Why did the very first stars in the universe require vastly greater initial masses than modern Sun-like stars?
They lacked cooling elements like carbon and oxygen.
The efficiency of cooling dictates how easily gravity can overcome thermal resistance. Modern molecular clouds contain chemically complex elements, such as carbon monoxide, which effectively radiate heat away, allowing the cloud to cool efficiently even at lower masses. The very first stars, however, formed from gas clouds composed only of the primordial elements, lacking these essential cooling agents like carbon and oxygen. Without these effective radiative brakes, the internal thermal pressure was much harder to dissipate. Consequently, for gravity to achieve dominance and initiate collapse in these pristine environments, the initial cloud mass needed to be vastly greater compared to the molecular clouds that form stars similar to our Sun today.
