Scientists Uncover the Secret Mechanism Behind Galaxy Growth

Galactic evolution is often portrayed as a sequence of catastrophes—titanic collisions and mutual destruction. However, observational data suggest that violent events are the exception rather than the rule. The actual history of the universe is written not in explosions, but in subtle structural shifts, the chemical composition of stars, and relic density fluctuations. A central paradox in modern cosmology emerges from the gap between merger theories and the observed architecture of galaxies. Theoretically, a major collision between two systems of comparable mass should disrupt ordered rotation, transforming a disk into a chaotic elliptical galaxy. Yet, statistics from the local universe show that 73–75% of objects remain spiral galaxies with thin disks, while only 3–5% are elliptical. This suggests that the Milky Way and most of its neighbors grew not through cataclysms, but through the "quiet" absorption of small satellites that lack the mass to destroy the host's disk structure. This process of galactic cannibalism leaves distinct markers. As the gravity of a large system tears apart a dwarf galaxy, its stars are stretched into stellar streams following the original orbit. By analyzing four such streams from the Sagittarius dwarf galaxy, researchers have reconstructed the mass distribution of the Milky Way. The findings reveal that the total mass of our galaxy is ten times greater than the mass of all visible matter—gas, dust, and stars combined.