Astronomers have made the most distant detection yet of fluorine in a star-forming galaxy.
The new discovery is shedding light on how the element – found in human bones and teeth as fluoride – is forged in the universe.
Researchers detected the element in a galaxy that is so far away its light has taken more than 12 billion years to reach Earth.
It is the first time fluorine has been spotted in such a distant star-forming galaxy, they say.
The team used the Atacama Large Millimetre/submillimetre Array (ALMA), in which the European Southern Observatory (ESO) is a partner, to make the discovery.
Maximilien Franco, from the University of Hertfordshire, who led the new study, said: “We all know about fluorine because the toothpaste we use every day contains it in the form of fluoride.”
Like most elements, fluorine is created inside stars but, until now, scientists did not know exactly how it was produced.
“We did not even know which type of stars produced the majority of fluorine in the universe,” Mr Franco said.
The researchers spotted fluorine, in the form of hydrogen fluoride, in the large clouds of gas of the distant galaxy NGP–190387.
The galaxy is seen as it was when the universe was only 1.4 billion years old – about 10% of its current age.
Researchers say that since stars expel the elements they form in their cores as they reach the end of their lives, the detection implies the stars that created fluorine must have lived and died quickly.
The team believes very massive stars called Wolf-Rayet stars, that only live a few million years, are the most likely production sites of fluorine.
They are needed to explain the amounts of hydrogen fluoride the team spotted, they say.
While Wolf–Rayet stars had been suggested as possible sources of cosmic fluorine before, astronomers did not know until now how important they were in producing this element in the early universe.
Chiaki Kobayashi, a professor at the University of Hertfordshire, said: “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.”
Other explanations for how fluorine is produced and expelled have been put forward in the past.
One example includes pulsations of giant, evolved stars with masses up to few times that of our Sun, called asymptotic giant branch stars.
But researchers believe these scenarios might not fully explain the amount of fluorine in the galaxy they observed.
The team says the discovery of NGP–190387 marks one of the first detections of fluorine beyond the Milky Way and its neighbouring galaxies.
In the past astronomers had spotted this element in distant quasars – bright objects powered by supermassive black holes at the centre of some galaxies.
This is the first time it has been observed in a star-forming galaxy so early in the history of the universe.
