Until today, he was suspected but never found. Our galaxy, the Milky Way, has a core of stars, among the first ever to host it. And researchers have just proven its existence, thanks to the latest data collected by the Gaia satellite!
From its highest diameter of 100,000 light-years, our galaxy is Milky WayIt is home to between 100 and 400 billion stars. They belong to barred spiral galaxies, yet they contain a halo of stars all over the galactic disk. The density of stars is less there, but it is still there. Like most disk galaxies, it was formed primarily by collisions with other smaller galaxies. Then it absorbed them little by little, until the two stars became one! But researchers have studied another part of the origin of our galaxy: what they call Galaxy Core Stars near the center that date back to the Milky Way’s earliest moments, less than a billion years after the Big Bang. The results of their study were previously published on the server arXiv.
Two scenarios for the formation of the Milky Way
Composed of astronomers and astrophysicists, the team practices what is called galactic archeology: researchers try to understand history, formation of galaxiesBe it us or those around him. However, according to the study, two scenarios could lead to a galaxy with a disk as massive as ours. The two scenarios often overlap. First, the researchers demonstrated that a primordial core consists of metal-poor stars. This is because in the early universe, only the lightest elements were present, hydrogen and helium. Then more dense clouds were formed, called protogalaxies, and from them the first stars were born, and then galaxies! Elements heavier than helium, which are referred to as “metals” in astrophysics, are distributed only in interstellar interstellar Only after the first supernova, massive star explosions at the end of their lives. Therefore, according to the study, “Huge disk galaxies such as our Milky Way should host an ancient, centrally located, mineral-poor star cluster.”
After this first core is created, intergalactic mergers arrive, which can also replace the formation ofprimordial stars : “In the context of the hierarchical formation of massive disk galaxies such as the Milky Way, we would expect that older, metal-poor stars may have formed within one of the major excess densities that merged early to form the protogalactic, or formed early into separate satellite galaxies that eventually merged with the body The main. The first channel is usually referred to as in situ formation, and the second is accumulating.” The researchers’ goal was specifically to distinguish between these two scenarios!
According to them, it all started with a core On siteSo the formation of stars inside a cloud of hydrogen and helium, and then various collisions caused the galaxy to swell. Researchers in particular evoke a collision with the galaxy Gaia Enceladus 11.5 billion years ago and several consecutive collisions with the dwarf satellite galaxy Sagittarius, still orbiting the Milky Way. In addition to these two known events, the study points to other evidence of an enlarged galaxy: “An increasing number of accumulating distinct plug-ins have been identified for the galaxy.”
18,000 stars with extremely low mineral content have been found
To find this mysterious essence On siteThe researchers went on to track about two million giant stars, located less than 30 degrees from the galactic center, in the direction of Sagittarius. They then proceeded to calculate their mineral, based on the relative amount of iron in these stars compared to hydrogen, and compare it to the Sun. For this purpose, they used the latest data collected by the Gaia satellite, which was unveiled on July 12, 2022. They found a group of 18,000 stars, both ancient, dating back nearly 12.5 billion years. Years, double the metal! All this for a mass of 5.107 Solar masses, but calculated at 108 Solar masses take into account dust dimming of about 0.2% of the galaxy’s total mass.
So far, ancient stars with low metallic content have been found, such as SDSS J102915 + 172927 About 13 billion years ago, or HE 1523-0901, the oldest in the galaxy, is located in the galactic halo. But they are all isolated: this is the first time such an ancient pool has been found! The study also shows that stars are found ” showing no net rotation”, Unlike stars with higher metallics, which are ” controlled by rotation”. A result that testifies more to the age of these stars, they were formed when the galaxy was not one yet, and it had not yet begun its rotation!
Thus, for researchers, “All of this information fits into an image in which this mineral-poor core of the Milky Way is the oldest elemental component of our galaxy.” They conclude by explaining that their findings It is by no means a new stellar component distinct from the Milky Way,” And the “The spatial distribution of this population deserves quantitative modeling”. Further studies will reveal this nucleus. On site subordinate Milky WayAnd so in his past!
