A new analysis of almost a quarter of a million stars has clarified a little more the most transcendental pages of the history of the life of our galaxy.
Using data from ESA’s Gaia mission, which calculated the position and motion of 1.5 billion stars, in addition to the Large Sky Area Multi-Object Fiber Spectroscopic Telescope in China, which has measured the chemical composition of 9 million stars, astronomers have shown that a part of the Milky Way known as the “thick disk” began to form 13 billion years ago, about 2 billion years earlier than expected and only 800 million years after the Big Bang.
“Now we can provide a very clear timeline of what happened in the early days of our Milky Way,” says astronomer Maosheng Xiang, leader of the work published in the journal Nature.
In this way, part of our galaxy would be much older than previously believed . The spiral disk of our galaxy can be divided into two: the thin inner disk of younger, bluer stars, to which our sun belongs, and a thick disk that includes somewhat older, red, stars that extend beyond the plane of the galactic spiral (the thick disk is flattened, 100,000 light-years wide and 6,000 light-years thick).
Our galaxy is currently quite cold but its past was diametrically different, being a chaotic place full of activity.
Based on the observations in this study, the thick disk had a very specific peak in star formation about 11 billion years ago; an event that could be related to the merger between the Milky Way and Gaia’s Sausage, a dwarf galaxy of the Milky Way.
a very old star
Astronomers have come to this conclusion after discovering what appears to be one of the oldest stars ever found in the universe. It is small, it has very little metal, which indicates that it was born just after the Big Bang, and it is found in the Milky Way.
The universe was born almost exclusively with hydrogen and helium, while the other chemical elements, known to astronomers as metals, form inside stars. They are returned to space at the end of a star’s life, where they can be incorporated into the next generation of stars. This means that older stars have fewer metals and are said to have lower metallicity.
As a curiosity, our star would therefore be a newcomer to our galaxy, since it is estimated that our Sun is around 4.6 billion years old (and that in about 10 billion years it will die, taking the Earth with it in the future). process).
How does an astronomer date the age of a star?
They rely on models to help them estimate how stars evolve and change over time. When scientists first observe a star, they look for the best model that fits the data, based on its age and composition. The temperatures and luminosities of these stars reveal their ages, allowing researchers to trace how different epochs in galactic history generated stars with different chemical compositions and orbits around the center of the Milky Way. There are approximately 250 billion stars in our galaxy.
If the Milky Way’s thick disk already existed 13 billion years ago and the universe some 13.7 billion years ago, it means that the new James Webb Space Telescope , soon to be ready for full-throttle operation , can discern similar disks in galaxies. 13 billion light years from Earth.
Referencia: M. Xiang and H.-W. Rix. A time-resolved picture of our Milky Way’s early formation history. Nature. Published online March 23, 2022. doi: 10.1038/s41586-022-04496-5.
ESA/Gaia/DPAC; CC BY-SA 3.0 IGO. Acknowledgement: A. Moitinho.