The discovery of fluorine in an early galaxy could shed light on the chemical evolution of the early Universe.
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Fluorine is an important chemical element for humanity. In the form of fluoride, it is a naturally occurring mineral that is an important element of our bones and teeth.
Fluoride has been added to toothpaste and water supplies to strengthen our teeth and has been shown to assist in bone growth and recovery.
Now, a new discovery may have revealed where fluorine was forged in the early Universe. Using the Atacama Large Millimeter/submillimeter Array (ALMA) located in Northern Chile, a team of astronomers has found traces of fluoride in a distant star-forming galaxy.
In a paper published in the journal Nature Astronomy the authors explain that until recently, despite astronomers having some success in detecting fluorine in early stars, researchers were still debating where fluorine is produced.
Suspects for fluorine production currently include asymptotic giant branch stars, the ν-process in core-collapse supernovae, and Wolf–Rayet stars. These stars vary widely in both mass and lifespans.
Discovering fluorine in galaxies at great distances and thus at high redshifts could reveal how fluorine was produced in massive galaxies and could in turn teach astronomers more about how the Universe’s chemical contents evolved.
How Are Elements Created?
Forming shortly after the big bang, hydrogen was the first and simplest chemical element. Containing a single proton orbited by a single electron, it is still the Universe’s most abundant element.
Forming shortly after this was helium, deuterium — heavy hydrogen with a neutron joining the proton in the atomic nucleus — and lithium. The other heavier still elements would form in massive nuclear furnaces of gravitational bound hydrogen and helium, which we know now as stars.
Stars were created in the early Universe, around 100 million years after the rapid expansion we call the big bang, when overdense regions in the sea of hydrogen and helium collapsed in galaxies. In these areas, where this sea of gas was hot and dense enough, stars were born.
After billions of years this first generation of stars died; running out of fuel to sustain nuclear fusion and protect against gravitational collapse, they ended their lives in supernova explosions. The cosmic blasts dispersed heavier elements throughout the Universe.
These seeded elements would then go on to become the material from which the next generation of stars formed.
Astronomers refer to any chemical elements heavier than helium and hydrogen as “metals.” The first generation of stars were metal-poor, containing just traces of lithium. The generations of stars that came later would be increasingly rich in these metals.
Star formation hit its peak when the Universe was about 3.5 billion years old, with star birth rates declining since this point between 8 and 10 billion years ago. Astronomers want to know what happened at this point, as it could provide a vital clue as to why the Universe around us takes the shape it does today.
This includes discovering how the heavy elements were created and dispersed, including fluorine.
Observing An Early Galaxy
A team of astronomers, including Maximilien Franco from the University of Hertfordshire in the UK, studied the high redshift galaxy NGP–190387. We see this galaxy as it was when the Universe was just 1.4 billion years old, roughly 10 percent of its current age.
Because stars expel the elements they form in their cores as they reach the end of their lives, the detection of fluorine in such an early galaxy may indicate that the stars that were the birthplace of fluorine must have lived and died quickly.
The more massive a star is, the quicker it burns through its fuel and reaches the end of its lifetime. That means that the team’s findings indicate that fluorine must form in the most massive of stars.
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Fitting this description are Wolf Reyet stars, incredibly massive stars that live for just millions of years, and the probable creation points of fluorine. While millions of years may seem like an incomprehensibly long time for us, it is a mere blink of an eye in cosmic terms and for the average star.
Wolf Rayet stars had been suspected as fluoride creators before, but previous research had failed to consider just how important these stars could be.
Of the other suspected fluoride creating stars, the researchers believe that the pulsations of giant evolved stars with several times the mass of our sun called asymptotic giant branch stars cannot account for the abundance of fluorine they detected in NGP–190387.
NGP–190387 displays fluorine amounts similar to those observed in the Milky Way, which is 13.5 billion years old but must have reached these levels incredibly quickly.
The discovery is an exciting one for astronomers as it has been found previously in distant and early quasars, and in active galactic nuclei powered by feeding supermassive black holes, but never in a star-forming galaxy that existed so early in the Universe.
Follow-up studies of NGP–190387 will likely involve the Extremely Large Telescope (ELT), currently under construction in the Atacama desert region of Northern Chile.
The team hopes this will reveal further secrets held by this early region of star formation, including the kind of stars it harbors.
Franco. M., Coppin. K. E. K., Geach. J. E., et al, , ‘The ramp-up of interstellar medium enrichment at z > 4,’ Nature Astronomy, [https://www.nature.com/articles/s41550-021-01515-9]