A new theory suggests that a "wind" of ionized particles from a star may have spurred a change in the distribution of mass inside of our sun's nebula, causing some hydrogen to clump together and form our sun. The solar wind is something that is very familiar to our part of the solar system. It is a contiuation of the sun's corona which extends all the way past Pluto to the heliopause, where it meets the interstellar wind, which finally ends any significant effects of the solar wind. It is composed of a plasma. A plasma is a gaseous state consisting of positive and negative ions and which is very liable to electrical and magnetic interactions because of its possibilities for conductivity.
When the sun was a T-Tauri star (a baby which didn't fuse Hydrogen yet) it emitted 1000 times more solar wind than it does now, and even now it is still emitting enough to help cause auroras, geomagnetic storms, communication problems on satelites and, every once in a while a really really energetic particle like the "Oh My God" particle, which was a proton with as much energy as a 60 mpH baseball!
It was thought that the sun formed from its nebula because of a shockwave from a nearby supernova which changed the density of the nebula and allowed some the of the hydrogen to clump together. Now, though, scientists are proposing a less explosive culprit, stellar wind.
Monday, June 04, 2007
Saturday, June 02, 2007
Axions: Fact or Fiction?
Axions are theoretical particles that, if verified, could help explain what dark matter is made of.
Why do we need Axions?
In 1977, Roberto Peccei and Helen Quinn proposed an elegant solution to the strong CP problem which required a new particle, which they called an axion. It's named after a popular detergent of the time because they had "cleaned up" the problem.
CP Problem? What are you talking about?
CP stands for charge conjugation(C) and parity(P). They are symmetries in Particle Physics. In other words, we somehow change the conditions of an experiment in order to check whether a certain symmetry can be maintained under some circumstances. Charge conjugation is a symmetry involving particle/anti-particle trasitions. Think of parity as a reflection symmetry. When put together they make CP symmetry. It was established in the 50's that Parity violation (reflection) was broken in weak nuclear interactions. This was exciting as this symmetry wasn't broken in any of the other forces. So Physicists combined Parity with Charge Conjugation and thought that together they wouldn't be broken. Wrong. Even together weak interactions still violated the symmetry. So CP Violation was discovered in the weak force.
What about the Strong CP Problem?
Well, when the experimentation was carried over to the strong nuclear force, Physicists were puzzled that CP symmetry did not appear to be violated much, if at all. One parameter in the theory of Quantum Chromodynamics [QCD] (the theory of the strong force) had to adjusted very precisely in order to agree with experimental data. The Strong CP problem is basically asking why the Strong Force doesn't suffer from CP Violation like the Weak force does.
What about Axions?
Like I was saying there is a very precise parameter in QCD which is very close to zero but not quite there in order to compensate for the lack of CP Violation. Peccei and Quinn suggested the elegant idea of making this parameter into a new field, and where there is a field there must be a new particle of that field. In this case this particle would be called an axion. This may sound contrived but it is legal. Peccei and Quinn suggested a new symmetry (Peccei-Quinn symmetry) that would be spontaneously broken and produce this new particle, allowing the parameter from QCD to drop to zero, which seems more natural.
How do we detect Axions?
It is theorized that Photons, when exposed the magnetic fields, will spontaneously change into Axions. One novel way to detect them that has come up this week was discussed in depth here. Basically, we will wait until a giant quasar goes behind our sun and then we will wait to see whether we will still be able to detect anything from the quasar even though the sun is in the way. The idea is that high energy photons from the quasar will change into axions from the suns magnetic field and then change back and come to us.
So what if we find them?
If we find them then we may have an answer to what dark matter is. They are theorized to be very light (maybe less an meV) but they are also theorized to have been created in huge numbers during the big bang, when they would have lost all of their kinetic energy and become Bose-Einstein Condensates (substances that can't lose any more energy and can't degenerate into anything smaller).
Why do we need Axions?
In 1977, Roberto Peccei and Helen Quinn proposed an elegant solution to the strong CP problem which required a new particle, which they called an axion. It's named after a popular detergent of the time because they had "cleaned up" the problem.
CP Problem? What are you talking about?
CP stands for charge conjugation(C) and parity(P). They are symmetries in Particle Physics. In other words, we somehow change the conditions of an experiment in order to check whether a certain symmetry can be maintained under some circumstances. Charge conjugation is a symmetry involving particle/anti-particle trasitions. Think of parity as a reflection symmetry. When put together they make CP symmetry. It was established in the 50's that Parity violation (reflection) was broken in weak nuclear interactions. This was exciting as this symmetry wasn't broken in any of the other forces. So Physicists combined Parity with Charge Conjugation and thought that together they wouldn't be broken. Wrong. Even together weak interactions still violated the symmetry. So CP Violation was discovered in the weak force.
What about the Strong CP Problem?
Well, when the experimentation was carried over to the strong nuclear force, Physicists were puzzled that CP symmetry did not appear to be violated much, if at all. One parameter in the theory of Quantum Chromodynamics [QCD] (the theory of the strong force) had to adjusted very precisely in order to agree with experimental data. The Strong CP problem is basically asking why the Strong Force doesn't suffer from CP Violation like the Weak force does.
What about Axions?
Like I was saying there is a very precise parameter in QCD which is very close to zero but not quite there in order to compensate for the lack of CP Violation. Peccei and Quinn suggested the elegant idea of making this parameter into a new field, and where there is a field there must be a new particle of that field. In this case this particle would be called an axion. This may sound contrived but it is legal. Peccei and Quinn suggested a new symmetry (Peccei-Quinn symmetry) that would be spontaneously broken and produce this new particle, allowing the parameter from QCD to drop to zero, which seems more natural.
How do we detect Axions?
It is theorized that Photons, when exposed the magnetic fields, will spontaneously change into Axions. One novel way to detect them that has come up this week was discussed in depth here. Basically, we will wait until a giant quasar goes behind our sun and then we will wait to see whether we will still be able to detect anything from the quasar even though the sun is in the way. The idea is that high energy photons from the quasar will change into axions from the suns magnetic field and then change back and come to us.
So what if we find them?
If we find them then we may have an answer to what dark matter is. They are theorized to be very light (maybe less an meV) but they are also theorized to have been created in huge numbers during the big bang, when they would have lost all of their kinetic energy and become Bose-Einstein Condensates (substances that can't lose any more energy and can't degenerate into anything smaller).
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