Cavity-fighting stardust? Fluorine found in galaxy 12 billion light years from Earth

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HATFIELD, England — A galaxy twelve billion light-years from Earth is found to contain fluorine, the natural mineral used in toothpaste to strengthen enamel and prevent cavities. The dusty, star-forming galaxy called NGP-190387 indicates the origin of fluorine from burned-out stars – some as old as 1.4 billion years old. The discovery means we brush our teeth with the remains of suns similar to our own.

“We all know about fluorine because the toothpaste we use every day contains it in the form of fluoride,” says study lead author Dr. Maximilien Franco of the University of Hertfordshire in England, in a statement.

Like most elements, flourine created inside stars, but scientists never knew how — until now. “We did not even know which type of stars produced the majority of fluorine in the universe,” adds Franco.

The international team used the ALMA radio telescope high in the Andes mountains of Chile to make the most distant discovery of its kind. Large clouds of gas in the far away galaxy show the stars that created fluorine lived and died quickly. Elements that form in their cores are expelled as they reach the end of their lives.

Massive “Wolf-Rayet” stars that live only a few million years — a blink of an eye in cosmic terms — are the most likely production factories. They explain the amounts of hydrogen fluoride identified from an analysis of light wavelengths. “We have shown Wolf-Rayet stars, which are among the most massive stars known and can explode violently as they reach the end of their lives, help us, in a way, to maintain good dental health,” Franco quips.

Other theories for how fluorine is produced and expelled have been put forward in the past. They include pulsations of giant, evolved stars with masses up to a few times that of our Sun, called asymptotic giant branch stars. But the team believes these scenarios, some of which take billions of years to occur, don’t explain the amount of fluorine in galaxy NGP-190387.

“For this galaxy, it took just tens or hundreds of millions of years to have fluorine levels comparable to those found in stars in the Milky Way, which is 13.5 billion years old. This was a totally unexpected result. Our measurement adds a completely new constraint on the origin of fluorine, which has been studied for two decades,” notes co-author Chiaki Kobayashi,  also a professor at Hertfordshire.

The discovery in NGP–190387 marks one of the first detections of fluorine beyond the Milky Way and its neighboring galaxies. Astronomers have previously spotted the element in distant quasars — astonishingly bright objects powered by supermassive black holes. But never before had it been observed in a star-forming galaxy so early in the history of the universe.

The serendipitous discovery was made possible thanks to the use of space and ground-based observatories. NGP–190387, originally discovered with the European Space Agency’s Herschel Space Observatory, is extraordinarily bright for its distance.

The ALMA data confirms the exceptional luminosity was partly caused by another massive galaxy located between NGP-190387 and the Earth. It amplified the light observed by Dr. Franco and colleagues, enabling them to spot the faint radiation emitted billions of years ago by the fluorine in NGP-190387. Future studies with the flagship Extremely Large Telescope (ELT) under construction in Chile and set to start operations later this decade could reveal further secrets.

The discovery is published in the journal Nature Astronomy.

South West News Service writer Mark Waghorn contributed to this report.