Bright ancient star G256353 shows strong r-process element enrichment

Star system: HD 222925 | Distance from the Sun: 1469 light years

Astronomers have studied four extremely metal-poor stars, which are among the oldest and most primitive in our galaxy. The main focus is on G256353, a star with a very low iron content and a strong enhancement of elements created by the rapid neutron-capture process, known as the r-process. Using high-resolution spectra from the GHOST instrument on Gemini South, the team measured the abundances of 15 neutron-capture elements in G256353. The pattern of these elements closely matches that seen in the Sun and in another r-process-rich star, HD 222925, as well as predictions from neutron star merger models.

The study also compared the light-element abundances of all four stars to models of the first generation of supernovae, suggesting that their progenitors were massive stars about 20 to 30 times the mass of the Sun. One of the stars, Gaia DR3 2887334237669844480, appears to have been accreted from another galaxy, based on its motion and chemical makeup. Its low strontium and barium content supports this origin. The findings reinforce the idea that the main r-process operates similarly in different environments, from the early universe to neutron star mergers.

These results help astronomers understand the origins of heavy elements and the history of the Milky Way, showing that ancient stars can preserve the chemical fingerprints of the earliest cosmic events.

Key findings
- G256353 is a bright, extremely metal-poor star with strong r-process element enrichment.
- The heavy-element pattern matches the Sun, HD 222925, and neutron star merger models.
- Light-element abundances suggest massive Population III supernova progenitors.
- One star in the sample likely originated from an accreted structure in the Galactic disk.
- The study supports the universality of the main r-process across cosmic environments.

Scientific study

The R-process Alliance: A Bright, Strongly R-process-enhanced Extremely Metal-poor Star Observed with GHOST (external link)