Population III Stars: The Search for the First Stars in the Universe
Asher Best • December 23, 2025
Before our Sun was born and galaxies formed, the Universe lit its first fires. Population III stars are theorized to be the first stars formed after the Big Bang, the ancestors of all later generations. Astronomers classify stars into three populations—Populations I, II, and III—based on age and metallicity (the proportion of elements heavier than hydrogen and helium). Population III stars were the oldest and metal-free; Population II stars were metal-poor; and Population I stars, like our Sun, are the youngest and most metal-rich.1 Just as our Sun had a birth, so too did the very first stars.
The First Light
In the immediate aftermath of the Big Bang, the Universe was a roiling soup of electrons, protons, and photons. Once the Universe cooled down, protons, and electrons collided forming neutral hydrogen atoms (a process known as recombination) which allowed photons to roam freely and meant the Universe became transparent to photons. After a few hundred million years, the neutral hydrogen atoms were ionized (the process where electrons are separated from the nuclei of an atom when heat or pressure is applied) once again. This marked the period of the Epoch of Reionization which was a period when the first stars and galaxies formed.1 It is hypothesized that dark matter (an invisible particle that has little to no interaction with other particles but has been detected by its gravitational influence1) played a key role in the formation of Population III stars.
How They Formed
Population III stars formed from pristine gas and are almost entirely composed of hydrogen and helium. Additionally, their size can range anywhere from ten to a hundred, and in some cases a thousand, of solar masses.3 That is ten to a thousand times bigger than our Sun! By comparison, Population III stars were quite massive. The gas clouds of the early Universe are said to have formed in what are known as dark matter halos (or “minihalos” for short).2 Within these minihalos, gas cooled and condensed through a cyclical process: electrons bound to hydrogen atoms, were released again, and in turn triggered further reactions. This chain of interactions ultimately made star formation possible.
Why They Matter
Like everything we know and love in the Universe, Population III stars were subject to a finite lifespan. Most only lived to be a few million years old. This may seem like a long time to us, but on cosmic timescales, this is a rather brief moment in time. These massive stars underwent thermonuclear explosion due to the production and subsequent annihilation of electron-positron pairs in its hot core.3 Gravity forced the core of these stars to collapse once the radiation pressure support was lost and ignited explosive oxygen and silicon resulting in the stars complete disruption.3 This phenomenon is known as pair-instability supernovae (PSNe). The explosions of these stars scattered their chemical enrichment across the galaxy which ultimately led to the formation of the next generation of stars. Had all those stars from the distant past not exploded, the human race and life as we know it would have never existed.
The Search Today
There has been a promising discovery made by the James Webb Telescope (JWST) recently known as the galaxy LAP1-B found in the galaxy cluster MACS J04165, but more evidence is warranted before Population III stars are confirmed to be more than a mere hypothesis. The reason we can even discover galaxies as distant as LAP1-B is due to a process known as gravitational lensing which was predicted by Einstein’s relativity. Gravitational lensing is when massive objects bend spacetime causing the light from distant objects to warp and magnify around them. The stretched and elongated light you see in the image below are distant galaxies captured via this phenomenon.
Peering far enough out into the cosmos and back into time when Population III stars are presumed to have existed is no easy task even with our advances in technology. JWST is able to see up until the formation of the first stars in the far infrared whereas Hubble can only reach just shy of modern galaxy formation in the near infrared.
As the Universe expands, the space between stars and galaxies grows which causes light to stretch to longer wavelengths.4 As a result of these stretched wavelengths of light, these stars are so dim that we would need to locate a cluster of them just to be able to capture enough light produced from these stars.1
Population III stars were the Universe’s first act of creativity, turning raw hydrogen into the building blocks necessary for future complexity. I have hope that our advances in technology and space exploration will lead us to uncovering the origins of these progenitors in the coming years. All the amazing scientists and engineers who created JWST have shown us that with each new technological advancement we are able to peer further back in time and out into the cosmos in hopes of discovering why we are here and where we came from.
References
1First Light: Switching on Stars at the Dawn of Time by Emma Chapman. https://www.amazon.com/First-Light-Switching-Stars-Dawn/dp/1472962923
2The formation of the first stars and galaxies” by Bromm et al., Nature 459, 49–54 (2009). https://arxiv.org/pdf/0905.0929
3The first fireworks: A roadmap to Population III stars during the epoch of reionization through pair-instability supernovae. https://academic.oup.com/mnras/article/527/3/5102/7424186?login=false
4Cosmological Redshift by NASA. https://science.nasa.gov/mission/hubble/science/science-behind-the-discoveries/hubble-cosmological-redshift/
5LAP1-B is the First Observed System Consistent with Theoretical Predictions for Population III Stars. https://iopscience.iop.org/article/10.3847/2041-8213/ae122f/pdf