Discovery of Ancient Star Sheds Light on Early Universe's Chemical Evolution

Astronomers have discovered PicII-503, a second-generation star located in the ultra-faint dwarf galaxy Pictor II, approximately 150,000 light-years from Earth. This star exhibits the lowest iron abundance ever detected outside the Milky Way, containing only 1/40,000th the iron found in the Sun. Additionally, PicII-503 displays a carbon-to-iron ratio over 1,500 times greater than that of the Sun, a pattern known as carbon-enhanced metal-poor (CEMP) stars.

The chemical composition of PicII-503 suggests it formed from material enriched by the first generation of stars, known as Population III stars. These early stars, composed primarily of hydrogen and helium, ended their lives in low-energy supernovae that expelled lighter elements like carbon into the surrounding gas, while heavier elements such as iron fell back into the remnants.

Pictor II, the host galaxy of PicII-503, is a small system with several thousand stars, located near the Large Magellanic Cloud. Its stars are over ten billion years old, providing a lasting record of early cosmic history.

The discovery of PicII-503 was made using the Dark Energy Camera (DECam) on the Víctor M. Blanco 4-meter Telescope in Chile. The star was identified through the MAGIC survey, which aims to find the oldest and most chemically primitive stars in the Milky Way and its satellite galaxies.

This finding offers a rare glimpse into the chemical evolution of the early universe and supports the hypothesis that CEMP stars originate from low-energy supernovae in small, early galaxies.