Scientists now know the exact age of our galaxydating the formation of some parts of the Milky Way in just 800 million years following the Big Bang.
In a new article published Wednesday in the journal Naturethe astronomers Maosheng Xiang and Hans-Walter Rix, from the Max-Planck Institute of Astronomyused a study of almost a quarter of a million stars to time the development of the Milky Way, building on existing knowledge of stellar life cycles to better understand the longest galactic life cycle.
The Milky Way’s spiral disk can be divided into two populations, the thin, inner disk of younger stars, to which our Sun belongs, and a thick, somewhat older disk of stars that extend beyond the plane of the galactic spiral. . Around the galaxy in general is also the halo, a sparse population of older stars.
Xiang and Six found that the thick disk probably began to form regarding 13 billion years ago, or 800 million years following the Big Bang, while the inner galactic halo formed regarding two billion years later. The assembly of the inner halo took place through the ancient merger of the Milky Way with the Gaia-Enceladus galaxy, a dwarf galaxy that merged for the most part with our galaxy between 8 and 11 billion years ago.
To make the discovery, the researchers used stellar clocks: low-mass stars in the “subgiant” phase. When a low-mass star, like the Sun, begins to run out of hydrogen, its core contracts as a kind of counterweight to the pressure of its own gravity that pushes it toward collapse. Later, the hydrogen surrounding the star will ignite and cause the star to enter the giant phase, but as long as it is subgiant, the luminosity of the star is closely related to its age.
Unfortunately, stars only spend a few million years in the subgiant phase, so a massive survey of stars is needed to find enough of them to yield useful data. So Xiang and Six used data from LAMOST (Large Celestial Area Fiber Multi-Object Spectroscopic Telescope) in China and the GAIA (Global Astrometric Interferometer for Astrophysics) spacecraft, European Space Agencyto study 247,104 subgiant stars ranging in age from 15 billion to 13.8 billion years.
The results, when combined with future surveys using the same technique, might help astronomers better understand how galaxies form, how our galaxy formed, and how we came to be here to ponder any of these questions.
“With an innovative approach to estimating the birth dates of stars, Xiang and Rix have been able to help us better understand how our galaxy formed,” wrote University of Notre Dame physicist Timothy Beers in a comment that also appears. on Nature on Wednesday.
“And the approach is scalable, which means that as data become available for larger samples of stars in the Milky Way, this image will get even sharper.”
