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In the book "Horizons_ exploring the universe-Cengage learning (2018)", p200, it states that:
Helium fusion produces carbon, and some of the carbon nuclei absorb helium nuclei to form oxygen. A few of the oxygen nuclei can absorb helium nuclei and form neon and then magnesium.
But when I check Wikipedia for Oxygen-burning process, there doesn't seem to have any steps that will produce Neon, but when I check for Carbon-burning process, two carbon-12 nuclei can fuse to a neon and helium nuclei, so is there an error in the book? Or there are other steps of oxygen burning that will produce neon?
The pages you're looking at describe fusion of two similar nuclei with each other (e.g. oxygen with oxygen). But fusion doesn't have to involve identical nuclei, and reactions involving more abundant nuclei will in general occur at a higher rate (though this can vary based on other factors, too).
Long before oxygen-oxygen or neon-neon reactions become important, reactions involving helium nuclei (also called “alpha particles”) take place. That is what the text in your book is referring to: C + He gives O, and O + He gives Ne. See the list in this Wikipedia article on the alpha process.
University of California, San Diego Center for Astrophysics & Space Sciences
Nuclear energy can be produced by either of two types of reactions: fission, the splitting apart of a massive atomic nucleus, or by fusion of lighter nuclei into a heavier nucleus.
|proton||p +||+1||1.673 x 10 -24||1.00727||baryon|
|neutron||n 0||0||1.675 x 10 -24||1.00866||baryon|
|e - /e +||-1/+1||9.109 x 10 -28||5.485 x 10 -4||lepton|
|neutrino||0||< 10 -32||< 5 x 10 -9||lepton|
- How a nuclear fission reactor works.
- The Virtual Nuclear Tourist has a wealth of nuclear (fission) information, including sections on Chernobyl, Three-Mile Island, and environmental effects.
- Try your hand at controlling a nuclear reactor.
- The High Energy Weapons Archive and Trinity Site are sites with historical and current information about nuclear weapons.
- Two sites on Fusion Power from the Princeton Plasma Physics Laboratory and the Contemporary Physics Education Project
- Highly recommended reference: The Making of the Atomic Bomb" by Richard Rhodes - Pulitzer Prize winning account of the Manhattan Project. Also, "Dark Sun" - not quite as readable account of the development of Fusion Weapons by the same author.
The Proton-Proton Chain is the principal set of reactions for solar-type stars to transform hydrogen to helium:
- 1 H + 1 H --> 2 H + e + + neutrino Two protons (p + ) react to form Deuterium ( 2 H = 1p + & 1 n) plus a positron (e + ) and a neutrino. In the highly ionized stellar interior the positron will quickly "annihilate" with an electron (e + + e - --> 2 gamma-rays) the gamma-rays will be absorbed and re-emitted by the dense matter in the stellar interior, gradually diffusing outward and being "degraded" into photons of lower energy. When the gamma-ray energy reaches the photosphere each gamma-ray will have been transformed into about 200,000 visible photons. The neutrino, which only interacts through the Weak Force streams straight out of the sun.
The individual nuclear reactions proceed rather slowly, and it is a very small fraction of nuclei in the core of the sun with enough energy to overcome the electrical repulsion. Even so, every second the sun turns 600 million tons of hydrogen into 596 million tons of helium (with 4 million tons transformed into luminous eneryy via E=mc 2 ).
More massive stars burn hydrogen via a catalytic reaction called The CNO CYCLE. Because the initial step in the CNO Cycle requires a Carbon nucleus (6 p + ) to react with a proton it requires higher temperatures and is much more temperature sensitive than the P-P Chain (The energy produced is proportional to T 20 for the CNO cycle vs T 4 for the P-P Chain). Stars of mass greater than about 1.2 M with core temperatures, Tcore > 17 million K, produce most of their energy by the CNO cycle.
This reaction requires both very high temperatures (T > 100 million K) and very high densities which will occur only after the star has exhausted its store of hydrogen and has a core of nearly pure helium. Only stars with masses greater than about 0.4M will reach temperatures high enough to ignite the Triple-alpha process.
- Successive nuclear burning stages, involving more massive nuclei with higher charges, will require increasingly high temperatures to overcome the increased electrical repulsion.
- The amount of energy released by each successive reaction stage decreases so that later nuclear burning stages become shorter and shorter.
- Once fusion reactions have produced an iron core, further fusion reactions no longer produce energy, but absorb energy from the stellar core. As we shall see this may have a catastrophic effect on the star as it nears the end of its life.
Neutrinos were first "invented" by W. Pauli (of Exclusion Principle fame) in order to explain apparent failures in conservation of energy, momentum and leptons in certain nuclear decays. Pauli reasoned that these particles must be chargeless, have a mass much lower than the mass of the electron and interact only very weakly with other matter. He called them "neutrons", but when the massive baryon that we now call the neutron was discovered, it was realized that this could not be Pauli's particle and the name of the hypothetical particle was changed to "neutrino". The existence of the neutrino was confirmed by Reines and Cowan in 1956.
Although astrophysicists have great confidence in their calculations of the structure and evolution of stars like the sun, there is no substitute for experimental confirmation. Because the neutrinos are the only nuclear reaction products that make it out from the solar core, the most direct confirmation of the theories would be to measure the neutrinos emitted by the sun's P-P chain. The first experiment, begun in 1970 used a 100,000 gallon tank of cleaning fluid called perchloroethylene -- C2Cl4 to detect neutrinos from a subsidiary branch of the Proton-Proton Chain via the weak interaction:
The experiment was placed a mile underground in the Homestake gold mine in Lead, SD to avoid contamination from other particle interactions. The experiment was predicted to create 3 Argon atoms, which could be counted by their radioactivity, every other day, but only about 1/3 that number were detected. The experiment has continued for over 20 years and has recently been joined by other solar neutrino experiments in Japan (Kamiokande), Russia (SAGE = Soviet(sic)-American Gallium Experiment) and Italy (GALLEX), all reporting the same result.
The most promising resolution of this problem lies in the physics of the neutrino itself. There are three flavors of leptons -- electrons (with their associated anti-particle the positron), muons and tau leptons, each with an associated flavor of neutrino, , and . In an extension of the electroweak unified force theory it has been proposed that neutrinos can "oscillate" among these three flavors. If this theory is correct, then the electron neutrinos produced by the solar nuclear fusion reactions may be oscillating among flavors as they travel toward earth, producing the apparent deficit. One implication of this idea is that neutrinos must have a small but non-zero mass. Current limits place the mass of the electron neutrino at less than 1/100000 th the mass of the electron. Recent experimental results appear to confirm this theory.
- In a book entitled Telephone Poles and other Poems, John Updike published a poem about neutrinos called Cosmic Gall
- A comprehensive Neutrino History
- UC Irvine physicists report of detection of neutrino oscillations & mass from Kamiokande.
- Here is an account of the Solar Neutrino Problem relayed by John Bahcall and Ray Davis who have been involved since the beginning.
- Here are links to almost certainly more than you want to know.
Prof. H. E. (Gene) Smith
CASS 0424 UCSD
9500 Gilman Drive
La Jolla, CA 92093-0424
Last updated: 16 April 1999
- One of best studied supernova remnants is the Crab Nebula
About 1800 pc (or about 5900 light-years) from Earth with an angular diameter about one-fifth of the moon
Explosion appeared in sky in 1054
So brilliant ancient Chinese and Middle Eastern astronomers reported its brightness exceeded that of Venus
- If M<3M SUN , degenerate-neutron pressure will hold up weight of star.
1st pulsar discovered in 1968 by Jocelyn Bell, Cambridge U. (England) graduate student.
All our cards are on the table now. In principle, my task to introduce the basic concepts of Astrophysics is over. From here on, we’ll be playing with these concepts to understand the life of stars. We started with the basic question: What is Astrophysics? We covered the EM spectrum, Stefan’s law, concept of magnitude, classification of stars, Saha’s equation, the structure of Sun and most importantly, the Hertzsprung Russell diagram. Juggling with these concepts, we are now ready to study stellar evolution in the next articles. Stay tuned!
16 thoughts on &ldquoNuclear Reactions In Stars&rdquo
Waoh, this article is JUST AMAZING!!
Nuclear physics, chemistry and astrophysics ❤️ makes me very happy
Scientists capture neon in an organic environment for the first time
In a new study, researchers from the Cambridge Crystallographic Data Centre (CCDC) and the U.S. Department of Energy's (DOE's) Argonne National Laboratory have teamed up to capture neon within a porous crystalline framework. Neon is well known for being the most unreactive element and is a key component in semiconductor manufacturing, but neon has never been studied within an organic or metal-organic framework until now. The results, which include the critical studies carried out at the Advanced Photon Source (APS), a DOE Office of Science user facility at Argonne, also point the way towards a more economical and greener industrial process for neon production. Neon is an element that is well-known to the general public due to its iconic use in neon signs, especially in city centres in the United States from the 1920s to the 1960s. In recent years, the industrial use of neon has become dominated by use in excimer lasers to produce semiconductors. Despite being the fifth most abundant element in the atmosphere, the cost of pure neon gas has risen significantly over the years, increasing the demand for better ways to separate and isolate the gas.
During 2015, CCDC scientists presented a talk at the annual American Crystallographic Association (ACA) meeting on the array of elements that have been studied within an organic or metal-organic environment, challenging the crystallographic community to find the next and possibly last element to be added to the Cambridge Structural Database (CSD). A chance encounter at that meeting with Andrey Yakovenko, a beamline scientist at the Advanced Photon Source, resulted in a collaborative project to capture neon -- the 95th element to be observed in the CSD.
Neon's low reactivity, along with the weak scattering of X-rays due to its relatively low number of electrons, means that conclusive experimental observation of neon captured within a crystalline framework is very challenging. In situ high pressure gas flow experiments performed at X-Ray Science Division beamline 17-BM at the APS using the X-ray powder diffraction technique at low temperatures managed to elucidate the structure of two different metal-organic frameworks with neon gas captured within the materials.
"This is a really exciting moment representing the latest new element to be added to the CSD and quite possibly the last given the experimental and safety challenges associated with the other elements yet to be studied" said Peter Wood, Senior Research Scientist at CCDC and lead author on the paper published in Chemical Communications. "More importantly, the structures reported here show the first observation of a genuine interaction between neon and a transition metal, suggesting the potential for future design of selective neon capture frameworks."
The structure of neon captured within the framework known as NiMOF-74, a porous framework built from nickel metal centres and organic linkers, shows clear nickel to neon interactions forming at low temperatures significantly shorter than would be expected from a typical weak contact.
Andrey Yakovenko said "These fascinating results show the great capabilities of the scientific program at 17-BM and the Advanced Photon Source. Previously we have been doing experiments at our beamline using other much heavier, and therefore easily detectable, noble gases such as xenon and krypton. However, after meeting co-authors Pete, Colin, Amy and Suzanna at the ACA meeting, we decided to perform these much more complicated experiments using the very light and inert gas -- neon. In fact, only by using a combination of in situ X-ray powder diffraction measurements, low temperature and high pressure have we been able to conclusively identify the neon atom positions beyond reasonable doubt."
Summarising the findings, Chris Cahill, Past President of the ACA and Professor of Chemistry, George Washington University said "This is a really elegant piece of in situ crystallography research and it is particularly pleasing to see the collaboration coming about through discussions at an annual ACA meeting."
Explosive oxygen burning [ edit ]
The oxygen-burning process can occur under hydrostatic and under explosive conditions. The products of explosive oxygen burning are similar to those in hydrostatic oxygen burning. However, stable oxygen burning is accompanied by a multitude of electron captures, while explosive oxygen burning is accompanied by a significantly greater presence of photodisintegration reactions. In the temperature range of (3–4)×10 9 K, photodisintegration and oxygen fusion occur with comparable reaction rates. Α]
Liar Liar, Pants on Fire: “Hot Bottom Burning” in Massive Stars
Stars are essentially element factories: most of the elements which we know (and dearly love, for life’s sake) were produced by some aspect of stellar evolution, either during their long, uneventful tenancy on the main sequence, shorter and swifter time as a red giant branch star, or their catastrophic death as supernovae (in a bit of timely astro-news, one of the closest supernova in recent times was discovered in the past few days, in the galaxy M51).
In this astrobite, we’ll first talk about stellar evolution and then present the paper after the second figure.
After spending most of their lives on the main sequence (where hydrogen burning occurs during the proton-proton chain or CNO cycle) of the Hertzsprung-Russell (HR) diagram (Figure 1), stars will move off the main sequence once a substantial fraction of hydrogen has been used up in the core of the star. Nucleosynthesis (and its accompanying heat-generation) ceases, causing the star to contract. As the star contracts, it heats up (due to the Virial theorem and hydrostatic equilibrium). With higher temperatures, hydrogen burning then resumes in a shell on the outside of the helium core, and the star moves quickly to the base of the red-giant branch of the HR diagram. Depending on the initial mass of the star, different processes could now take place (see Figure 2). If initial mass of the star is greater than 2.25 solar masses, the interior of the star will be hot enough for a smooth transition to helium burning via the triple-alpha process. This process and subsequent alpha particle captures will deposit carbon and oxygen in the core of the star. If the star is less than 8 solar masses, this core will cool, contract, heat up, and become increasingly electron degenerate. For the more massive stars in this range (6 to 8 solar masses), carbon burning can set in to produce magnesium (Mg), sodium (Na), and neon (Ne), resulting in an oxygen-neon-magnesium (ONeMg) white dwarf. Depending on the temperatures, this core can become degenerate.
Figure 1: The Hertzsprung-Russell Diagram, showing the evolutionary track of 2 solar mass star.(Figure from Herwig 2005)
This proto-white dwarf resides at the center of the star as shells of helium and hydrogen burn on top in an onion-shell structure. Thermal instabilities also occur and result in “thermal pulses” where runaway nucleosynthesis occurs on the surface of the degenerate cores. The ashes of these burning processes (He, C, N, O in the CNO equilibrium ratios) are left behind. If the initial stellar mass is less than 2.25 solar masses, the helium core will become degenerate before commencing triple-alpha burning. Once this degenerate core reaches 10^8 K, however, the triple-alpha process will start abruptly in a runaway reaction, because the degenerate material does not expand when heated like a normal layer of hydrogen. This is called the “helium flash,” where an intense amount of energy is deposited in a short amount of time. Incidentally, this same runaway thermonuclear burning but in a degenerate layer of hydrogen on the surface of a white dwarf is believed to be what powers novae. However, in this astrobite, we are concerned with stellar masses between 6 and 8 solar masses. For great introductory material on the physics of stellar evolution, check out the references at the bottom of this post.
Figure 2: Evolutionary chart showing what the end state of a star is based upon its inital mass.(Figue from Herwig, 2005).
“Dredge up” occurs during the transition between burning stages, when the core contracts (due to diminishing thermal support from the exhaustion of hydrogen, or later, helium) and the outer envelope of remaining material (such as hydrogen, or later, helium) expands (due to the hotter temperatures at its base). During this switch over, the convective outer envelope deepens its convection zone, and “dredges up” material from the inner core. This enrichment can be observed through spectroscopy of the surface layers of the star.
And so we reach the focus of today’s paper, hot bottom burning, which only occurs in massive (6-8 solar mass) asymptotic giant branch stars. When the convection zone in the outer layer of a massive star extends too deeply, it will pick up more material from the burning zone. Thus, the lower part of the convective zone is actually undergoing nuclear burning. The burning zone then has better access to fuel as it is imported via convection. A larger core mass means that hot bottom burning will be more efficient.
After reading this relatively brief description of stellar evolution, one may wonder, “how do we know this?” The answer is through many decades of observations and theoretical development including spectroscopy, astroseismology, solar flares, x-ray and radio observations, and detections of solar neutrinos. In their paper published on the archive, Ventura et al. examine the abundances of and correlations between magnesium, aluminum, and silicon in AGB and the more massive Super AGB (SAGB) stars. These elemental abundances are determined through spectroscopic observations of the visible surface of the star.
There are well-established anti-correlations between oxygen (O) and sodium (Na), and between magnesium (Mg) and aluminum (Al), meaning that more sodium is seen at the expense of oxygen. Mg to Al nucleosynthesis takes place in the helium shell, which burns via the triple alpha process. The synthesis of Al in SAGB stars is associated with the proton capture of Mg-24 in the deepest regions of the convective zone. This process is highly dependent on temperature, and in a narrow range of temperatures can switch from being the dominant process to the limiting reaction. SAGB stars can achieve these high temperatures necessary at the base of their convective zones, and thus convert much of the Mg into Al, driving the anti-correlation as Mg is depleted and Al is enriched.
Because the authors predict that the most extreme chemical compositions will derive from the AGB stars which are at the border of the AGB/SAGB limit (roughly 6 solar masses) they choose to exclusively model only these stars in their paper. The authors compare four different models with varying elemental compositions, and track their evolution over time. In addition to reproducing the magnesium-aluminum anticorrelation, the authors show that there is a positive aluminum-silicon correlation. Aluminum and silicon are believed to be positively correlated because a small part of the aluminum that is produced is converted into silicon (presumably the initial composition of silicon is small enough that the depletion of aluminum is not significant in exchange for a significant increase in silicon production).
Electron-eating neon causes star to collapse
Figure 1: An artist’s impression shows how an imaginary neon footballfish eats away at the electrons inside a star core. Credit: Kavli IPMU
An international team of researchers has found that neon inside a certain massive star can consume the electrons in the core, a process called electron capture, which causes the star to collapse into a neutron star and produce a supernova.
The researchers were interested in studying the final fate of stars within a mass range of eight to 10 solar masses, or eight to 10 times the mass of the sun. This mass range is important because it includes the boundary between whether a star has a large enough mass to undergo a supernova explosion to form a neutron star, or has a smaller mass to form a white dwarf star without becoming a supernova.
An eight- to 10-solar-mass star commonly forms a core composed of oxygen, magnesium and neon (figure 1). The core is rich in degenerate electrons, meaning there is an abundance of electrons in a dense space with high enough energy to sustain the core against gravity. Once the core density is high enough, the electrons are consumed by magnesium and then neon, which are also found inside the core. Past studies have confirmed that magnesium and neon can start eating away at the electrons once the mass of the core has grown close to Chandrasekhar's limiting mass, a process called electron capture, but there has been debate about whether electron capture can cause neutron star formation. A multi-institutional team of researchers studied the evolution of an 8.4-solar-mass star and ran computer simulations on it to find an answer.Figure 2: (a) A star core contains oxygen, neon, and magnesium. Once the core density becomes high enough, (b) magnesium and neon begin eating electrons and inducing a collapse. (c) Then oxygen burning is ignited and produces iron-group-nuclei and free-protons, which eat more and more electrons to promote further collapse of the core. (d) Finally, the collapsing core becomes a neutron star in the center, and the outer layer explodes to produce a supernova. Credit: Zha et al
Using newly updated data by Suzuki for density-dependent and temperature-dependent electron capture rates, they simulated the evolution of the star's core, which is supported by the pressure of degenerate electrons against the star's own gravity. As magnesium and mainly neon eat the electrons, the number of electrons decreased and the core rapidly shrunk (Figure 2).
The electron capture also released heat. When the central density of the core exceeded 10 10 g/cm 3 , oxygen in the core started to burn materials in the central region of the core, turning them into iron-group nuclei such as iron and nickel. The temperature became so hot that protons became free and escaped. Then the electrons became easier to capture by free protons and iron-group-nuclei, and the density was so high that the core collapsed without producing a thermonuclear explosion.
With the new electron capture rates, oxygen burning was found to take place slightly off-center. Nevertheless, the collapse formed a neutron star and caused a supernova explosion, showing that an electron-capture supernova can occur.Figure 3: The Crab Nebula, a remnant of the supernova in 1054 (SN 1054 observed by ancient astronomers in China, Japan and Arab). Nomoto et al. (1982) suggested that SN 1054 could be caused by electron capture supernova of a star with the initial mass of about nine times the sun. Credit: NASA, ESA, J. DePasquale (STScI), and R. Hurt (Caltech/IPAC)
A certain mass range of stars with eight to 10 solar masses would form white dwarfs composed of oxygen-magnesium-neon by envelope loss due to stellar wind mass loss. If the wind mass loss is small, on the other hand, the star undergoes the electron capture supernova, as found in their simulation.
The team suggests that the electron capture supernova could explain the properties of the supernova recorded in 1054 that formed the Crab Nebula, as proposed by Nomoto et al. in 1982 (Figure 3).
These results were published in The Astrophysical Journal on November 15, 2019.
- Electron degeneracy will not halt collapse (Chandrasekhar limit)
Gravitational compression heats core following each burning phase
At this point the star has an iron core, with shells of different elements burning at different temperatures
- Light nuclei (hydrogen, helium, carbon, oxygen, etc.) can fuse and release energy.
Heavy nuclei (uranium, plutonium, etc) can split (fission) and release energy.
Therefore, in a heavy star, we eventually build an IRON CORE and energy production of core ceases.
During the violent explosion the enormous expanding shock wave causes fusion to heavier nuclei.
- supernova energy emission
- Type I - binary system
- carbon-detonation supernova
- core-collapse supernova
- As the core of a massive star collapses,
- it will consist entirely of simple elementary particles
- electrons, protons, neutrons, and photons
- the structure of nuclei in the core has been destroyed
- Type I - binary system
- carbon-detonation supernova
- White dwarf grows from accretion of material from companion, eventually exceeding the Chandrasekhar mass limit
- core-collapse supernova
- Massive star expends its fuel supply, ending with iron core, and collapses and explodes
- During Supernova explosion, much (or most) of the star is ejected into space with a small fraction left behind.
- (for example, the Crab Nebula - M1
Crab Nebula and pulsar photographed by Hubble Space Telescope )
- (Example: 25 M SUN -> 24 M SUN ejected)
-or it all could be ejected
- If M<3M SUN , degenerate-neutron pressure will hold up weight of star.
- A pulsating radio source produced by rapidly rotating N-star.
1st pulsar discovered in 1968 by Jocelyn Bell, Cambridge U. (England) graduate student.
How Other Colors of Light Are Produced
You see lots of different colors of signs, so you might wonder how this works. There are two main ways of producing other colors of light besides the orange-red of neon. One way is to use another gas or a mixture of gases to produce colors. As mentioned earlier, each noble gas releases a characteristic color of light. For example, helium glows pink, krypton is green, and argon is blue. If the gases are mixed, intermediate colors can be produced.
The other way to produce colors is to coat the glass with a phosphor or other chemical that will glow a certain color when it is energized. Because of the range of coatings available, most modern lights no longer use neon, but are fluorescent lamps that rely on a mercury/argon discharge and a phosphor coating. If you see a clear light glowing in a color, it's a noble gas light.
Another way to change the color of the light, although it's not used in light fixtures, is to control the energy supplied to the light. While you usually see one color per element in a light, there are actually different energy levels available to excited electrons, which correspond to a spectrum of light that element can produce.
Watch the video: Reaktion zwischen Eisenwolle und Sauerstoff (December 2022).
- light curve of type I supernova matches theoretical calculations of light emitted by radioactive decay of nickel-56 and cobalt-56
- Many supernovae are discovered every year
- Latest Supernovae
- There are two types of supernovae
- The light curve reveals the two different types
- In Large Magellanic Cloud (see image of Magellanic Clouds)
160,000 light years from Earth
First Supernova visible to naked eye since invention of telescope
Exploding star was Sanduleak -69 o 202
Sanduleak -69 o 202 was 20 MSUN
Main sequence star for 10 7 years
- 10 46 watts (LSUN = 4 x 10 26 watts)
This exceeds the luminosity of all the stars in all the galaxies in the part of the universe we can observe, momentarily
- Then - in 1987- 20 hours before the supernova was visible, the pulse of neutrinos passed through the earth: 500,000,000,000,000 = 5 x 10 14 through every square meter .
- When companion expands in Red Giant phase, mass of White Dwarf increases and can exceed 1.4 M SUN .