradients, consistent with more prolonged star formation and efficient local mixing. Chemical enrichment rates corroborate these trends, showing fast early enrichment in the inner ring and gradual, spatially extended enrichment in the outer disc. The structural indices differ significantly between the two regions and converge robustly even for modest stellar samples (NSSP = 100). Galactic phylogenetics provides a novel and complementary tool to decode the fossil record of galaxies.
Some of the Milky Way’s oldest stars contain almost no heavy elements, as if frozen in the era of the early Universe.