Primordial Star Formation in Early Universe

The formation of the first, or Population III, stars marked a pivotal epoch in cosmic history. Emerging in dark matter minihalos at redshifts of around 20–30, these metal-free objects arose from the collapse of primordial gas cooled primarily by molecular hydrogen. The efficiency of H₂ cooling dictated when and where dense gas clumps could form, leading to fragmentation into protostellar cores. Simulations suggest a characteristic mass distribution skewed towards tens to hundreds of solar masses, although multiplicity in protostellar discs may produce lower-mass companions. Radiative and chemical feedback from the earliest stars regulated subsequent star formation, reionised the intergalactic medium and seeded it with the first heavy elements. The eventual supernovae of massive Population III stars injected kinetic energy and nucleosynthetic products, influencing the initial mass function of later generations. Observational constraints remain challenging: direct detection of primordial stars is beyond current capabilities, but indirect probes—such as metal-poor stellar archaeology, the global 21-cm signal and gravitational waves—offer promising avenues. Understanding primordial star formation is essential for reconstructing the dawn of galaxies, the assembly of supermassive black hole seeds and the early chemical enrichment of the Universe.

Research from Nature Portfolio

Recent work has identified a clear chemical signature of a very massive primordial star in a surviving, extremely metal-poor halo star. Unusual abundance ratios among sodium, magnesium and iron-peak elements are consistent with enrichment by a pair-instability supernova (PISN) from a progenitor exceeding 140 solar masses. This finding provides the most direct evidence to date for the existence of very massive Population III stars, supporting theoretical predictions of PISN yields and their role in early chemical evolution.

Primordial Star Formation in Early Universe publication trend

The graph below shows the total number of articles in primordial star formation in early universe across all publications each year (not limited to Nature Index journals).

Technical terms

Molecular hydrogen cooling (H₂ cooling): Radiative process by which H₂ molecules emit energy and enable gas to cool and condense in metal-free environments.

Dark matter minihalo: A low-mass dark matter concentration (10⁵–10⁶ M☉) that provides the gravitational potential well for primordial gas collapse.

Population III stars (Pop III): The first generation of stars, formed from pristine hydrogen and helium without heavier elements (metals).

Pair-instability supernova (PISN): A thermonuclear explosion of a very massive star (≈140–260 M☉) driven by electron–positron pair production in its core.

Initial mass function (IMF): The distribution of stellar masses at birth in a given star-forming region.

Radiative feedback: Influence of stellar radiation on surrounding gas, affecting its temperature, ionisation state and ability to form new stars.

References

1. A metal-poor star with abundances from a pair-instability supernova. Nature (2023).
2. The First Stars: Formation, Properties, and Impact. Annual Review of Astronomy and Astrophysics (2023).
3. True Pair-instability Supernova Descendant: Implications for the First Stars’ Mass Distribution. The Astrophysical Journal Letters (2024).
4. Impact of radiative feedback on the initial mass function of metal-poor stars. Monthly Notices of the Royal Astronomical Society (2024).