The mystery of heavy metals in oldest metal-poor stars

Context

Scientists from the Indian Institute of Astrophysics (IIA) have found a clue to the abundance of heavy metals in the oldest metal-poor stars that are born from the ejecta of first stars.

• The study was funded by the Department of Science & Technology.

About the Metal poor stars

• Metal-poor stars were formed from the ejected material of the first stars that formed after the Big Bang.
  • These stars show enhancement of carbon and are technically called Carbon Enhanced Metal-Poor (CEMP).
  • These stars carry the chemical imprints of early Galactic chemical evolution.
  • The study of these stars can help trace the origin and evolution of the elements in the Universe.
• The earlier studies showed that the heavy metals were formed due to the processes of nucleosynthesis-
  • It has two processes- slow and rapid neutron-capture processes. They are called s and r processes respectively.
    • The s-process elements were thought to be produced in low and intermediate-mass stars towards a final stage of stellar evolution.
    • The proposed sites of the r-process are exotic events such as supernovae and neutron star mergers.
• The CEMP stars with s-process and r-process elements are known as CEMP-s and CEMP-r stars respectively.
  • A subclass of CEMP stars, known as CEMP-r/s also exists.
  • This shows the enhancement of both s- and r-process elements.
• Key Finding: It is found that an intermediate process, the i-process is responsible for the peculiar abundance pattern of CEMP-r/s stars.
  • The i-process operates at neutron densities. It is an intermediate between those for s-process and r-process.
  • They have also put forward new stellar classification criteria based on the abundances of barium, lanthanum, and europium.