Measurement parameters and uncertainties of the three stars considered (orange star 31, red star 36, blue star 39). The color-filled region contains isochron points in the range of age and metallicity of each star. The dotted line corresponds to the isochron with the reporting age. **Astrophysical Journal Letters (2023). doi： 10.3847/2041-8213/ad08b1
By analyzing high-resolution data from the 10-meter telescope in Hawaii, researchers at Lund University in Sweden have succeeded in generating new knowledge about the three stars at the center of the Milky Way. The stars proved to be unusually young, and their chemistry was puzzling, much to the surprise of researchers.
The study, which has been published in the Astrophysical Journal Letters, examines a group of stars located in the nuclear cluster that makes up the center of the Milky Way. It involves three stars that are difficult to study because they are very far away from our solar system and are hidden behind huge clouds of dust and gas that block light. In fact, the region is also full of stars, which makes it very complicated to distinguish individual stars.
In a previous study, the researchers proposed a hypothesis that these particular stars in the middle of the Milky Way galaxy could be unusually young.
We can now confirm this. In our research, we have been able to determine that three of these stars are relatively young, at least in the case of astronomers, around 100 million to 1 billion years old. This can be compared to the sun, which is 4.6 billion years old," said Rebecca Forsberg, an astronomy researcher at Lund University.
Nuclear clusters are mostly seen as very old parts of the Milky Way, and rightly so. But the researchers' new discoveries about these young stars suggest that active stars are also forming in this ancient component of the Milky Way. However, stellar dating with a 25,000 light-year distance from Earth is not something that can be done in a hurry.
Researchers used high-resolution data from the Keck 2 telescope in Hawaii, one of the largest telescopes in the world, with a mirror diameter of 10 meters. To further verify, they then measured how much heavy element iron was present in the star. This element is important for tracking the development of galaxies because astronomers' theories about how stars form and how galaxies develop suggest that younger stars have more heavy elements because heavy elements form more and more in the universe over time.
To determine the amount of iron, astronomers looked at the spectrum of stars in infrared light, which is part of the spectrum that makes it easier to pass through the dense parts of the Milky Way than optics. The results surprised the researchers by showing that iron levels varied widely.
The wide distribution of iron levels may indicate that the innermost layer of the Milky Way is incredibly inhomogeneous, i.e., unmixed. This is something we didn't expect, illustrating not only how the center of the galaxy appeared, but what the early universe looked like," said Brian Thorsbro, an astronomy researcher at Lund University.
This study provides important insights into our understanding of the early universe and the functioning of the center of the Milky Way. The findings may also help stimulate continued and future exploration of the center of the Milky Way, as well as further develop models and simulations of galaxy and star formation.
Personally, I think it's very exciting that we can now study the center of the Milky Way at such a high level of detail. These types of measurements have always been the standard for observing the disk of the galaxy in which we are located, but for the more distant and exotic parts of the Milky Way, it is an unattainable goal. We can learn a lot from these studies about how our home galaxy formed and developed," concluded Rebecca Forsberg.
More information: bThorsbro et al., Wide metallicity range of GYR-OLD stars in nuclear clusters, Astrophysical Journal Letters (2023). doi： 10.3847/2041-8213/ad08b1