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The most important reactions in stellar nucleosynthesis:
- Hydrogen fusing:
- Helium burning:
- Burning of heavier elements:
- Lithium burning: a process found most commonly in brown dwarfs
- Carbon-burning process
- Neon-burning process
- Oxygen-burning process
- Silicon-burning process
- Production of elements heavier than iron:
- Neutron capture:
- Proton capture:
- The Rp-process
- Photo-disintegration:
- The P-process
Green Tremblay
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Why is iron the heaviest element that can be produced by star?
It isn't; heavier elements can be, and are, produced by DYING stars. The reason is the "packing fraction curve". As atomic nuclei would fuse together within the cores of normal stars, hydrogen atoms as "fuel" would fuse into helium "ash"; when the star became old, the core of the stars would heat up and become more dense as the star began to collapse into itself. The denser stellar core material would heat up and begin to fuse into heavier elements; carbon, oxygen, and heavier elements, releasing a little energy every time a new atom was formed by fusing together lighter ones - UNTIL they got to iron. Once you get to iron, any additional fusion sucks energy OUT of the star's core, and every fusion from there on sucks even MORE energy out of the star, leading to the star's quick collapse. This is one scenario for how a "nova" might occur. If a star EXPLODES in a supernova, then there's LOTS of energy to crash even heavy elements together into even HEAVIER elements. So all of the gold, uranium, lead, and every atom heavier than iron, was formed in a supernova explosion.
What is the source of all elements in the universe that are more massive than iron?
The primary sources of these elements are fusion reactions in stars (the plural is there because there are hundreds, if not thousands, of different reactions that take place in stars).The reason that iron is significant is that two of its isotopes (56Fe and 58Fe) are the around the most stable nuclei of any element (56Fe is often wrongly attributed to be the most stable nuclide, but that distinction actually goes to 62Ni - 56Fe comes in third after 62Ni and 58Fe).As a result, fusion reactions (nuclear reactions that combine smaller elements to make larger ones) that take place to give progressively heavier elements up to nickel (just beyond iron in the periodic table) will give out energy. To form elements larger than iron, energy has to be put in to the reaction. It is the fusion reactions that give elements up to nickel, which give out the energy from stars.The consequence of this is that any elements heavier than nickel which may be temporarily formed in a star will undergo fission reactions that give smaller elements. Elements heavier than iron are generally formed in supernovae, where a star coming to the end of its life (and therefore containing plenty of heavy elements) produces a massive energy output that fuels the formation of heavy elements and scatters them to interstellar space before significant losses due to fission can take place.
If a star runs out of fuel when all of the elements inside it are fused to iron how are the heavier elements created?
During the main life cycle of a star, no elements heavier than iron can be created, and that's only in very massive stars (our sun is only massive enough to fuse hydrogen into helium). Your question is a very good one, and if you thought of it on your own, you should be proud. Every element heavier than iron is created when the star dies. Specifically, when it becomes a super-nova. When all the lighter elements have been fused, the star can't generate enough energy to resist its own gravity, so it collapses in on itself. The result is a sudden gigantic spike in pressure that creates all the heavier elements. As if it weren't cool enough that we're all made from star-stuff, a good bit of us is made from supernovae, too!
Why a stars collapses when iron is the only element left in the core?
When hydrogen fuses into helium, extra energy is released, causing more fusion. When helium fuses into carbon, extra energy is released, causing the reaction to continue. When each element fuses into heavier ones, energy is released - until you get to iron.When iron fuses into heavier elements, or when anything fuses into elements heavier than iron, it sucks energy OUT of the reaction, slowing it down. This is like poison to a nuclear reaction; sucking the energy OUT of a star rather than releasing it. The star dies instantly, and the collapse causes a titanic explosion in which even MORE energy is sucked out of the core of the star, as heavy elements fuse into heavier ones, until the heavy elements like Uranium and thorium are so massive that they cannot hold together and begin to fall apart._____________________________________________________________________The above answer isn't exactly right. An over simplification.Normal stars, like our sun, live just long enough to begin fusing helium into carbon. At that stage, they generate so much energy that they essentially boil off their outer layers, in a stellar nova. Eventually they boil off everything but their inner carbon core, leaving a white dwarf. But giant stars, like Betelgeuse, have enough mass to hold together. This mass, and the immense force at the stars core, provides enough energy to fuse carbon into heavier elements.Nuclear fusion is not easy. So far we have only achieved it through a two step reaction, beginning with a nuclear fission explosion. You have to put energy in to get energy out. The reason is the electromagnetic charge of the atomic nucleus. The nucleus is made of positively charged protons and neutrally charged neutrons. It takes a lot of force to overcome these charges. The bigger the nucleus, the more force required to fuse it.So, after fusing all of its available helium into carbon, the star is on borrowed time. Each stage in the star's fusion cycle is shorter than the last, simply due to the availability of the fuel. After billions of years of fusing hydrogen, millions of fusing helium, time quickly runs short. Carbon fusion last about 600-1000 years. Carbon fusion produces neon, neon fusion lasts roughly 1 year. Next is oxygen fusion, lasting maybe 6 months, producing silicon. But then, something strange happens. In every previous step of the fusion cycle, fusion produces more energy than it consumes, but iron is the other way around. Silicon fusion produces iron, but iron fusion requires too much energy, effective ending all nuclear fusion at the core. Silicon fusion lasts 3-5 days, and at that time there is not enough energy left in the core to fuse anything, and the core collapses under the weight of the stars mass. This collapse goes until protons an neutrons are crushed together so tight the the entire mass becomes pure neutrons. This stops the collapse momentarily, sending enormous shock waves through the stars outer layers, causing massive runaway nuclear reactions, blasting the star apart in a type II super nova. The runaway nuclear reactions produce elements heavier than iron through neutron accumulation. At the core, one of two things happens: Either the nuclear forces stop the collapse, forming a neutron star, or the force of the collapse overpowers the nuclear forces, and the core collapses into a black hole.On a related note, the star Betelgeuse, mentioned earlier, is a red super giant, and is believed to be rapidly supernova. In fact, given its distance of over 800 light years away, it is likely that it already has gone supernova. When it does, or rather when the supernova's light reaches earth, it will outshine even the full moon in the night sky, and be easily visible in broad daylight. The supernova will last about 6 mouths, before fading away for good. It should produce a neutron star.______________________________________The above statement "Nuclear fusion is not easy. So far we have only achieved it through a two step reaction, beginning with a nuclear fission explosion." is not completely true, referring to the "so fare we have only" part. We have achieved cold fusion by using super conducting magnets to drive hydrogen particles into each other. They reach speeds near light speed, then clash into each other. If the collision is direct enough they will fuse into helium. This produces far more energy than the energy used to crash them into each other. Once we find a way to harvest that energy we can create cold fusion reactors.________________________________________Well, just a small addition. Fusion has been accomplished with lasers also. Work at the National Ignition Facility Lawrence Livermore Laboratories, has produced small fusion reactions and they hope to create a sustained reaction at some point.
What is the mass of the lowest-mass stars?
From Wikipedia: "For stars with similar metallicity to the Sun, the theoretical minimum mass the star can have, and still undergo fusion at the core, is estimated to be about 75 times the mass of Jupiter. When the metallicity is very low, however, a recent study of the faintest stars found that the minimum star size seems to be about 8.3% of the solar mass, or about 87 times the mass of Jupiter. Smaller bodies are called brown dwarfs, which occupy a poorly defined grey area between stars and gas giants." Comment 1: Metallicity refers to the percentage of elements heavier than helium (not "metals" in the chemical sense). Comment 2: Basically, a brown dwarf gets hot enough to fuse deuterium (hydrogen-2), but not regular hydrogen (hydrogen-1), which severely limits the amount of energy it can produce.
What are some characteristics of stars that might account for the fact that some have more complex elements in their spectra?
Older age might account for it. As a star ages, it uses up the simplest elements (hydrogen . . . helium . . .) then starts fusing heavier and heavier elements. Our Sun will get to the point of fusing iron, which is pretty heavy, but the truly large stars out there will fuse elements much heavier than Iron. These heavier and heavier elements may account for some stars having more complex elements in their spectra.
What does nucleur fusion create inside stars?
First hydrogen nuclei fuse to form helium, and then as the star ages heavier and heavier elements are formed.
What fuel is used by red giant stars?
After using up its hydrogen-1, the star becomes a red giant. It will start fusing helium-4 into heavier elements. It may also fuse heavier elements, to get other elements that are yet heavier.
How are the elements carbon nitrogen and oxygen produced in stars like the sun?
These fusion (carbon , nitrogen , and oxygen) reactions form nuclei of sightly heavier elements.
What element does a star run out of that causes them to die?
Hydrogen and helium; those two elements are the fuel for the stars. First they fuse hydrogen to helium, later they fuse helium to heavier elements.
The death of a star occurs when?
When the star runs out of fuel. Most stars burn (fuse, actually) hydrogen. When this runs out, what happens next depends on the mass of the star... heavier stars can fuse heavier elements for a short time, but lower mass stars simply collapse into white dwarfs.
What do Hydrogen bombs and stars both produce energy with nuclear?
The term is nuclear fusion, where light elements (usually hydrogen) fuse to form heavier elements.
How elements are formed in stars?
By nuclear fusion and neutron captureRight now the sun is fusing hydrogen into helium.Later in its life it will fuse helium into carbon.All elements are made inside stars. Massive stars are more efficient than low mass stars at making elements heavier than carbon.
Define the stellar theory?
If your referring to Stellar Nucleosynthesis, then its when stars fuse the smaller elements (Hydrogen,Helium) to make the heavier elements (iron, gold, silver,zinc, etc).
Are elements formed by years of compression under the earths crust?
No.All elements (since the creation of the Universe) are formed by either combining two lighter elements in to a heavier one (called nuclear fusion) or by splitting a heavy element into 2 (or more) lighter ones (called nuclear fission).It is believed that at the creation of the Universe mostly hydrogen (and some helium) was present. Hydrogen is by far the most common element. These are the two lightest elements. Inside stars these elements are fused together to form heavier elements. Our very own Sun, for example, fuses hydrogen atoms together to form helium. This process releases energy in the form of heat and light.A star is able to do this due to the tremendous heat and pressure within it. There are different types of stars, and some have even more staggeringly high pressures inside them allowing them to fuse together and form heavier elements than helium. It is believed that when a star dies, and goes supernova, the tremendous force at this point can fuse and create even heavier elements still. This explains why the heaviest elements are the rarest elements.So, we have stars to thank for all the elements that exist. The pressures and temperatures within the Earth are just not high enough to fuse atoms together.
Why can't a star fuse chemical elements beyond iron?
It sure can - and some stars do, to a minor degree. However, it can no longer gain energy from this fusion - it costs energy to create heavier elements. --- To fuse Iron, you would need a huge amount of heat and pressure, higher than what can be provided by even the massive stars is existence. The upper limit of a stars mass puts this limit on what materials it can fuse. Elements heavier than Iron are created during a supernova explosion, the death of a massive star.
How big do stars have to be in order to be able to fuse together elements heavier than iron?
According to the Book on Astronomy written by Susan Douglas and Ryan Smith, they must be anything taller than a minimun of 1,200 m (meters)
