The origin of fluorine is in young galaxies in the early universe

Like all the elements that exist on Earth, fluorine also has a cosmic origin. Now, a long-published article in the scientific journal Nature Astronomy, sheds some light on that

James Gitch" Professor of Astrophysics and Royal Society Research Fellow, University of Hertfordshire

[Translation by Dr. Moshe Nachmani]

If you look at the ingredients that appear on the toothpaste tube, you will probably come across a sentence like: "contains sodium fluoride". Fluoride, as we all know, is an important substance for the health of our teeth. The material strengthens the vitreous of the teeth, that hard protective layer that is around the tooth, thus it helps prevent 'holes in the teeth'.  

Basically, all the elements in nature were created long ago in the history of the universe. Hydrogen is the oldest element; It was created immediately after the 'big bang', about 13.7 billion years ago. Within minutes after this moment, the lightweight elements helium, deuterium and lithium were also created in a process called 'big bang nucleosynthesis'. Since then, almost all of the other elements have been formed by processes involving the birth and death of stars. However, these stars were not always around. Researchers still don't know exactly when the first stars formed in the universe, but it probably didn't happen during the hundred million years immediately after the Big Bang. Before that, the universe was full of hydrogen, along with the mysterious and invisible stuff that astronomers call 'dark matter'. This doc was not really even, but rough - and a little heavier in different places. These were the same areas that began to contract, or "collapsed", due to the force of gravity, while creating new galaxies. In places where the gas was not compressed enough, stars began to form while illuminating the universe. 

The billions of years that followed were a period of rapid growth: the rate of star formation in the universe increased sharply until it peaked ten billion years ago. Since then, the overall rate of star formation in the universe has been decreasing. That's why astronomers are so interested in understanding the early stages of the universe's formation: what happened then shaped what we see today. Although we have quite a lot of information regarding the way galaxies develop in terms of the formation of stars in them, we have relatively little insight regarding their chemical development in ancient times. These insights are important in light of the fact that when the stars are born or die, the elements they created are scattered throughout the galaxy and beyond. Many years later, some of these elements can form new planets like ours. 

As part of the research, the researchers discovered a distant galaxy called NGP-190387 with the help of a telescope that detects light with a wavelength of about a single millimeter. This study allowed scientists to observe light emitted from cold dust/gas in distant galaxies. The data revealed an unexpected finding: the omission of the emission of light at a wavelength of exactly 1.32 millimeters. This wavelength corresponds precisely to the wavelength at which the hydrogen-fluoride (HF) molecule, consisting of one hydrogen atom and one fluorine atom, absorbs light (taking into account the shift of the wavelength due to the expansion of the universe). The omission of this wavelength suggests the presence of a gaseous cloud composed of hydrogen fluoride in the galaxy. In light of this, it took 12 billion years to reach us on Earth, and thus we see the galaxy as it was when the universe was 1.4 billion years old.

This finding is interesting in light of the fact that it provides information regarding the galaxies becoming rich in chemical elements immediately after their formation. We were able to see that even at this early age, the distant galaxy (NGP-190387) has a high concentration of fluorine. Although we have observed other elements in distant galaxies, such as carbon, nitrogen and oxygen, this is the first time we have ever measured fluorine in a star-forming galaxy this far away. The more we observe a wider variety of elements in early galaxies, the better will be our understanding of the process of enrichment of chemical elements in that era.

We know that fluorine can be produced in several ways: for example, in supernova type star explosions, as well as in other red supergiant type stars that are at the end of their lives after burning most of the hydrogen and helium that were inside them. Models that focus on how elements are formed in stars and supernovae can tell us how much fluorine is expected to be in these sources. To our surprise, we discovered that the fluorine concentration was too great in the distant galaxy (NGP-190387) in light of the supernova explosion explanation alone. We had to find where the extra quantity came from, and the most logical explanation was that the source of this quantity is another type of star - a Wolf-Rayet star. Stars of this type are quite rare - there are only hundreds of units of stars of this type that have been classified for the Milky Way. But these are huge stars. Wolf-ray stars are a stage in the life cycle of extremely heavy stars - when their mass is ten times greater than that of the Sun. At the end of their short lives, these stars burn helium in their cores, and are millions of times brighter than our Sun. Typically, stars of this type have lost their outer layer of hydrogen due to powerful hydrogen winds, exposing the core of helium. Eventually, these stars will explode in a dramatic supernova explosion. When we add the amount of fluorine expected to come from Wolf-view stars to our model, we can eventually arrive at the correct amount related to the light emitted by the galaxy NGP-190387.

This finding adds to the growing body of evidence showing that the growth of galaxies was surprisingly rapid in the early universe. These processes, which caused the enrichment of the chemical elements in the universe, are the basis of the universe we see around us today, and this research provides new insight into the details of the astrophysics that governs our universe, the one that began as early as 12 billion years ago.     

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