The process of formation of the Milky Way can be divided into qualitatively different phases, which resulted in the emergence of stellar components that differ from each other in terms of structure: the components of the corona and the stellar disk. Revealing a quantitative comprehensive picture of the assembly of our galaxy requires a large sample of stars with very precisely defined ages.
In this published paper, the researchers benefit from conducting an analysis of a sample that fulfills the aforementioned trait. The researchers found that the correlation distribution between stellar age and the mineral composition of the star, which is expressed as p(τ,
[Fe/H]), splits into two semi-separate parts, which separate after about 8 billion years. The smaller portion reflects a later phase in the formation of a dormant galactic disk, with clear evidence of radial-stellar orbit transition; The other part reflects the early phase, when the stellar halo and the old (thick) disk, enhanced by the so-called “alpha” process, were formed.
The researchers’ findings indicate that the formation of the ancient (thick) galactic disk began about 13 billion years ago, just 0.8 billion years after the Big Bang, and two billion years before the final assembly of the inner galactic halo. It turns out that most of these stars were formed about 11 billion years ago, when the Gaia-Sausage-Enceladus galaxy merged with our galaxy. Over a subsequent period of 5-6 billion years, the galaxy experienced a continuous enrichment of its chemical elements, eventually increasing in amount by about 10 times, while the star-forming gas remained largely mixed.