Shining light on the timescale of the Sun’s formation

Team successfully measure the bound-state beta decay of fully-ionized thallium-205 ions.

How long did it take for our Sun to form within its stellar nursery? An international team of scientists has come closer to finding out.

Radioactive nuclei with lifetimes on the order of millions of years can reveal the formation history of the Sun and active nucleosynthesis occurring at the time and place of its birth. Among such nuclei whose decay signatures are found in the oldest meteorites, lead-205 is a powerful example. However, making accurate abundance predictions for lead-205 has so far been impossible because the weak decay rates are very uncertain at stellar temperatures.

To constrain these decay rates, a team of scientists measured the bound-state beta decay of fully ionized thallium-205 ions, an exotic decay mode that only occurs in highly charged ions. Work took place at the Experimental Storage Ring at the GSI/FAIR facility in Germany.

With new, experimentally backed decay rates, they used stellar models to calculate lead-205 yields. They found positive isolation times that are consistent with the other short-lived radioactive nuclei found in the early Solar System.

The results reaffirm the site of the Sun’s birth as a long-lived, giant molecular cloud and support the use of the lead-205–thallium-205 decay system as a chronometer in the early Solar System.

Dr Ragandeep Singh Sidhu, the study’s second author, who is based in the School’s Nuclear Physics research group said:

This significant result enhances our understanding of how radioactive lead-205 is produced in asymptotic giant branch stars and sheds light on the timescale of the Sun’s formation.

The results have been published in Nature.