The study, published in the journal Astronomy & Astrophysics, analyzed age data from more than 100,000 giant stars obtained from comprehensive sky surveys such as APOGEE, LAMOST and Gaia. The data showed an interesting “U-curve” shaped relationship between the stellar age in the galaxy and the distance from the center.
The secret of the “U” curve in the sidereal age
The high density of gas and dust in the regions near the center of the galaxy means that star formation begins very early and therefore old stars are present there.
As gas density decreases with increasing distance from the center, star formation slows and stars gradually become younger. However, when a distance of 40,000 light years was reached, a “break point” was detected where the stars began to age again.
“Immigrant” stars across the border
It was found that ancient stars outside the star-forming region were actually “immigrant stars” that formed inside the galaxy and were displaced over time.
These stars are estimated to be thrown outward by the gravitational forces of the bar structure, or spiral arms, at the center of the galaxy.
This discovery identifies the Milky Way as a “Type II (Down-Twist) Disk Galaxy,” which belongs to the same group as 60 percent of similar galaxies in the Universe.
By clarifying where the Milky Way's productive youth ends and its quieter outskirts begin, this study is of great importance for understanding the evolutionary history of our galaxy.
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