A great mystery: physicists have discovered why the first stars in the universe couldn't grow indefinitely.

Several hundred million years after the Big Bang, the first stars emerged in the universe, known as Population III stars. Interestingly, the Sun, which formed 9 billion years after the Big Bang, belongs to Population I stars. The first stars were massive, although their mass is believed to have been limited to several tens of solar masses. They were extremely bright and lived only a few million years, ending their life cycle with the explosion of the very first supernovae. It was these explosions that filled the universe with the first heavy chemical elements. The exact reason why the first stars could not grow indefinitely remains unclear. However, the authors of a study published on the arXiv preprint server proposed their version of events, as reported by Universe Today.

It is now known that modern stars form from a cloud of cold molecular hydrogen, which collapses under gravity to create a protostar surrounded by a gas disk. Protostars draw material from these disks for their growth and mass accumulation.

As stars accumulate mass, they heat up, and this heat warms the surrounding disk. This can slow down or limit the growth of the stars. Additionally, newborn stars emit powerful radiation that can disperse nearby gas, which is essential for their continued growth. Protostars also rotate much faster than ordinary stars, creating strong magnetic fields that can further restrict stellar growth.

But did similar processes occur in the early universe concerning the very first stars? It was previously assumed that Population III stars could accumulate any mass, but later studies revealed that their mass was indeed limited.

Astrophysicists created simulations that incorporated the strong radiation and magnetic fields of the first stars to determine what might have limited their growth and mass accumulation. The research indicated that the first stars could not have a mass exceeding 65 times that of the Sun. Scientists believe that the primary factor in limiting the growth of the first stars was their magnetic fields.

According to the simulations, as the first stars accumulated mass, their gravity increased, which should have led to the accumulation of even more gas. However, at that time, the magnetic fields counteracted gravity, coming into play even before the powerful radiation from the young stars caused the surrounding gas to disperse.

This means that the growth of the first stars was initially slowed by the influence of magnetic fields, and then completely halted due to the impact of their radiation on the surrounding gas disk. Ultimately, this disk lacked sufficient material for the further growth of the first stars.

Testing this theory is extremely challenging, as scientists have never directly observed the very first stars, leaving many aspects of their nature a mystery.