[Epoch Times, January 11, 2022](The Epoch Times reporter Di Rui compiled and reported) An extremely ancient stellar belt has been discovered in the Milky Way, and the stars in it were born only about 3 billion years after the Big Bang. Even more peculiarly, they stayed together without being washed out, raising new questions about existing models of galaxy evolution.
A study published Jan. 5 in the journal Nature found a stream of stars called C-19 with stars 2,500 times less metallic than the Sun.
Metal abundance is the proportion of chemical elements heavier than hydrogen and helium. Astronomers believe that in the early days of the universe, there was only hydrogen, and various heavy elements were gradually produced in the process of continuous evolution. Astronomers use metal abundance as an important indicator to measure the age of celestial bodies – the lower the metal abundance, the more time it was born. The earlier you are, the older you are.
This star belt revolves around the center of the Milky Way outside the Milky Way, and its orbit is about 20,000 light-years closest to the center of the Milky Way and about 90,000 light-years farthest away.
The metallicity of star clusters in the Milky Way is generally close to 0.2%, while the metallicity of the C-19 stellar belt is less than 0.05%, which is the lowest level ever seen in the Milky Way and nearby the Milky Way.
Scientists believe that these ancient stars should have come from other galaxies or star clusters and appeared here after being merged into the Milky Way. “Most stars like the sun in our vicinity are Born in the Milky Way. However, there are a small number of stars and star clusters in the Milky Way, probably from other galaxies that are smaller than the Milky Way, which were incorporated by the Milky Way and stayed in the Milky Way.”
Existing models of galaxy evolution believe that many galaxies like the Milky Way continue to grow by merging with surrounding structures such as small galaxies and star clusters. If the merger is not too long ago, scientists can also detect features of the original structure of the celestial bodies before the merger from the existing structure. But over time, the interactions of these stars with other stars in the Milky Way can disrupt the structure of the stellar source population. Therefore, it is not easy for scientists to obtain information about galaxies and star clusters that have been incorporated into the Milky Way a long time ago.
But the C-19 stellar stream discovered this time is special. Based on its metallicity, the researchers speculate that these stars were born about 3 billion years after the Big Bang. Scientists believe that the Big Bang is nearly 13.8 billion years old. In other words, the universe gave birth to these stars when it was less than a quarter of its age. Hundreds of stars with such low metallicity have been found in the Milky Way, but never a structure in which all the stars in the entire group are so old.
Therefore, the discovery of C-19 surprised astronomers. It stands to reason that C-19 should also come from a very old star cluster that was merged into the Milky Way. From this point of view, the merger evolution model of the galaxy is correct, and it can also explain the hundreds of stars in the Milky Way mentioned above. The source of ancient stars – they should also come from other star clusters, the stars left after the original group structure was disrupted after the merger of the Milky Way. If this is the case, scientists speculate that the Milky Way has once merged with about five alien star clusters the age of C-19.
However, the discovery of C-19 raises a new question, why is this stream of stars not disrupted and the ancient stars inside can stay together forever? ◇
Responsible editor: Sun Yun#