In the first billion years of the universe’s existence, many stars were born, but not all of them are still shining. Many of these early stars have already faded, exploding into supernovae or becoming other objects. However, some of them still exist and researchers report finding them around the Milky Way’s core. Moreover, they have revealed interesting information about how these stars move.
To find the oldest stars in our galaxy, astronomers look for those that do not contain “contamination.” The earliest stars consisted only of hydrogen and helium, and all the other elements, which are called metals, were formed in these stars. Therefore, a star with low metallicity, containing only small amounts of elements heavier than helium, is a star that formed a very long time ago. Such stars are easier to find away from the plane of the Milky Way.
However, a team of astronomers decided to look for these stars in the galaxy’s most populous region – its center, known as the bulge. This was a challenge because this region is dominated by young stars. Dr. Anke Arntsen of Cambridge University worked to create a real sample of these ancient stars.
The study focused on the motion of these stars around the balge, the central region of the Milky Way. It turned out that they move in peculiar orbits, forming a chaotic group, but still maintaining an average rotation that coincides with the rotation of the Milky Way disk. Their orbits and interactions also never took them too far from their birthplace. They spent most of their lives in the inner Milky Way, never moving further than 10,000 light-years from the center. While the Sun is 26,000 light-years away.
This discovery allows scientists to better understand the origin and evolution of stars in the galaxy. It confirms the assumption that the bulge formed first and contains older stars. Researchers believe that these stars remain in the center of the Milky Way without moving significant distances.
This work was presented at the National Astronomy Meeting 2023 at Cardiff University. It provides new data and insight into the movement and location of ancient stars in the Milky Way.