Far out cosmology: birth and aging of the Milky Way (Introduction)

by David Turell , Thursday, April 07, 2022, 14:34 (959 days ago) @ David Turell

Our galaxy is huge and appeared quickly after the Big Bang:

https://www.nature.com/articles/s41586-022-04496-5

"The formation of our Milky Way can be split up qualitatively into different phases that resulted in its structurally different stellar populations: the halo and the disk components. Revealing a quantitative overall picture of our Galaxy’s assembly requires a large sample of stars with very precise ages. Here we report an analysis of such a sample using subgiant stars. We find that the stellar age–metallicity distribution p(τ, [Fe/H]) splits into two almost disjoint parts, separated at age τ ≃ 8 Gyr. The younger part reflects a late phase of dynamically quiescent Galactic disk formation with manifest evidence for stellar radial orbit migration4,5,6; the other part reflects the earlier phase, when the stellar halo7 and the old α-process-enhanced (thick) disk, formed. Our results indicate that the formation of the Galaxy’s old (thick) disk started approximately 13 Gyr ago, only 0.8 Gyr after the Big Bang, and 2 Gyr earlier than the final assembly of the inner Galactic halo. Most of these stars formed around 11 Gyr ago, when the Gaia-Sausage-Enceladus satellite merged with our Galaxy10,11. Over the next 5–6 Gyr, the Galaxy experienced continuous chemical element enrichment, ultimately by a factor of 10, while the star-forming gas managed to stay well mixed." (my bold)

Commentary by experts:

"Intagliata: Now Rix and a colleague at the Max-Planck Institute for Astronomy in Germany have indeed gone star by star… determining the ages of nearly a quarter million stars in the Milky Way. That work has allowed them to reconstruct some of the major life events in the galaxy's evolution, over its 13 billion years of existence.

"Rix: What it showed is that indeed the youth and childhood of the Milky Way was turbulent… but actually afterwards we've lived an enormously sheltered life compared to most other galaxies. Gas drizzled in, and the suburbs grew peacefully and sprawled. (my bold)

"Hans-Walter Rix: There were glory days, there were disasters, and all of these things kind of happen in the life of galaxies. And the Milky Way is just the one galaxy where we can look at star by star so you can kind of see individual episodes in actual detail.

"Intagliata: The astronomers say that the galaxy's thick disk began to form about 13 billion years ago, just 800 million years after the Big Bang. Then, around 11 billion years ago, a cataclysmic collision occurred: the Gaia-Enceladus satellite galaxy crashed into the Milky Way. (my bold)

"Rix: And just at the same time, there was a huge burst of star formation, or a large increase of star formation in our own Milky Way. And that suggests—doesn't prove—that the perturbance that this in-falling satellite created, caused a lot of gas that was in our Milky Way to form stars."

My comment: Seems like God was carefully supervising how the Milky Way formed soon after the Big bang. Like our privileged planet, a privileged galaxy.