A new discovery has shed light on how fluorine, an element found in bones and teeth like fluoride, is formed in the universe.
Using the European Southern Observatory’s (ESO) Atacama Large Millimeter/submillimeter Array, known as ‘ALMA’, a team of astronomers has detected this element in a galaxy so far away, that its light took more than 12 billion years to reach us.
This is the first time that fluorine has been observed in such a distant star-forming galaxy.
“We all know about fluorine because the toothpaste we use daily contains it in the form of fluoride,” says Maximilian Franco of the University of Hartfordshire in the United Kingdom, who led the new study, published in Nature Astronomy. “But until now, we didn’t know exactly how this element was produced. We didn’t even know which type of star produced the majority of the fluorine in the universe.”
Franco and his colleagues discovered fluorine (in the form of hydrogen fluoride) in large clouds of gas in the distant galaxy NGP-190387, which we see when the universe was only 1.4 billion years old, about 10% of its current age.
Since stars expel the elements they form in their cores when they reach the end of their lives, this discovery means that the stars that created fluorine must have lived and died quickly.
The team believes that Wolf-Rayet stars, very massive stars that live only a few million years, are probably the most likely places to produce fluorine.
They say the Wolf-Rayet stars are necessary to explain the amounts of hydrogen fluoride the team detected.
It is noteworthy that Wolf-Rayet stars have been suggested as possible sources of cosmic fluorine before, but astronomers do not yet know how important it was in the production of this element in the early universe.
“We’ve shown that Wolf-Wright stars, which are among the most massive known and can explode violently towards the end of their lives, in some way help us maintain good dental health,” Franco said.
In addition to these stars, scientists have proposed other scenarios for how fluorine was produced and expelled in the past. An example is the pulses of advanced giant stars with masses up to several times the mass of our Sun, called asymptotic giant subsidiary stars (a stage of stellar evolution that results from the evolution of small and medium-sized stars).
But the team believes that these scenarios, some of which take billions of years to occur, may not fully explain the amount of fluorine in NGP-190387.
“For this galaxy, it took tens or hundreds of millions of years to get fluorine levels similar to those found in stars in the Milky Way, which is 13.5 billion years old,” says Chiaki Kobayashi, a professor at the University of Hartfordshire and co-author of the study. This was a completely unexpected result… Our measurement adds an entirely new limitation to the origin of fluorine, which has been studied for two decades.”
The discovery at NGP-190387 represents one of the first discoveries of fluorine outside the Milky Way and its neighboring galaxies.
Astronomers have previously discovered this element in distant quasars, which are bright objects powered by supermassive black holes at the center of some galaxies. But this element has never been observed in a star-forming galaxy so early in the history of the universe.
The team’s discovery of fluorine was a possible discovery opportunity thanks to the use of space and ground-based observatories. Scientists found the galaxy NGP-190387 originally, thanks to the Herschel space observatory of the European Space Agency, and later with the “ALMA” observatory based in Chile, which is an exceptionally bright galaxy in view of its distance.
ALMA data confirmed that the extraordinary brightness of NGP-190387 was caused in part by another massive galaxy known, located between NGP-190387 and Earth.
This massive galaxy amplified the light observed by Franco and his collaborators, enabling them to determine the faint radiation emitted by billions of years of fluorine at NGP-190387.
Future studies of NGP-190387 with the Extremely Large Telescope (ELT), under construction in Chile and due to begin operations later this decade, may reveal more secrets about this galaxy.
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