The first stars in the universe, known as Population III stars, likely possessed a far more diverse mass range than previously theorized. New hydrodynamical simulations indicate that supersonic turbulence within primordial dark matter halos disrupted the formation of monolithic, super-massive stellar bodies.
Meng-Yuan Ho, a researcher at the Institute of Astronomy and Astrophysics at Academia Sinica, led the study published in The Astrophysical Journal. The team utilized the Illustris TNG simulation suite to model the assembly of 15 primordial minihalos.
By increasing the resolution by a factor of 100,000, the researchers tracked gas movements on scales smaller than one light year. This high-resolution approach was essential for capturing the complex, multi-scale interactions of gas as it settled into the gravitational potential wells of dark matter.
This granular approach allowed the team to observe the emergence of strong turbulent flows within the pristine gas clouds. These clouds, composed primarily of hydrogen and helium, lacked the metal-line cooling mechanisms that regulate star formation in the modern universe. The simulations began when the universe was approximately 300 million years old, providing a window into the earliest stages of structure formation.
Standard theoretical models previously suggested that the absence of heavy elements resulted in significantly higher Jeans masses, forcing the formation of massive stars ranging from 40 to 500 solar masses. The new data suggests that the environment was not the calm, serene setting once envisioned by astrophysicists. Instead, gas flowed into minihalos through multiple streams, colliding at the center to generate intense, chaotic motion.
The researchers found that this turbulence fragmented the gas into smaller, distinct clumps rather than allowing a singular, massive collapse. The simulations tracked gas velocities reaching 1.8 to 4.2 times the speed of sound. These supersonic flows created clumpy structures within the minihalos, with individual clumps exhibiting masses as low as 2.6 solar masses.
This fragmentation process directly challenges the assumption that Population III stars were uniformly massive. The resulting mass distribution is now estimated to span from 10 to the power of negative 3 to 10 squared solar masses. This wide variance suggests that the initial mass function of the first stars was far more complex than earlier, lower-resolution models indicated.
This research addresses a persistent discrepancy regarding the chemical signatures observed in ancient stars within the Milky Way. If the first generation of stars had been exclusively massive, their subsequent supernovae would have enriched the interstellar medium with metals more rapidly than observed. The presence of low-metallicity stars in the local universe suggests that their ancestors were not as massive as early models predicted.
Turbulence provides a mechanism that accounts for this lower-than-expected enrichment, as smaller stars produce less intense feedback and disperse fewer heavy elements. By producing a population of smaller stars, the turbulent environment effectively lowered the average chemical yield of the first stellar generation. This finding aligns the theoretical models of the early universe with the observed chemical compositions of the oldest stars currently detectable in our galaxy.
The findings clarify how the first stars influenced the development of early galaxies through stellar feedback. Smaller stars exert less radiative pressure on their surroundings, which alters the rate at which subsequent generations of stars can form. This feedback loop is a critical factor in understanding the transition from the dark ages to the emergence of structured galaxies.
Future investigations will likely focus on how these turbulent processes scale across larger dark matter structures. Researchers aim to refine the initial mass function of these primordial objects to better align with current observational data from deep-space surveys. These upcoming milestones will be essential for mapping the evolution of the early universe with greater precision.
