Discovered ancient star-New data show that some of the ancient stars in the Milky Way were not locate in areas that astronomer thought they should be. Scientists use the metal content of stars to infer about age. They believe that in the early days of the universe, there were only the lightest elements such as hydrogen and helium. Over the course of subsequent fusion and other evolutions, heavier element continue to be synthesize. Therefore, stars with low metal content are consider old.
Discovered ancient star-Astronomers divide stars into groups based on the ratio of hydrogen to helium [Fe/He], and use our sun as the base point. Group I stars are stars whose; ratio is at least 10% or more of that of the sun. Group II has a lower proportion and is more ancient. Group III is the oldest type of star. It is also consider to be the first stars after the birth of the universe. It contains no metal elements.
From the perspective of our Milky Way galaxy; astronomers have discovered that; the youngest group I stars are distributed; in the flat “silver disk” of the Milky Way, especially in the spiral arms of the Milky Way. Older stars are located in areas above or below the plane of the Milky Way; such as the bulging part in the middle of the Milky Way. The stars scattered in the far area beyond the plane; of the silver disk are the stars with very low metal content and are older stars in the II group.
For a long time, scientists have also believed; that this distribution can be explained by known theories; the galaxy’s silver disk is a dense area of gas and dust;especially in the spiral arm region, where stars are born from these materials. Over time under the influence of gravity; these stars began to move away from the plane of the Milky Way and move to the periphery. Older stars are farther away from the Milky Way disk.
However, recent observations from the SkyMapper research group in Australia have found inconsistent features.
They observed 475 ancient stars with a [Fe/He] ratio of less than one thousandth of the sun . According to speculation, these ancient stars should be located far from the outer area of the silver disk. However, 11% of the orbital planes of these stars lie within the plane of the galactic disk.
And their orbits are very close to the circumference, similar to the orbit of our sun. This is surprising and cannot be explained by existing galaxy evolution models.
The researchers said that with the progress; of large-scale observation projects, people’s understanding of the evolution of the Milky Way will continue to be expanded. Even the initial data of this research has clearly demonstrated the limitations of existing cognition.
This research was recently publish in Monthly Notices of the Royal Astronomical Society.