Have a look at the components on a tube of toothpaste and you’ll in all probability learn one thing like “comprises sodium fluoride”. Fluoride, as you in all probability know, is essential for wholesome tooth. It strengthens enamel, the onerous, protecting layer round a tooth, and so helps stop cavities.
It’s possible you’ll not suppose too deeply about toothpaste. However like all issues on Earth, from the majestic to the mundane, fluoride – and the story of a smile – has a cosmic origin. Now, my colleagues and I’ve printed a paper in Nature Astronomy that sheds some mild on it.
Just about all pure components had been shaped way back within the historical past of the universe. Hydrogen is the oldest aspect: it shaped very shortly after the large bang, about 14 billion years in the past. Inside a couple of minutes of the large bang, the sunshine components helium, deuterium and lithium had been additionally shaped in a course of known as massive bang nucleosynthesis. Since then, practically each different aspect has been cast in processes related to the life and loss of life of stars. However these stars weren’t all the time round.
We nonetheless don’t know precisely when the primary stars ignited within the universe, however it in all probability didn’t occur for about 100 million years or so after the large bang. Earlier than this, the universe was crammed with a fog of hydrogen, mingled with the mysterious, invisible substance astronomers name darkish matter. This fog was not clean, however rippled – barely denser in some locations. It was these areas that began to contract, or “collapse”, as a consequence of gravity, to type the primary galaxies. The place the fuel obtained dense sufficient, stars ignited and lit up the universe.
The next few billion years was a time of fast development: the speed of star formation within the universe rose sharply till it reached a peak, 8 to 10 billion years in the past. Ever since that “cosmic midday”, the general fee of star formation within the universe has been in decline. That’s why astronomers are so within the early phases of the historical past of the cosmos: what occurred then formed what we see round us as we speak.
Whereas we have now numerous details about how the expansion of galaxies “ramped up” by way of their star formation, we have now comparatively little perception into their chemical evolution on the earliest instances. That is essential as a result of, as stars dwell and die, the weather they produce turn into dispersed all through a galaxy and past. A few years later, a few of these components can type new planets like ours.
We noticed a distant galaxy known as NGP-190387 with the Atacama Giant Millimetre/sub-millimetre Array (Alma) – a telescope that detects mild with a wavelength of round one millimetre. This permits us to see the sunshine emitted by chilly mud and fuel in distant galaxies. The info revealed one thing surprising: a dip within the mild at a wavelength of precisely 1.32 millimetres. This corresponds precisely to the wavelength at which the molecule hydrogen fluoride (HF), comprising a hydrogen atom and fluorine atom, absorbs mild (making an allowance for a shift in wavelength that occurs as a result of universe’s growth). The deficit of sunshine implies the presence of clouds of hydrogen fluoride fuel within the galaxy. This mild has taken over 12 billion years to succeed in us, and we see the galaxy because it was when the universe was 1.4 billion years outdated.
That is thrilling, as a result of it offers details about how galaxies first turned enriched with chemical components shortly after they first shaped. We will see that even at this early time, NGP-190387 had a excessive abundance of fluorine. Though we have now noticed different components in distant galaxies, corresponding to carbon, nitrogen and oxygen, that is the primary time fluorine has been detected in a star-forming galaxy at such a distance. The better the number of components we will observe in early galaxies, the higher our understanding of the method of chemical enrichment at the moment.
We all know that fluorine could be produced in several methods: for instance, in star explosions known as supernovas and in sure “asymptotic large department” stars – crimson supergiant stars nearing the top of their life, having burned a lot of the hydrogen and helium of their cores and now swollen in dimension.
Fashions of how components type in stars and in supernovae can inform us how a lot fluorine we must always anticipate from these sources. And we discovered that the abundance of fluorine was too excessive in NGP-190387 to be defined by supernovas and asymptotic large department stars alone. An additional supply was wanted, and that is in all probability one other sort of star known as a Wolf-Rayet. Wolf-Rayet stars are fairly uncommon – there are just a few hundred catalogued within the Milky Manner, for instance. However they’re excessive.
Wolf-Rayet stars are a section within the lifecycle of very huge stars – with greater than ten instances the mass of our Solar. Approaching the top of their brief life, these stars burn helium of their cores, and are hundreds of thousands of instances extra luminous than the Solar. Unusually, Wolf-Rayet stars have misplaced their envelope of hydrogen by way of highly effective winds, leaving the helium core uncovered. They are going to finally explode in dramatic core-collapse supernova explosions. After we added the quantity of fluorine anticipated from Wolf-Rayet stars to our mannequin, we might lastly account for the dip in mild from NGP-190387.
This provides to a rising physique of proof that exhibits that the expansion of galaxies was surprisingly fast-paced within the early universe: a frenzy of star formation and chemical enrichment. These processes lay the foundations for the universe we see round us as we speak, and this work offers new perception into the detailed astrophysics at play, over 12 billion years in the past.
However maybe the principle take away is that it exhibits that the story of your smile is a story as outdated as time.