Blog 3: Proton- Proton Fusion
This blog is all about what goes on in the nuclear furnace of a low mass star, such as our sun. First off, low mass stars primarily use proton- proton fusion to convert hydrogen into helium; this process is called “burning.” In general, proton–proton fusion can occur only if the temperature of the protons is high enough to overcome their mutual electrostatic or Coulomb repulsion. Coulomb’s law states that, “the force of attraction or repulsion between two point charges is directly proportional to the product of magnitude of each charge and indirectly proportional to the square of distance between them.” Simply put it explains the interaction between charged particles.
The theory that proton- proton reactions were the basic principle by which the Sun and other low mass stars burn was thought up by Arthur Stanley Eddington in early 1920s. When the theory came out, they found that the Sun’s temperature was too low to overcome the Coulomb barrier. After the development of quantum mechanics, it was discovered that tunneling of the wave functions of the protons through the repulsive barrier allows for fusion at a lower temperature than the classical prediction. Even so, it was still unclear how proton- proton fusion could still happen, because the product, helium-2, which is unstable and immediately dissociates back into a pair of protons. Hans Bethe proposed that the protons could beta decay into a neutron via the weak interaction during the brief moment of fusion, making deuterium the initial product in the chain. This idea was part of the body of work in stellar nucleosynthesis.
The figure on the left shows the proton- proton chain reaction. One question you might have is: why does it take four Hydrogen atoms to make one Helium atom? At first it seems like they have made a mistake here, the Helium atom has less mass then four Hydrogen atoms. Looking more closely at the diagram you can see that there is actually energy (gamma radiation) and positrons (anti- electron) that are released. This accounts for the missing mass and keeps it in the check with the law of conservation of matter.
Why is this important? I believe this will be a future energy of the world. One of the byproducts of the proton- proton chain reaction is Helium-3. Helium-3 is a very abundant extraterrestrial element that can be found on the moon and in earth. So it is not too far out there to say that if we can harvest this abundant element, then we can use it to master the power of nuclear fusion. The Chinese academy of Sciences has already stated on many occasions that one of the main goals of the program would be the mining of helium- 3. Byproduct of nuclear fusion would be the nice stable atom of helium-4, so there is no radioactive waste as with fission power. I think that this clean energy souse could help us stop our constant outpour of fossil fuel into our atmosphere. Maybe just maybe we will save the Earth’s climate before it’s past the turning point. As of right now though we are stuck with nuclear fission, but I believe (and am optimistic) that in the near future we will have the technology to contain fusion and use it to power the world.
Sources:
http://en.wikipedia.org/wiki/Proton%E2%80%93proton_chain_reaction
http://en.wikipedia.org/wiki/Coulomb_repulsion
http://en.wikipedia.org/wiki/Helium-3#Fusion_reactions
Ishfaq Ahmad, The Nucleus, 1:42,59, (1971), The Proton type-nuclear fission reaction
Kenneth S. Krane, Introductory Nuclear Physics , Wiley , 1987, p. 537.
Coulomb (1785a) "Premier mémoire sur l’électricité et le magnétisme," Histoire de l’Académie Royale des Sciences, pages 569-577
The theory that proton- proton reactions were the basic principle by which the Sun and other low mass stars burn was thought up by Arthur Stanley Eddington in early 1920s. When the theory came out, they found that the Sun’s temperature was too low to overcome the Coulomb barrier. After the development of quantum mechanics, it was discovered that tunneling of the wave functions of the protons through the repulsive barrier allows for fusion at a lower temperature than the classical prediction. Even so, it was still unclear how proton- proton fusion could still happen, because the product, helium-2, which is unstable and immediately dissociates back into a pair of protons. Hans Bethe proposed that the protons could beta decay into a neutron via the weak interaction during the brief moment of fusion, making deuterium the initial product in the chain. This idea was part of the body of work in stellar nucleosynthesis.
The figure on the left shows the proton- proton chain reaction. One question you might have is: why does it take four Hydrogen atoms to make one Helium atom? At first it seems like they have made a mistake here, the Helium atom has less mass then four Hydrogen atoms. Looking more closely at the diagram you can see that there is actually energy (gamma radiation) and positrons (anti- electron) that are released. This accounts for the missing mass and keeps it in the check with the law of conservation of matter.
Why is this important? I believe this will be a future energy of the world. One of the byproducts of the proton- proton chain reaction is Helium-3. Helium-3 is a very abundant extraterrestrial element that can be found on the moon and in earth. So it is not too far out there to say that if we can harvest this abundant element, then we can use it to master the power of nuclear fusion. The Chinese academy of Sciences has already stated on many occasions that one of the main goals of the program would be the mining of helium- 3. Byproduct of nuclear fusion would be the nice stable atom of helium-4, so there is no radioactive waste as with fission power. I think that this clean energy souse could help us stop our constant outpour of fossil fuel into our atmosphere. Maybe just maybe we will save the Earth’s climate before it’s past the turning point. As of right now though we are stuck with nuclear fission, but I believe (and am optimistic) that in the near future we will have the technology to contain fusion and use it to power the world.
Sources:
http://en.wikipedia.org/wiki/Proton%E2%80%93proton_chain_reaction
http://en.wikipedia.org/wiki/Coulomb_repulsion
http://en.wikipedia.org/wiki/Helium-3#Fusion_reactions
Ishfaq Ahmad, The Nucleus, 1:42,59, (1971), The Proton type-nuclear fission reaction
Kenneth S. Krane, Introductory Nuclear Physics , Wiley , 1987, p. 537.
Coulomb (1785a) "Premier mémoire sur l’électricité et le magnétisme," Histoire de l’Académie Royale des Sciences, pages 569-577
Blog 4: Mysterious Dark Matter
What is dark matter? It sounds like something that came out of an old science fiction novel. Dark matter, however, is firmly rooted in science fact. Dark matter is interesting because it is not like the everyday matter we are used to; it can’t be observed by telescopes, nor does it release or absorb any electromagnetic radiation. The only way that we can observe dark matter is by its gravitational effects on visible matter, light, and the structure of the universe. According to some estimates, dark matter accounts for over 84% of the matter of the universe.
One of the first people to find evidence and infer the presence of dark matter was a radio astronomer named Jan Oort, in 1932. That name should sound familiar because the Oort Cloud bears his name. Anyway Oort was studying the stellar motions in our local galactic neighborhood and found that the mass in the galactic plane must be more then the visible material could account for. In 1933, the astrophysicist Fritz Zwicky was studying clusters of galaxies, when he applied the virial theorem to the Coma cluster of galaxies and obtained evidence of unseen mass. He found that there was about 400 times more estimated mass than was visually observable.
The next logical question is what can be creating all this extra unseen mass? This leads us back to the present day where astronomers and physicists are still struggling with this question. There are two different possibilities of what dark matter could be: ordinary matter or extraordinary matter. The ordinary matter is usually referred to as MACHOs (Massive Compact Halo Object). Possible candidates for dark matter MACHOs are brown dwarfs, white dwarfs, and neutron stars/ black holes. WIMPs (Weakly Interacting Massive Particles) or the extraordinary matter consists of subatomic particles. WIMPs could possibly be: neutrinos, neutralinos (massive neutrinos), axions, photino, or a new subatomic particle. Some scientist estimate that ordinary matter might account for up to 20% of the dark matter. So what could the other 80% be?? I have read an article that said that the dark matter problem will most likely be solved within this decade. So within our lifetime we will unravel a secret that has puzzled scientists for almost a century.
The graph that I posted with this blog shows a galaxy’s rotation curve. This is one way that scientist have detected dark matter’s gravitational influence. One would expect (as is typical in our solar system) that the farther you get away from the gravitational center the slower you would move. That line is represented by ‘A’. However, what we actually observe when looking at a galaxy is something completely different, shown by line ‘B’. Our answer to this oddity is dark matter. We can also detect dark matter with gravitational lensing. Lensing relies on the effects of general relativity to predict masses without relying on dynamics, so it is a completely independent means of measuring dark matter.
Now why is this of any importance to you? As I said dark matter is said to account for about 84% of the total mass of the universe. That means that over 80% of the known universe we hardly know anything about. This is a big deal! We will never fully understand or universe if we can’t solve the dark matter problem. I personally am so glad that we live in a time where these mysteries that have plagued astronomers and cosmologist are beginning to be solved. I hope one day to help unravel one of these mysteries. For now I will stand on the sidelines and learn all I can.
Sources:
http://en.wikipedia.org/wiki/Dark_matter
http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/
http://science.howstuffworks.com/dictionary/astronomy-terms/dark-matter.htm
One of the first people to find evidence and infer the presence of dark matter was a radio astronomer named Jan Oort, in 1932. That name should sound familiar because the Oort Cloud bears his name. Anyway Oort was studying the stellar motions in our local galactic neighborhood and found that the mass in the galactic plane must be more then the visible material could account for. In 1933, the astrophysicist Fritz Zwicky was studying clusters of galaxies, when he applied the virial theorem to the Coma cluster of galaxies and obtained evidence of unseen mass. He found that there was about 400 times more estimated mass than was visually observable.
The next logical question is what can be creating all this extra unseen mass? This leads us back to the present day where astronomers and physicists are still struggling with this question. There are two different possibilities of what dark matter could be: ordinary matter or extraordinary matter. The ordinary matter is usually referred to as MACHOs (Massive Compact Halo Object). Possible candidates for dark matter MACHOs are brown dwarfs, white dwarfs, and neutron stars/ black holes. WIMPs (Weakly Interacting Massive Particles) or the extraordinary matter consists of subatomic particles. WIMPs could possibly be: neutrinos, neutralinos (massive neutrinos), axions, photino, or a new subatomic particle. Some scientist estimate that ordinary matter might account for up to 20% of the dark matter. So what could the other 80% be?? I have read an article that said that the dark matter problem will most likely be solved within this decade. So within our lifetime we will unravel a secret that has puzzled scientists for almost a century.
The graph that I posted with this blog shows a galaxy’s rotation curve. This is one way that scientist have detected dark matter’s gravitational influence. One would expect (as is typical in our solar system) that the farther you get away from the gravitational center the slower you would move. That line is represented by ‘A’. However, what we actually observe when looking at a galaxy is something completely different, shown by line ‘B’. Our answer to this oddity is dark matter. We can also detect dark matter with gravitational lensing. Lensing relies on the effects of general relativity to predict masses without relying on dynamics, so it is a completely independent means of measuring dark matter.
Now why is this of any importance to you? As I said dark matter is said to account for about 84% of the total mass of the universe. That means that over 80% of the known universe we hardly know anything about. This is a big deal! We will never fully understand or universe if we can’t solve the dark matter problem. I personally am so glad that we live in a time where these mysteries that have plagued astronomers and cosmologist are beginning to be solved. I hope one day to help unravel one of these mysteries. For now I will stand on the sidelines and learn all I can.
Sources:
http://en.wikipedia.org/wiki/Dark_matter
http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/
http://science.howstuffworks.com/dictionary/astronomy-terms/dark-matter.htm