Astrophysics & Particle Physics-APPC 2026

Population III stars are the earliest generation of stars that have formed in the universe, which came into being some few hundred million years after the Big Bang. They differed from subsequent generations in that they were metal-poor, made up nearly entirely of hydrogen and helium, the elements that existed during primordial Big Bang nucleosynthesis. Their creation initiated the cosmic dawn, finishing the dark ages of the universe and triggering the initial sources of light. These stars were thought to have been hot, massive, and brief, and some weighed more than hundreds of suns. Their strong ultraviolet radiation was instrumental in reionizing the universe, ionizing neutral hydrogen and defining the intergalactic medium. As Population III stars exploded as supernovae, they enriched their environments with the first heavy elements (metals) seeding Population II star and early galaxy formation.

Direct observation of Population III stars is very difficult since they lived at high redshifts (z > 10) and have since vanished. Rather, astronomers examine their indirect signatures using metal-poor stars in the Milky Way halo, early galaxy spectra, and nucleosynthetic yields based on simulations. The James Webb Space Telescope (JWST) and future observatories will be able to detect their impact on the first galaxies and cosmic structures.By examining these original stars, astronomers are able to understand the early processes of stellar evolution, galaxy formation, and the workings that built the observable universe. Population III stars are therefore a central piece in deciphering the timeline of the universe, filling the gap between the Big Bang and galaxy formation.