Unlocking the Secrets of Ancient Galaxies

Elliptical galaxies hold a fascinating secret in their ultraviolet (UV) light. This secret could help scientists figure out how old these galaxies are. Recent studies have shown that the UV light from these galaxies comes from different types of stars. Some are metal-poor, and others are metal-rich hot horizontal-branch (HB) stars. However, when looking at galaxies that are very far away, the UV light is mostly from post-asymptotic-giant-branch (PAGB) stars. This is important because the mass of these PAGB stars is not well known. This makes it hard to understand the UV light from these ancient galaxies. But there's good news! Scientists think that by studying the far-UV light from galaxies that are more than 3. 5 billion light-years away, they can learn more about the mass of PAGB stars. For galaxies that are closer, but still very far, scientists can still learn about the origin of the UV light. Future space missions, like those using the Hubble Space Telescope and the GALEX facility, will give scientists more data. This data will help them better understand how to use UV light to figure out the age of these ancient galaxies.