# Are sulfur and phosphorus also created in the nucleosynthesis of big stars?

There are as far as I know two fusion reactions by which stars convert hydrogen to helium: The CNO cycle (for carbon-nitrogen-oxygen) and the proton-proton chain reaction. The elements created in the CNO cycle are C,N,O and Fluor. But in this video min:13:00 https://www.youtube.com/watch?v=pxrPaNDvaQE the prof. talks about Phosphorus and sulfur. Is that true and are those element also created in the CNO cycle or is he talking about something else?

Yes, they are created through stellar nucleosynthesis.

Sulfur is created from silicon via an alpha process, with the reaction $$_{14}^{28} ext{Si }+ ext{ } _2^4 ext{He} o _{16}^{32} ext{S }+gamma$$ Oxygen burning can also create $_{16}^{31} ext{S}$, as well as other elements like $_{15}^{31} ext{P}$. Additionally, both oxygen and phosphorus can be formed through supernova nucleosynthesis (see Koo et al. (2013)).

The CNO cycle won't produce sulfur or phosphorus. The chain simply isn't set up to create either of them directly.

It is not true to say that the CNO cycle produces these elements. It is more like a catalytic chain that aids the conversion of hydrogen to helium. Thus pre-existing CNO nuclei are required and all the reactions do is change the balance of these elements because the reaction steps in the chain have differing timescales.

Sulphur is mainly produced by alpha capture (fusion) onto. carbon and oxygen via neon, magnesium and silicon. This requires the high temperatures found near the cores of massive stars (more than 8 solar masses) and occurs fairly late in their lives, not long before the type II supernova that casts a lot of the processed material into space.

Phosphorus is not part of this "alpha chain" (https://en.m.wikipedia.org/wiki/Alpha_process) because its mass number is not divisible by 4 and it has an odd atomic number. However, it is also expected to be produced in massive stars via neutron capture onto isotopes of silicon (see https://arxiv.org/abs/1112.3824 ). This occurs in the neon and oxygen burning shells, late in the lives of massive stars.

## Star Stuff? Try “Big Bang Stuff!”

One of the (deservedly) frequently quoted observations by my hero Carl Sagan is that we are all star-stuff. The chemical elements in our bodies – and everything we see around us on Planet Earth – were forged in exploding stars billions of years ago. This is a profound realization. It seems to me that doesn’t go far enough, however.

I started thinking about the origins of the elements in our bodies, and made a connection I haven’t seen elaborated before. To explain myself, I have to explain the origin of the universe first.

The 98 elements that occur in nature are divided up by astronomers into two groups: hydrogen and helium, and “metals:” all the other stuff. Hydrogen and helium were the products of the evolution of matter following the big bang. The “metals” were subsequently produced in a process dubbed nucleosynthesis: nuclear fusion taking place within stars (the process was worked out over half a century ago the landmark paper is E. M. Burbidge, G. R. Burbidge, W. A. Fowler, F. Hoyle. 1957. Synthesis of the Elements in Stars, Rev. Mod. Phys. 29: 547). The proportions of these things are considered very important. The ration of hydrogen to helium in the observable universe is one of the hallmark tests for cosmology and models of the origins of the universe. Different models predict different ratios, and only the natural ration of about 76% hydrogen to 24% helium gets to decide which models fly.

The other stuff is used to characterize stars, with a measure called metallicity – the proportion of the stuff of the star that is not hydrogen or helium. For example, the metallicity of the sun is approximately 1.8% by weight. Put the other way, the sun is 98.2% hydrogen+helium by weight. This quantity is very helpful to astronomers as it’s a measure of the age of stars, among other things. The older the star, the higher the expected metallicity, as the metals are added by the very process of fusion. Looked at one way, it’s stellar pollution.

This started me thinking about human metallicity. There’s a nice summary on Wikipedia on the elemental composition of the human body (http://en.wikipedia.org/wiki/Composition_of_the_human_body). Here are the top ten elements and the percentage of the body, by weight and atomic proportion, that they represent:

• Oxygen – 65% by weight but 24% by atomic proportion
• Carbon – 18% by weight but 12% by atomic proportion
• Hydrogen – 10% by weight but 63% by atomic proportion (!!)
• Nitrogen – 3% by weight but 0.58% by atomic proportion
• Calcium – 1.4% by weight but 0.24% by atomic proportion
• Phosphorus – 0.78% by weight but 0.14% by atomic proportion
• Potassium – 0.25% by weight but 0.033% by atomic proportion
• Sulfur – 0.25% by weight but 0.038% by atomic proportion
• Sodium – 0.15% by weight but 0.037% by atomic proportion
• Chlorine – 0.15% by weight but 0.024% by atomic proportion

Ok, so what, I hear you say. Well, look at #3 in this list – hydrogen. Ten percent of our body mass is hydrogen, in chemical compounds like water, sugars, and all sorts of other things. However, two facts about hydrogen are important. First, it’s the lightest element there is, so 10% by weight is a big number by atoms. Second, hydrogen was not made by nucleosynthesis. It was made by the Big Bang itself – and sixty-three percent of the atoms in our bodies are hydrogen.

If we shift our attention away from overall proportions by mass and re-list things by number of atoms, we see a different picture of our own composition. Yes, we are star-stuff – but 63% of the atoms in our bodies have their origins in the Big Bang itself. These humble hydrogen atoms that are the majority population in our bodies – and are the most abundant stuff in the visible universe – went through stars that exploded, but they came from the Big Bang. In a real sense, so did we.

## Title: DETECTION OF PHOSPHORUS, SULPHUR, AND ZINC IN THE CARBON-ENHANCED METAL-POOR STAR BD+44 493

The carbon-enhanced metal-poor star BD+44°493 ([Fe/H] = −3.9) has been proposed as a candidate second-generation star enriched by metals from a single Pop III star. We report the first detections of P and S and the second detection of Zn in any extremely metal-poor carbon-enhanced star, using new spectra of BD+44°493 collected by the Cosmic Origins Spectrograph on the Hubble Space Telescope . We derive [P/Fe] = −0.34 ± 0.21, [S/Fe] = +0.07 ± 0.41, and [Zn/Fe] = −0.10 ± 0.24. We increase by 10-fold the number of Si i lines detected in BD+44°493, yielding [Si/Fe] = +0.15 ± 0.22. The [S/Fe] and [Zn/Fe] ratios exclude the hypothesis that the abundance pattern in BD+44°493 results from depletion of refractory elements onto dust grains. Comparison with zero-metallicity supernova (SN) models suggests that the stellar progenitor that enriched BD+44°493 was massive and ejected much less than 0.07 M of Ni, characteristic of a faint SN.

## Are sulfur and phosphorus also created in the nucleosynthesis of big stars? - Astronomy

Sulfur is the second element in the sixteenth column of the periodic table. It is classified as a nonmetal. Sulfur atoms have 16 electrons and 16 protons with 6 valence electrons in the outer shell. Sulfur is the tenth most abundant element in the universe.

Sulfur can take the form of over 30 different allotropes (crystal structures). This is the most allotropes of any element.

Characteristics and Properties

Under standard conditions sulfur is a pale yellow solid. It is soft and odorless. The most common allotrope of sulfur is called octasulfur.

Sulfur does not dissolve in water. It also works as a good electrical insulator.

When burned, sulfur emits a blue flame and melts into a molten red liquid. It also combines with oxygen to form a toxic gas called sulfur dioxide (SO2).

Sulfur forms many different compounds including the gas hydrogen sulfide which is famous for having the strong odor of rotten eggs. Hydrogen sulfide is dangerous as it is flammable, explosive, and highly poisonous.

Where is sulfur found on Earth?

Elemental sulfur can be found in a number of areas on Earth including volcanic emissions, hot springs, salt domes, and hydrothermal vents.

Sulfur is also found in a number of naturally occurring compounds called sulfides and sulfates. Some examples are lead sulfide, pyrite, cinnabar, zinc sulfide, gypsum, and barite.

Sulfur can be mined from underground deposits. It can also be recovered as a byproduct from various industrial processes including the refining of petroleum.

How is sulfur used today?

Sulfur and its compounds have a number of industrial applications. The majority of sulfur is used to make the chemical sulfuric acid. Sulfuric acid is the top chemical used by the world's industry. It is used to make car batteries, fertilizer, refine oil, process water, and to extract minerals.

Other applications for sulfur based chemicals include the vulcanization of rubber, bleaching paper, and making products such as cement, detergents, pesticides. and gunpowder.

Sulfur also plays an important role in supporting life on Earth. It is the eighth most abundant element in the human body. Sulfur is part of the proteins and enzymes that make up our bodies. It is important in forming fats and strong bones.

How was it discovered?

Sulfur has been known about since ancient times. Ancient cultures in India, China, and Greece all knew about sulfur. It is even referred to in the Bible as "brimstone." Sometimes it is spelled "sulphur."

It was French chemist Antoine Lavoisier who, in 1777, proved that sulfur was one of the elements and not a compound.

Where did sulfur get its name?

Sulfur gets its name from the Latin word "sulphur" which is formed from a Latin root meaning "to burn."

There are four stable isotopes of sulfur including sulfur-32, 33, 34, and 36. The majority of naturally occurring sulfur is sulfur-32.

## The scientific story of how each element was made

“It is the function of science to discover the existence of a general reign of order in nature and to find the causes governing this order. And this refers in equal measure to the relations of man — social and political — and to the entire universe as a whole.” -Dmitri Mendeleev

There are over 100 elements in the periodic table, of which 91 are naturally found on Earth.

But at the moment of the Big Bang, none of them existed at all.

After the first second, quarks and gluons cooled to form bound states: protons and neutrons.

After three minutes, the hot Universe fused those nucleons into helium and a tiny bit of lithium, but no further.

After tens of millions of years, we finally formed the first stars, making additional helium.

Massive enough stars become giants, fusing helium into carbon, also producing nitrogen, oxygen, neon, and magnesium.

The most massive stars become supergiants, fusing carbon, oxygen, silicon, and sulphur, reaching the transition metals.

Giant and supergiant stars create free neutrons, which can build up nuclei all the way to lead/bismuth.

Most supergiants go supernova, where fast neutrons get absorbed, reaching uranium and beyond.

Neutron star mergers create the greatest heavy element abundances of all, including gold, mercury, and platinum.

Meanwhile, cosmic rays blast nuclei apart, creating the Universe’s lithium, beryllium, and boron.

Finally, the heaviest, unstable elements are made in terrestrial laboratories.

The result is the rich, diverse Universe we inhabit today.

At last, each element’s primary origin is known.

Mostly Mute Monday tells an astronomical story about an object or phenomenon in this Universe is pictures, visuals and no more than 200 words.

## Abundance of the chemical elements

The abundance of the chemical elements is a measure of the occurrence of the chemical elements relative to all other elements in a given environment. Abundance is measured in one of three ways: by the mass-fraction (the same as weight fraction) by the mole-fraction (fraction of atoms by numerical count, or sometimes fraction of molecules in gases) or by the volume-fraction. Volume-fraction is a common abundance measure in mixed gases such as planetary atmospheres, and is similar in value to molecular mole-fraction for gas mixtures at relatively low densities and pressures, and ideal gas mixtures. Most abundance values in this article are given as mass-fractions.

For example, the abundance of oxygen in pure water can be measured in two ways: the mass fraction is about 89%, because that is the fraction of water's mass which is oxygen. However, the mole-fraction is about 33% because only 1 atom of 3 in water, H2O, is oxygen. As another example, looking at the mass-fraction abundance of hydrogen and helium in both the Universe as a whole and in the atmospheres of gas-giant planets such as Jupiter, it is 74% for hydrogen and 23–25% for helium while the (atomic) mole-fraction for hydrogen is 92%, and for helium is 8%, in these environments. Changing the given environment to Jupiter's outer atmosphere, where hydrogen is diatomic while helium is not, changes the molecular mole-fraction (fraction of total gas molecules), as well as the fraction of atmosphere by volume, of hydrogen to about 86%, and of helium to 13%. [Note𔀳]

The abundance of chemical elements in the universe is dominated by the large amounts of hydrogen and helium which were produced in the Big Bang. Remaining elements, making up only about 2% of the universe, were largely produced by supernovae and certain red giant stars. Lithium, beryllium and boron are rare because although they are produced by nuclear fusion, they are then destroyed by other reactions in the stars. [1] [2] The elements from carbon to iron are relatively more abundant in the universe because of the ease of making them in supernova nucleosynthesis. Elements of higher atomic number than iron (element 26) become progressively rarer in the universe, because they increasingly absorb stellar energy in their production. Also, elements with even atomic numbers are generally more common than their neighbors in the periodic table, due to favorable energetics of formation.

The abundance of elements in the Sun and outer planets is similar to that in the universe. Due to solar heating, the elements of Earth and the inner rocky planets of the Solar System have undergone an additional depletion of volatile hydrogen, helium, neon, nitrogen, and carbon (which volatilizes as methane). The crust, mantle, and core of the Earth show evidence of chemical segregation plus some sequestration by density. Lighter silicates of aluminum are found in the crust, with more magnesium silicate in the mantle, while metallic iron and nickel compose the core. The abundance of elements in specialized environments, such as atmospheres, or oceans, or the human body, are primarily a product of chemical interactions with the medium in which they reside.

## We Are Stardust

In a previous article, I gave a brief look at the reality of our unremarkable place in the Universe. I also mentioned the possibility—even the likelihood—that our universe is only one among billions or trillions of universes and that, if correct, such a picture of a mega-vast cosmos would be an explanation of sorts to the existence in these parts of physical constants and conditions amenable to the emergence of life. We would be living in a rare, Goldilocks realm, because of a statistical fact. Among so many bubbles of energy, it is not odd that at least one would make possible life as we know it.

We do know for sure that there is at least one species of living beings with enough awareness to ask fundamental questions about reality, and with the ability to propose plausible answers which they in turn test by experiments and observations. In short, they are capable of doing what we call science.

Many people express their resistance to the fact that we are merely material, made up of “stuff.” The idea that there’s more to humans, in the form of “souls” or “spirits,” is endemic to the religious among us, who often conceive a realm for the material, this “vale of tears,” and one destined for “souls”—which in turn consists basically of two imaginary places: one for the damned, “hell,” one for the rewarded, “heaven.” Religious dogmas have the pretension of explaining it all, ending up explaining nothing. Since the 17 th century, what we now call the Scientific Revolution began to supplant non-explanations and bad explanations with good explanations.

Science, an international and intergenerational enterprise, has figured out that our bodies are made up mostly of four chemical elements: carbon, hydrogen, oxygen and nitrogen (CHON). We are 96 percent CHON, mostly water, a compound of hydrogen and oxygen. As kids already know by the fourth grade or so, each molecule of water is made up of two atoms of hydrogen and one atom of oxygen. The rest of the stuff in us includes elements like sulphur, calcium, potassium, iodine, phosphorus, iron, and so forth. All those raw materials are assembled in complex organic molecules (“organic” as in carbon-based, mostly in what we call proteins), of which the most essential is DNA (deoxyribonucleic acid, carrier of the genetic code).

Where do all those elements come from? Hydrogen, the “H” in CHON, was made in abundance during the first instant of the Universe, the so-called Big Bang. Observations of the oldest stars in the known universe have shown that they are made up exclusively of hydrogen and helium (He, the second element in the Periodic Table, also made mostly during the Big Bang, through the fusion of hydrogen nuclei in a process known as Big Bang nucleosynthesis). Second-generation stars like the sun are still made up mostly of hydrogen and helium, but also contain traces of heavier elements, which were in turn the product of nuclear fusion that took place inside stars (a process known as stellar nucleosynthesis).

Stellar nucleosynthesis is capable of producing elements heavier than hydrogen and helium, up to iron. To produce nuclei heavier than iron, a remarkable event is required, a supernova, because of the enormous amount of energy needed to produce heavier elements through nuclear fusion. A supernova is an exploding star, whose energy output is so huge that for weeks its light is brighter than that of the hundreds of billions of stars present in the same galaxy. Upon their explosions, supernovae scatter atomic material—the elements, up to iron, heavier than H and He—through space, while the heat and energy of the explosion yields elements heavier than iron (including silver, gold, and uranium). All that material often mixes with interstellar clouds of hydrogen and helium, which coalesce due to gravity to form new stars. Our nearest star, the sun, is the product of such a process.

Some of that stuff scattered by those explosions ended up in our bodies, mostly in the form of CON (without the H, which was made much earlier when our universe was just appearing) which, not surprisingly, are the most common of the nuclei heavier than hydrogen and helium present in the Universe. Life is “pragmatic” and made use of the raw materials that were available. As Astrophysicist John Gribbin put it, “it can hardly be a coincidence that carbon, nitrogen, and oxygen are among the more abundant products of nucleosynthesis inside the stars.”

That is the origin of the iron present in our hemoglobin. It came from the stars. There is a basic kinship between stars and humans. We are stardust, as American astronomer Carl Sagan was fond of reminding us. All those atoms present in our bodies are also “energy,” which materialized in line with the relationship between matter and energy, as first proposed by Albert Einstein in 1905, his Annus Mirabilis. The energetic event that produced quarks, electrons, neutrinos and electromagnetic radiation (light, from the more energetic gamma rays to visible light to radio and micro waves) was the Big Bang. The quarks in turn formed protons and neutrons, which ended up assembled in the nuclei of atoms. Given the conditions of energy, temperature and pressure present in those nuclear furnaces we call stars, many of those nuclei fuse with others to yield atoms heavier than hydrogen and helium.

The most important contributor to the theoretical aspect of nucleosynthesis, which has been confirmed by observations, was English Physicist Fred Hoyle. Hoyle’s maverick ways may have cost him a Nobel Prize, but he is regarded as a great scientist who deserved more recognition when he was alive. His contributions to the understanding of Big Bang and stellar nucleosynthesis speak for themselves.

Given all this, I do not mind being made up of “stuff” (“star stuff,” as it turned out). Mythological stories (think, for instance, of the Judeo-Christian, infantile creation myth or the unimpressive “burning bush” at Mount Sinai) pale in comparison with the wonders of the Universe.

## Are sulfur and phosphorus also created in the nucleosynthesis of big stars? - Astronomy

The Universe is now 1 minute old, and all the anti-matter has been destroyed by annihilation with matter. The leftover matter is in the form of electrons, protons and neutrons. As the temperature continues to drop, protons and neutrons can undergo fusion to form heavier atomic nuclei. This process is called nucleosynthesis.

Its harder and harder to make nuclei with higher masses. So the most common substance in the Universe is hydrogen (one proton), followed by helium, lithium, beryllium and boron (the first elements on the periodic table). Isotopes are formed, such as deuterium and tritium, but these elements are unstable and decay into free protons and neutrons.

Note that this above diagram refers to the density parameter, />, of baryons, which is close to 0.03. However, much of the Universe is in the form of dark matter, which brings the value of />M to 0.3.

A key point is that the ratio of hydrogen to helium is extremely sensitive to the density of matter in the Universe (the parameter that determines if the Universe is open, flat or closed). The higher the density, the more helium produced during the nucleosynthesis era. The current measurements indicate that 75% of the mass of the Universe is in the form of hydrogen, 24% in the form of helium and the remaining 1% in the rest of the periodic table (note that your body is made mostly of these `trace' elements). Note that since helium is 4 times the mass of hydrogen, the number of hydrogen atoms is 90% and the number of helium atoms is 9% of the total number of atoms in the Universe.

There are over 100 naturally occurring elements in the Universe and classification makes up the periodic table. The very lightest elements are made in the early Universe. The elements between boron and iron (atomic number 26) are made in the cores of stars by thermonuclear fusion, the power source for all stars.

The fusion process produces energy, which keeps the temperature of a stellar core high to keep the reaction rates high. The fusing of new elements is balanced by the destruction of nuclei by high energy gamma-rays. Gamma-rays in a stellar core are capable of disrupting nuclei, emitting free protons and neutrons. If the reaction rates are high, then a net flux of energy is produced.

Fusion of elements with atomic numbers (the number of protons) greater than 26 uses up more energy than is produced by the reaction. Thus, elements heavier than iron cannot be fuel sources in stars. And, likewise, elements heavier than iron are not produced in stars, so what is their origin?.

--> The construction of elements heavier than Fe (iron) involves nucleosynthesis by neutron capture. A nuclei can capture or fuse with a neutron because the neutron is electrically neutral and, therefore, not repulsed like the proton. In everyday life, free neutrons are rare because they have short half-life's before they radioactively decay. Each neutron capture produces an isotope, some are stable, some are unstable. Unstable isotopes will decay by emitting a positron and a neutrino to make a new element.

Neutron capture can happen by two methods, the s and r-processes, where s and r stand for slow and rapid. The s-process happens in the inert carbon core of a star, the slow capture of neutrons. The s-process works as long as the decay time for unstable isotopes is longer than the capture time. Up to the element bismuth (atomic number 83), the s-process works, but above this point the more massive nuclei that can be built from bismuth are unstable.

The second process, the r-process, is what is used to produce very heavy, neutron rich nuclei. Here the capture of neutrons happens in such a dense environment that the unstable isotopes do not have time to decay. The high density of neutrons needed is only found during a supernova explosion and, thus, all the heavy elements in the Universe (radium, uranium and plutonium) are produced this way. The supernova explosion also has the side benefit of propelling the new created elements into space to seed molecular clouds which will form new stars and solar systems.

The last stage in matter production is when the Universe cools sufficiently for electrons to combine with the proton/neutron nuclei and form atoms. Constant impacts by photons knock electrons off of atoms which is called ionization. Lower temperatures mean photons with less energy and fewer collisions. Thus, atoms become stable at about 15 minutes after the Big Bang.

These atoms are now free to bond together to form simple compounds, molecules, etc. And these are the building blocks for galaxies and stars.

Even after the annihilation of anti-matter and the formation of protons, neutrons and electrons, the Universe is still a violent and extremely active environment. The photons created by the matter/anti-matter annihilation epoch exist in vast numbers and have energies at the x-ray level.

Radiation, in the form of photons, and matter, in the form of protons, neutrons and electron, can interact by the process of scattering. Photons bounce off of elementary particles, much like billiard balls. The energy of the photons is transfered to the matter particles. The distance a photon can travel before hitting a matter particle is called the mean free path.

Since matter and photons were in constant contact, their temperatures were the same, a process called thermalization. Note also that the matter can not clump together by gravity. The impacts by photons keep the matter particles apart and smoothly distributed.

The density and the temperature for the Universe continues to drop as it expands. At some point about 15 minutes after the Big Bang, the temperature has dropped to the point where ionization no longer takes places. Neutral atoms can form, atomic nuclei surrounded by electron clouds. The number of free particles drops by a large fraction (all the protons, neutrons and electron form atoms). And suddenly the photons are free to travel without collisions, this is called decoupling.

The Universe becomes transparent at this point. Before this epoch, a photon couldn't travel more that a few inches before a collision. So an observers line-of-sight was only a few inches and the Universe was opaque, matter and radiation were coupled. This is the transition from the radiation era to the matter era.

The time of neutral atom construction is called recombination, this is also the first epoch we can observe in the Universe. Before recombination, the Universe was too dense and opaque. After recombination, photons are free to travel through all of space. Thus, the limit to our observable Universe is back in time (outward in space) to the moment of recombination.

The time of recombination is also where the linked behavior between photons and matter decouples or breaks, and is also the last epoch where radiation traces the mass density. Photon/matter collisions become rare and the evolution of the Universe is dominated by the behavior of matter (i.e. gravity), so this time, and until today, is called the matter era.

Today, radiation in the form of photons have a very passive role in the evolution of the Universe. They only serve to illuminate matter in the far reaches of the Galaxy and other galaxies. Matter, on the other hand, is free to interact without being jousted by photons. Matter becomes the organizational element of the Universe, and its controlling force is gravity.

Notice that as the Universe ages it moves to more stable elements. High energy radiation (photons) are unstable in their interactions with matter. But, as matter condenses out of the cooling Universe, a more stable epoch is entered, one where the slow, gentle force of gravity dominates over the nuclear forces of earlier times.

Much of the hydrogen that was created at recombination was used up in the formation of galaxies, and converted into stars. There is very little reminant hydrogen between galaxies, the so-called intergalactic medium, except in clusters of galaxies. Clusters of galaxies frequently have a hot hydrogen gas surrounding the core, this is leftover gas from the formation of the cluster galaxies that has been heated by the motions of the cluster members.

## Stars rich in phosphorus: seeds of life in the universe

The journal Nature Communications today is publishing the discovery of a new type of stars, very rich in phosphorus, which could help to explain the origin of this chemical element in our Galaxy. This achievement has been made by astronomers of the Instituto de Astrofísica de Canarias (IAC) and researchers in computer science from the Centre for Research in Information and Communication Technology (CITIC) at the University of La Coruña (Galicia).

All the chemical elements in the universe, except for hydrogen and most of the helium, were produced inside stars. But among them there are a few (carbon, nitrogen, oxygen, sulphur and phosphorus) which are particularly interesting because they are basic to life as we know it on Earth. Phosphorus is of special interest because it forms part of the DNA and RNA molecules and is a necessary element in the energetic interchange within cells, and for the development of their membranes.

The study published in Nature, based on an analysis of a large number of infrared spectra (in the H band, with APOGEE) from the public data base of the Sloan Digital Sky Survey, could offer a clear set of promising stellar candidates to clarify the origin and the quantity observed of phosphorus in the Galaxy, and specifically, in our Solar System, which until now none of the current models of Galactic chemical evolution have been able to explain.

However, the peculiar chemistry which these stars show is still disconcerting. In fact, not only are they rich in phosphorus, but also in certain other elements, such as magnesium, silicon, oxygen, aluminium and even of heavier elements such as cerium. Suprisingly, after an extensive analysis of all the possible stellar sources and processes known to form chemical elements in the interiors of stars, this chemical pattern is not predicted by the current theories of stellar evolution and nucleosynthesis.

"These results show that not only are we dealing with a new type of objects, but that their discovery opens the way for the exploration of new physical mechanisms and nuclear reactions which occur in stellar interiors" explains IAC researcher Thomas Masseron, the leader of the project and the first author of the article.

"It could be an important clue about the origin of the phosphorus, which is a fundamental component of life", says Aníbal García-Hernández, another IAC researcher, who is the second author of the article.

In addition, thanks to Spanish service time, they could obtain the optical spectrum of the most brilliant of the phosphorus stars with the Echelle spectrograph (FIES) on the Nordic Optical Telescope (NOT) at the Roque de los Muchachos Observatory, (Garafía, La Palma).

"This spectrum allowed us to obtain the chemical abundances of further elements in these stars which are peculiar and rich in phosphorus, and to rule out definitively any known stellar candidate which could explain the stars which are rich in this elements", indicates Olga Zamora, a co-author of the article, and an IAC support astronomer.

"A discovery which is so unexpected and extraordinary could not have been made without a close interdisciplinary collaboration between astronomers and experts in computation", points out Arturo Manchado, an IAC research and a co-author of the article.

## Supernovae: Exploding Stars

Supernovae are explosive events that result in the materials and gases of a star being flung far and wide into the interstellar medium, later going on to become future generations of new stars, planets, moons, and even living beings.

The process of creating the elements occurs in the heart of the star as it heads towards its last days - in a process known as stellar nucleosynthesis. This method is responsible for how many of the heavier elements that we see around us (including oxygen, carbon, calcium, nitrogen, phosphorus and more) are created, and is known as the slow-neutron capture process, or s-process.

Then when a supernova occurs, these newly created elements are dispersed out into the local region around the star, eventually coming together in a recycling process that forms the next generation of astrophysical objects.

Typically, supernovae fall into two major categories. The first describes when massive stars have reached the end of their life, having burned through all their fuel, fusing heavier elements until they get to iron.

By this point they can’t fuse these heavy isotopes, so they end up exploding into a supernova, leaving behind either a neutron star or a black hole. This type of supernovae is called Type II (or commonly referred to as the core-collapse model).

However, another type of supernova can occur, and this one is called a Type Ia, which is a little more complex. These supernovae are formed from a binary star system, where two stars orbit each other closely, with one of these stars being a white dwarf.

The compact, yet massive white dwarf can draw material from the other star in the system, accumulating its own mass. By itself, a white dwarf is a fairly stable star, but as it steals material from its companion it becomes larger and more massive.

Once the white dwarf has accumulated enough material to reach approximately 1.4 times the mass of the Sun (a mass known as the Chandrasekhar limit), it becomes hot enough and dense enough to trigger thermonuclear burning, causing the white dwarf to rapidly explode in a supernova event.

Additionally, sometimes two white dwarfs merge, which also trigger a type Ia supernova event.

“Different processes occur when stars end their lives. A Type Ia supernova occurs when a carbon-oxygen white dwarf - the remnant of a star with an initial mass less than a few times that of the sun - interacts with its binary companion, which can be another white dwarf or even a main sequence or helium star.”

“If enough mass is taken from the companion star by the ‘primary’ carbon-oxygen white dwarf, the star becomes hot and dense enough to begin fusing together carbon and oxygen at an explosive rate. Type Ia supernovae produce most of the ‘iron peak’ elements in the universe: elements like iron, nickel and also elements like chromium and vanadium, the interest of this paper,” she said.

Dr Panther emphasised the importance of looking beyond optical light to study nucleosynthesis.

“When we look at optical light, we can use spectral lines as a kind of fingerprint to see what sort of elements were made in a supernova explosion. However, this only tells you the name of the element.”

“When we study nucleosynthesis, we are usually interested in the amounts of different isotopes of elements that are formed as this tells us about the temperatures, densities and abundances of raw materials that were involved in nucleosynthesis.”

“The gamma-ray spectrum encodes information about the nuclear structure of an element, so it is a more accurate way of determining the ways in which nucleosynthesis occurs in a supernova,” she said.