(CN) — For the first time, fluorine — the chemical element found as fluoride in bones, teeth and toothpaste — has been discovered outside the Milky Way in a galaxy so far away it’s taken over 12 billion years for its light to reach Earth.
How fluorine is created has been a point of debate, but like most elements that make up the planets — and even our bodies — it’s known to have first formed inside stars, according to the Herschel Space Observatory’s history of chemicals.
The process begins when a star forms from a hydrogen cloud. The star’s core generates heat that ignites a reaction, known as nucleosynthesis, that converts the hydrogen into helium. The more mass a star has, the more rounds of nucleosynthesis it can have, each time producing heavier elements until it produces an iron core.
Once a star forms an iron core, its days are numbered, the space observatory notes. That’s because instead of producing energy, which creates an outward pressure that counterbalances the inward pressure of gravity, iron fusion uses up energy. That inward pressure then takes over until the star implodes. A variety of new elements are released into the gas that surrounds the stars, and they themselves may become new stars and restart the process.
Fluorine is created during that process.
The element was first measured in stars apart from the sun in 1992.
“We all know about fluorine because the toothpaste we use every day contains it in the form of fluoride,” Maximilien Franco, of the University of Hertfordshire in the United Kingdom, said in a statement.
But while it’s known fluorine is produced in stars, “We did not even know which type of stars produced the majority of fluorine in the universe,” Franco added.
Franco, who led a team of astronomers in Chile, spotted fluorine in the form of hydrogen fluoride in the large clouds of gas of a distant galaxy called NGP–190387 by using the Atacama Large Millimetre/submillimetre Array, or ALMA, radio telescope.
Since stars expel the elements they form inside their cores as they reach the end of their lives, the discovery implies that the stars that created the fluorine must have lived and died quickly, researchers note.
According to their findings, published Thursday in the journal Nature Astronomy, the team believes that Wolf–Rayet stars — very massive stars that live only a few million years — are most likely the main producers of fluorine.
“We have shown that 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 joked.
Because the galaxy is so far away and because it takes so long for its light to reach Earth, what astronomers are seeing is actually what the star looked like 12 billion years ago, or when the universe was only about 1.4 billion years old. Never before had fluorine been observed in a star-forming galaxy so early in the history of the universe, researchers noted.
Other types of stars have been credited with fluorine production, but Franco’s team believes those processes, some of which take billions of years to take place, may not fully explain the amount of fluorine found in the galaxy in which the observed Wolf-Rayet star was located.
“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,” Chiaki Kobayashi, a professor at the University of Hertfordshire in England, said in a statement.
“This was a totally unexpected result,” she added. “Our measurement adds a completely new constraint on the origin of fluorine, which has been studied for two decades.”
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