Stars around the Milky Way: captives or exiles?

Stars around the Milky Way: captives or exiles?

The Milky Way galaxy perturbed by tidal interaction with a dwarf galaxy. The locations of the observed stars above and below the disk used to test the perturbation scenario are indicated.

The researchers examined a small stellar population in the halo of the Milky Way and found that the chemical composition corresponds to the data of the galactic disk. This is convincing evidence that the stars appeared inside the disk, and not in the united dwarf galaxies. It is believed that the cause of stellar migration is the theoretical oscillations of the galactic disk created by the tidal contact of our galaxy and the massive neighbor passing.

If someone wanted to send us a letter, the space address would include several chains: Earth, Solar System, Orion Spiral Sleeve, and the Milky Way. We understand the structure, but our position does not allow to cover everything with a global view. It also interferes with time. How to interpret galactic evolution if our own lifespan is negligible?

Now we have a picture of what is happening in the Milky Way and other galaxies. Scientists attribute our home to a large spiral type with a large number of its stars in the central disk and dusty stars that go beyond the galactic halo. It seems that halo stars are not randomly distributed. Many of them are grouped into giant structures — huge streams and clouds surrounding our galaxy. They are used to be called peculiar traces of a turbulent galactic past — fragments of small galaxies that were previously absorbed.

Scientists have studied the characteristics of stars to learn more about the past of the Milky Way. Locations and the movement of objects provide the key to understanding the capture scenario, and the chemical composition will tell a lot about the predecessor galaxy. However, in a recent study, scientists prove that some of the structures of the halo come from the galactic disk!

The researchers undertook the analysis of 14 stars in two different structures of the galactic disk: the Triangle Galaxy and the A13 stellar superplanes. Early studies have shown that they are kinematically connected and can communicate with the Ring of the Unicorn - a ring-shaped structure around the Milky Way. Each plane is located 14,000 light years above and below the galactic plane.

The Keck Observatory and the Very Large Telescope for the first time made it possible to obtain a detailed chemical composition of such stars. Comparing the results with indicators of other chemical structures, the researchers noted with surprise that they are almost the same and resemble the stars in the Milky Way disk. So, they were formed in a thin galactic disk, and are not garbage of the former galaxies. But how did they get so far? In theory, this is possible if the stars move to large vertical distances from the place of birth to the plane of the disk. This migration can be explained by disk oscillations.

New findings are important because they show that the galactic disk and its dynamics are much more complicated than originally thought. In the future, scientists plan to analyze the spectra of other stars in the same superplanes and other star structures that live farther from the disk.

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