Boring old fluorine had a stellar past. The cosmic origins of the chemical element have always been a mystery, as scientists have three competing theories for the source of fluorine on our planet. But astronomers now say that the very same ingredient found in many of our everyday products formed billions of years ago in long-dead stars that were a lot like our sun. The work was published in Astrophysical Journal Letters.
Fluorine was formed in now-dead stars that were the same type as the sun but heavier, and towards the end of their lives. Our sun and the planets in our solar system were also formed from the material from these dead stars, which is how our world came to be rich in the element. “So, the fluorine in our toothpaste originates from the sun’s dead ancestors,” says Nils Ryde of Lund University in a news release.
Ryde and an international team of astronomers studied stars formed at different points in the history of the universe to see if the amount of fluorine they contain supports one of the three theories over the others. They used telescopes in Hawaii and a new type of instrument sensitive to light with a wavelength in the middle of the infrared spectrum, and in high resolution -- a technology that just recently became available. By analyzing light emitted by a star, astronomers can calculate the amounts of various elements it contains. That’s because light at certain wavelengths corresponds to certain elements, which are formed at high pressure and temperature inside a star.
The team found that fluorine is formed towards the end of the star’s life, when it has already expanded to become a red giant; the element then moves to the outer parts of the star. Later the star casts off its outer parts, which go on to form a planetary nebula. Fluorine that’s thrown out in this process mixes with the interstellar medium -- the gas that surrounds the stars. This material will form new sun-like stars and planets, and when these new stars die, the cycle continues and the interstellar medium is enriched again.
