White dwarfs, the compact remnants of low- and intermediate-mass stars, offer potential insights into solving the cosmological lithium problem—the observed discrepancy between the lithium abundance predicted by the standard Big Bang nucleosynthesis (BBN) model and the abundance measured in metal-poor stars. Here's how white dwarfs can contribute to addressing this problem:

Lithium Destruction: White dwarfs can destroy lithium through various processes occurring in their interiors. As white dwarfs cool and their outer layers become degenerate, they develop a region known as the convective envelope. Within this envelope, lithium can be efficiently burned into helium via reactions involving protons or other light nuclei. This lithium destruction helps to reduce the primordial lithium abundance predicted by BBN.

Accretion from the Interstellar Medium: White dwarfs can accrete matter from the surrounding interstellar medium, including gas and dust containing lithium. This process can introduce additional lithium into white dwarf atmospheres, potentially increasing the observed lithium abundance. By studying the accretion rates and the chemical composition of the accreted material, astronomers can gain insights into the lithium enrichment processes and constrain the overall lithium budget in the Galaxy.

Stellar Mergers and Mass Transfer: In binary star systems containing a white dwarf and a companion star, mass transfer can occur between the components. If the companion star is relatively lithium-rich, it can transfer lithium to the white dwarf during specific evolutionary stages. This scenario allows for the enhancement of lithium in some white dwarfs.

Lithium Retention: Some white dwarfs may preserve their original lithium abundance if they avoid efficient lithium destruction mechanisms. This can occur in certain evolutionary scenarios, such as those involving stable mass transfer or a particular range of stellar masses. By identifying and studying such white dwarfs, astronomers can obtain valuable information about the initial lithium content and the conditions under which lithium is retained.

By exploring the lithium abundances in white dwarfs and understanding the processes that affect lithium destruction and enrichment, astronomers can provide important constraints on the BBN model and help refine our understanding of the early Universe. However, it's crucial to consider the limitations and biases associated with white dwarf observations and to combine insights from multiple sources to fully address the complexities of the cosmological lithium problem.