A brief history of the New Galactic Empire: Born 13 billion years ago, it was repeatedly invaded by foreign races-

The center of the Milky Way in infrared wavelengths taken by the Spitzer Space Telescope. NASA / JPL-Caltech

Researchers from the Max Planck Institute for Astronomy in Heidelberg, Germany, recently analyzed nearly 250,000 subgiants and conducted a more detailed analysis of the evolution of our galaxy than before. Clear combing. They found that the Milky Way appeared shortly after the birth of the universe. At that time, the Milky Way had a much thicker galactic disk than now, and the halo was formed after the Milky Way was invaded later.

A subgiant is a type of star that has burned out the hydrogen fuel in its core and has begun to expand and cool. By analyzing the surface temperature and luminosity of such stars, their age can be determined, allowing researchers to understand the evolution characteristics of stars in various parts of the Milky Way.

Researchers have found that the Milky Way's galactic disk took shape about 13 billion years ago. At that time, the universe was only about 800 million years old. But the galactic disk was very thick at that time: where our solar system is today, it was about 6,000 light-years thick. And between 13 billion and 8 billion years ago, this place had always been an active star-producing area.

Researchers have found a very tight correlation between the ages of primordial disk stars and their iron content.

The successive supernova explosions caused the iron content of the original galactic disk to increase by 30 times during this period. The iron content of newborn stars increased from only one-tenth of the sun at the beginning to three times that of the sun after 5 billion years. As the gas cloud spreads, the iron content in all corners of the galactic disk gradually levels out, so that all newborn stars end up with almost the same amount of iron - compared with initially only stars closer to the center of the Milky Way.

The Milky Way is not an empire with a single ethnic group. About 11 billion years ago, the Milky Way first collided with other galaxies - and the alien invasion began.

After entering the Milky Way, intergalactic immigrants mainly stay in the outer reaches of the Milky Way. They wrap around the main part of the Milky Way, forming a huge and sparse halo. When a large amount of alien galaxy gas collided with the native gas of the Milky Way, it triggered a large-scale star-making movement, pushing the star production rate of the Milky Way to a "historical" high 11 billion years ago.

The merger also caused some of the Milky Way's native stars to enter the galactic halo. They are significantly different from the immigrant stars that make up the main component of the galactic halo because they contain more iron.

The gas in the original galactic disk was exhausted about 8 billion years ago, and no new stars were produced; and the remaining galactic gas gradually gathered into a thinner disk-like structure. This new modern galactic disk is only about 2,000 light-years thick, but it gave birth to many new generations of stars, including our sun.

In the next 8 billion years, no larger galaxies have collided with the Milky Way, and this island universe has been in a relatively calm and peaceful state.

But things are unpredictable: the Milky Way is approaching a behemoth, the Andromeda Galaxy. If the two merge in the future, the appearance and structure of the Milky Way will be completely changed.