Astronomers using NASA's James Webb Space Telescope have uncovered the processes by which stars in their final evolutionary stages generate cosmic dust in environments extremely poor in elements heavier than hydrogen and helium, known in astronomy as metals. The research, led by Claudio Gavetti, a PhD student at Italy's National Institute for Astrophysics and Roma Tre University, was published today in The Astrophysical Journal and offers new observational constraints on how evolved stars form dust under conditions resembling those of the early universe.
The study focused on the dwarf galaxy Sextans A, a cosmic laboratory located on the outskirts of our Local Group. This galaxy is characterized by an exceptionally low metal content, estimated between 1 percent and 7 percent of that of the Sun. This unique composition makes Sextans A very similar to the galaxies that populated the young, primordial universe, providing researchers with a rare opportunity to analyze processes analogous to those occurring billions of years ago.
«Studying directly the galaxies that populated the early universe is still very difficult,» said Claudio Gavetti. «Observing a nearby galaxy like Sextans A, which presents similar chemical conditions, offers us a valuable opportunity to understand how the first generations of stars evolved and what role they played in transforming the interstellar medium.»
By combining ultra-high-resolution observations from JWST's NIRCam and MIRI instruments with advanced theoretical models that couple stellar evolution to dust formation in circumstellar winds, the research team mapped the entire population of stars in the evolutionary phase known as the asymptotic giant branch. This phase represents the final stage of life for low- and intermediate-mass stars, during which they shed their outer layers and produce significant amounts of dust.
«The James Webb Telescope allows us to observe with unprecedented detail environments that until a few years ago were beyond our reach,» explained Flavia Dell'Agli, a researcher at INAF and co-author of the study. «The value of these data lies not only in the images but in the possibility of comparing them with theoretical models and verifying how accurately they describe stellar evolution.»
The results show that the vast majority — over 90 percent — of these giant stars are almost completely devoid of surrounding dust. However, the team identified a subset of twenty stars enveloped in thick dust shells. Analysis revealed that nearly all of these dust factories formed between two and three billion years ago from stars with an initial mass of about one and a half times that of the Sun.
This work represents a decisive step forward in understanding whether and how efficiently giant stars can produce interstellar dust in primordial environments, where raw materials were scarce. The findings are crucial for understanding the present-day universe, as interstellar dust acts as a catalyst for gas cooling, thereby enabling the birth of new generations of stars and planetary systems.
The research provides new insights into the dust enrichment of the early universe, a process that has remained poorly understood due to the difficulty of observing distant galaxies directly. By studying a nearby analog like Sextans A, astronomers can infer the conditions that prevailed in the first galaxies and trace the cycle of matter from stars to the interstellar medium.
The study also highlights the power of JWST to resolve individual stars in nearby galaxies and characterize their properties in detail. The combination of high-resolution imaging and spectroscopic capabilities allows scientists to identify the chemical composition and evolutionary stage of stars that are otherwise too faint or crowded to study with ground-based telescopes.
Future observations with JWST and other facilities are expected to expand this analysis to other metal-poor galaxies, providing a broader view of dust production in the early universe. The team plans to continue investigating the properties of the dust-producing stars in Sextans A and to explore how their findings fit into the larger picture of galaxy evolution and cosmic chemical enrichment.
