In a new article published Wednesday in the magazine natureastronomers Maosheng Xiang and Hans-Walter Rix, of the Max Planck Institute astronomya study used nearly a quarter of a million stars For the timing of the evolution of the Milky Way, based on current knowledge of stellar life cycles for a better understanding of the galactic longer life cycle.
The spiral disk of the Milky Way can be divided into two groups, the thin inner disk of young stars to which our Sun belongs, and the somewhat thicker and older disk of stars that extend beyond the plane of the galactic spiral. Around the galaxy in general there is also a halo, which is a scattered group of older stars.
Xiang and Six found that the thick disk probably began forming about 13 billion years ago, or 800 million years after the Big Bang, while the inner galactic halo formed about two billion years later. The inner halo was assembled by the ancient merger of the Milky Way with the Gaia-Enceladus galaxy, a dwarf galaxy that mostly merged with our own between 8 and 11 billion years ago.
To make this discovery, the researchers used stellar clocks: low-mass stars in the “giant” phase. When a low-mass star, like the Sun, begins to run out of hydrogen, its core contracts as a kind of counterweight to its gravitational pressure pushing it toward collapse. Later, the hydrogen surrounding the star will ignite and enter the star into the giant phase, but as long as it is giant, the luminosity of the star is closely related to its age.
Unfortunately, stars only spend a few million years in the sub-giant phase, so a massive survey of the stars is required to find enough of them to yield useful data. Xiang and six used data from China’s LAMOST (Large Celestial Region Multi-Object Fiber Spectroscopic Telescope) and the GAIA (Global Astrophysical Astrophysical Interferometer) spacecraft from European Space Agencyto study 247,104 giant stars ranging in age from 15 billion to 13.8 billion years.
The results, when combined with future surveys using the same technology, could help astronomers better understand how galaxies formed, how our galaxy formed, and how we came here to think about any of these questions.
“With an innovative approach to estimating birth dates for stars, Chiang and Rex have been able to help us better understand how our galaxy formed,” University of Notre Dame physicist Timothy Beers wrote in a commentary that also appeared. nature Wednesday.
“And this approach is scalable, which means that as data becomes available for larger samples of stars in the Milky Way, this picture will become clearer.”
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