Stellar Chefs: How Ancient Galaxies Brewed Nitrogen ✛
13 billion years ago, in tiny galaxies, the first massive stars ignited. Their light, traveling through the expanding universe, stretched and reddened: this effect helps determine distance. Along the way, the beam passed by a massive cluster of galaxies, whose gravity distorted and magnified it many times over, like a giant lens. The James Webb Space Telescope caught this magnified light and split it into a spectrum (a colorful band). In the spectrum, bright lines from different chemical elements appear: this is spectroscopy, the method of studying composition through light.
Astronomers collected data on 405 such distant galaxies. Individually, they are very dim, so scientists stacked their light, grouping them by stellar mass (total weight of stars). In the average picture, an unexpected chemical pattern emerged: nitrogen was far more abundant than expected, especially in hot regions. The proportion of elements heavier than helium, metallicity, in the smallest galaxies was only 2% of the solar value. This suggests that early supernovae blew away some material, preventing the accumulation of heavy elements.
Where did the excess nitrogen come from? Back in the mid-20th century, Margaret Burbidge, Fred Hoyle, and Hans Bethe explained how stars serve as element factories: in their cores, carbon and oxygen turn into nitrogen. In massive stars at the Wolf-Rayet stage, this process is especially vigorous. Powerful stellar winds expel the cooked nitrogen into space. To explain the observed emission, each such galaxy would have needed about 1650 of these 'chefs' working simultaneously. Their combined efforts would be enough to enrich an entire globular cluster — a dense swarm of hundreds of thousands of stars that still orbits many galaxies today.
The chemical pattern (low carbon, high nitrogen, neon like the Sun) matches exactly what astronomers see in stars of modern globular clusters. So the ancient galactic 'kitchens' prepared the ingredients for future generations of stars. Light that traveled for 13 billion years has brought us their recipes.
Gravitational lensing by the cluster MACS J0416 amplified the light of some galaxies by a factor of 100 — without this natural telescope, they would have remained invisible.
In Arthur C. Clarke’s novel “Blinding Darkness”, aliens eliminate stars to prevent their collapse into black holes. Here, we see stars doing the opposite — scattering life’s elements into space — and it’s this generosity that enables the chemical diversity of galaxies.