exit fromspecifically after from observable space contains from and D’ many of them and some lithium, but no trace of heavier elements such as , And . First which will form and eventually bring out from therefore, to a good approximation, we can assume that it does not contain and with zero as they say in their language, that is, devoid of elements heavier than helium.
According toit must first form small galaxies which will merge to give rise to large galaxies which will rapidly grow accreting guided by threads cold for the most part in accordance with the new paradigm of galaxy evolution, according to which these threads play a fundamental and only a secondary role in relation to all galaxies, contrary to what we thought more than a decade ago.
However, it is still believed thatinitially formed very similar to from rotating matter that gravitationally collapses. That counteracting this contraction perpendicular to the axis of rotation, the original cloud flattens out.
A galaxy whose chemical composition is changing
The theory of the structure and evolution of stars shows that stars evolve faster, the more massive they are. After 8solar panels, they will explode in after the fusion of heavy nuclei to , enriching the interstellar medium with galaxies in which new stars will be born. Therefore, there is a chemical evolution of stars and galaxies that allows them to be dated. In this way, poor in metallic elements other than lithium would point to a star born more than 10 billion years ago, while like our richer in heavy elements will be several billion years younger.
Thatstellar also predicts the size and a star will vary depending on its age for a given mass. Thus, some stars will see the fusion of nuclei of heavier elements in their cores stall while it continues in the shell around that core while the star is in a short phase called subgiant red, before finally becoming .
In short, by analyzing the chemical composition and brightness of a star, we can determine its age, and this is what astrophysicists have done with accuracy for about 250,000 stars invia Multiobject Fiber Optic Telescope Long Range Sky (i.e multi-object spectroscopy at Large field, abbreviated as Lamost) is a Chinese optical telescope with a diameter of four meters.
Maosheng Xiang and Hans-Walter Ricks of the Max Planck Institute for Astronomy in Heidelberg, Germany, together with their colleagues combined the Lamost data with data on the brightness and position of the same stars in the I’ set.Early Data Release 3 (EDR3) of the ESA Gaia astrometry satellite. The results of this combination have just been published in a renowned journal.
In this 2018 edition of Cosmos, we take to the stars as astronomers using Europe’s Gaia Space Telescope have compiled an unprecedented catalog of the Milky Way’s billion stars, paving the way for decades of discovery. © euronews
Galactic archeology read in layers of stars
Gaia astrometric data refers to precise measurements of the position and velocity of approximately 1.5 billion stars in the Milky Way. The latter were published in December 2020 and Lamost provided information on 9 million stars in 2021. Only a few of these stars were in the red subgiant phase, 250,000 were studied with the help of Lamost, but, in the end, the structure and dating of the halo and disk of the Milky Way were refined.
Its structure is twofold. First comes a thin, dense disk, the thickness of which is about 2000where is our weapon where most stars are born today. He himself is immersed in the disk more the thickness of which is about 6000 light years.
The thin disk contains most of the stars that we see as a hazy streak of light across the sky.what we call the Milky Way. The thick disk is more than three times the height of the thin disk, but is smaller in radius and contains only a few percent of the Milky Way’s stars in the vicinity of the Sun.
initself consists of a nearly spherical population of stars and surrounding the Milky Way. The stars there are old with low metallicity, as in the case of the central bulge of the Milky Way. There is no dust there, unlike the disk. This halo itself is immersed in a hot plasma halo, which in turn must be shrouded according to the standard cosmological model.
Another galactic timeline
Now it seems, and this is a surprise, according to the ESA statement, that there would be two distinct important stages in the history of the Milky Way.
At the first stage, which began just 0.8 billion years afterand so about 13 billion years ago the thick disk is already there, contrary to what we thought, and it starts to form stars there. But about 2 billion years later, after the rate of star formation accelerates, there is a big peak, which is explained by the merger of the young Milky Way and , a galaxy called Gaia-Enceladus. This name comes from Greek mythology: one of the Giants, the son of Gaia (Earth) and Uranus (Heaven), during the Gigantomachy was disabled by Athena and buried under the mountain calling ever since and eruptions.
This merger was, of course, comparable to the mass thrown and hitting the pool in the self-gravitating stellar fluid of our Galaxy, and it was believed that it was he who somehow “heated” the stellar gas of the thin disk. , causing it to evaporate and expand, forming a thick disk.
It was at this time that the stellar halo should have formed at the same time and for the same reason.
But in the scenario now proposed, only after this merger would a thin disk be born, and star formation in the thick disk would continue until its gas content was depleted about 6 billion years after the Big Bang. During this time, the metallicity of a thick disk would increase by more than 10 times.
As a bonus, the astrophysicists determined that the metallicity in this disk was relatively uniform, meaning that turbulent mixing processes ensure efficient transport and mixing of newly formed elements ejected into the interstellar medium during supernova explosions.
This scenario is probably typical for many large spiral galaxies. Perhaps we will learn about this from observations that will be made in the next decade..