Using data from the European Space Agency (ESA) mission Gaia, astronomers have shown that part of the Milky Way, known as the Thick Disc, formed 13 million years ago, about two billion years earlier than previously thought, or the Big Bang. Just 800 million years later.
Researchers at the Max Planck Institute for Astronomy in Germany have taken brightness and position data from Gaia data and compared them to the chemical composition of stars, which the Chinese telescope LAMOST measured at about 250,000 stars. The age of the star can also be determined based on its chemical composition.
Researchers have chosen to study subgiant stars. In the nucleus of these stars, the production of energy is stopped and displaced to the membrane around the nucleus. The star itself is in the process of transitioning to the red giant phase. Since the phase of a subgiant is relatively short in a star’s life cycle, it is possible to determine the age of a star with great accuracy, but it is still quite difficult to calculate.
How old are the stars?
The age of the star is one of the most difficult parameters to determine. It is impossible to measure directly and this is done by comparing the characteristics of the star and stellar evolution with computer models. Composition data even help us determine age. The universe was born almost exclusively in the form of hydrogen and helium. Other chemical elements, collectively called metals, formed in the stars, and at the end of the star’s life exploded again into space, where they are already involved in the formation of next-generation stars. Consequently, older stars have fewer metals, i.e. their metallicity is lower.
LAMOST data also contains metallurgy. Brightness and metallicity allow astronomers to determine the age of a star using computer models. Prior to Gaia’s mission, astronomers had to work tirelessly, and the uncertainty rate was at least 20-40 percent. As a result, the error in age figures was often equal to a billion years or more.
Gaia’s third collection of data changed all that. Gaia’s brightness data can be used to determine the age of subgiant stars with only a few percent probability of error. Scientists armed with accurate figures for the star ages of nearly a quarter of a million scattered across the galaxy have begun analyzes. The study was conducted by astronomers Mაშscheng Xiang and Hans-Walter Ricks of the Max Planck Institute for Astronomy in Germany.
Anatomy of the Milky Way
Our galaxy is made up of different components. In a broad sense, it can be divided into halo and disco. Halo is the spherical region around the disk and is traditionally considered to be the oldest component of the galaxy. The plate consists of two parts: a thin plate and a thick plate. The thin disk contains most of the stars that we see in the form of a white stripe in the night sky, called the Milky Way. The thick plate is almost twice as heavy as the thin one, but smaller in radius, containing only a few percent of the deer leap stars in the solar neighborhood.
However, by detecting subgiant stars in regions so different from each other, scientists were able to create a timeline of Milky Way formation, which came as a big surprise.
Two phases of Milky Way
The ages of the stars made it clear that the Milky Way went through two different phases of formation. In the first phase, which began 800 million years after the Big Bang, star formation began in a thick disk. At this point, the formation of the inner halo may have begun, but the end of that process accelerated rapidly about two billion years later when a dwarf galaxy called Gaia-Sausage-Enceladus collided with the Milky Way and merged. He filled it with halo stars, and as new research clearly shows, led to the birth of most of the stars in the newly formed thick disk. Then, in the second phase of the formation of the galaxy, a thin disk of stars formed, which included our sun, in the aftermath.
Analyzes also show that after the stellar birth wave caused by the Gaia-Sausage-Enceladus collision, star formation continued until gas was sufficient, about 6 billion years after the Big Bang. During this period, the metallicity of the disc increased approximately tenfold. But it is noteworthy that the researchers saw a very close stellar age – the connection of metallurgy, which indicates that during this period, the star-forming gas was well mixed with the entire disk. This in turn suggests that the disc deck regions of the early Milky Way must have originated from a highly turbulent gas that scattered metals far and wide.
Timeline from Gaia
The early age of the formation of the thick disk paints a different picture of the early history of our galaxy.
“Since we discovered the merger with the dwarf galaxy Gaia-Sausage-Enceladus in 2018, astronomers suspected that a Milky Way had already existed before the formation of Halo, but we did not have a clear picture of what our galaxy would look like then. The results of our research provide subtle details about this part of Deer Leap, such as its birthday, its stellar growth rate, and its history of metal enrichment. “These discoveries, thanks to Gaia, are revolutionizing our perception of when and how our galaxy formed,” Maosheng said.
And perhaps we have not yet seen such distant parts of the universe that we have seen similar details of the formation of a galactic disk anywhere. That is, it is difficult to detect the light that came before 13 billion light and has come down to us today.
We may be able to make such observations in the near future, when the optimization of the newly launched James Webb Space Telescope will be completed this summer, and we will see some of the earliest galaxies in the universe, such as Milky Way. Meanwhile, on June 13, 2022, the ship will send a new collection of Gaia data. This catalog will include spectrum and information on age and metallurgy, which will further simplify such studies.
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