Simulation of the explosion of one of the first supernovas. The gray lines in the background are cosmic structures of dark matter. Credit: Asia/Ki-Jung Chen
Using advanced 3D models, astronomers have discovered that the properties of the first galaxies in the universe were largely determined by the masses of the first stars. Qi-Jong Chen (Institute of Astronomy and Astrophysics, Academia Sinica) and his team studied the so-called “cosmic dawn,” the period between 200 and 400 million years after the Big Bang, when the first stars formed—a third population called stars. The radiation from those stars has slowly but surely ended the dark ages of the universe, when there were no sources of light at all, a period that began 380,000 years after the Big Bang. The well-known ΛCDM model of the universe assumes the existence of cold dark matter (CDM), and one theory based on this states that in the early universe there were small halos of dark matter, weighing up to a million solar masses. As a result of these small halos, the first stars were formed, which were very heavy and exploded as supernovae after a short but intense life. But the first stars don't necessarily mean the first galaxies, so the question for Chen and his group was what exactly the connection between the first stars and the first galaxies looked like.
Credit: Asia/Ki-Jung Chen
What is important in the process of forming the first galaxies is that there is a cycle of stars being formed, which develop over time and then new stars are formed, and so on. For such a cycle, it appears that dark matter halos must have a mass of a billion solar masses. Star formation can then begin without losing the supply of cold gas in the intergalactic medium. In addition to dark matter, the gas itself also plays an important role. The interaction between the first stars and their surrounding gas (the so-called “feedback” of those stars) was complex, both in terms of chemistry (tertiary stars were the first providers of heavy elements) and in terms of “mechanics”. . To get a good picture of all this, Chen and his team ran very detailed 3D radiohydrodynamic simulations on computers. This showed that the physical properties of the first galaxies were determined by the mass of the first stars. Supernovae from massive protostars produce more metal, affecting the primordial gas by cooling it and allowing low-mass stars to form. Below you can see parts of that simulation.
Credit: Asia/Meng Yuan Hu
These early galaxies did not have spiral arms like the Milky Way does now, but were irregular in shape. Presumably they didn't rotate either. After the first action of “Pop III” stars, a few hundred to several thousand second-generation stars, Pop II stars, can form in the central regions of galaxies. They want to study the first galaxies using telescopes like Webb.
You can read more about this research in the professional article by Ke-Jung Chen et al, How the third group of supernovae determined the properties of the first galaxies, Astrophysical Journal (2024).
source: Phys.org.
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