Recent Solar Storm

Since my last blog was about the magnetic fields of the planets, I think it would be good to talk quickly about the recent protection this field gave us. At the beginning of March the sun had one of its more violent solar storms, expelling vast amounts of particles throughout the solar system. If it weren't for our magnetic field we could have been in very bad shape after the particles went by us. See our magnetic field acts sort of similar to the force fields around space ship that you would see in sic-fi movies, when it comes to these particles. If it wasn't for this fact there could be disastrous effects on our everyday life. For example our electrical infrastructure could be toppled, due to the particles causing the systems to short circuit and such.

Here is a picture of Earth's special "force field"

Now the beauty that comes along with the terror, this is the aurora that was caused by the storm

Magnetic Fields(INDUCTION!!!), Who Have Them and Who Don't?

The Earth as we all know has a very active magnetic field. As it turns out it is not just our planet that produces a magnetic filed. In fact nearly all of the planets in our solar system produce some sort of magnetic field themselves. Before looking at the other planets lets take a moment to understand our own magnetic field. So first we need to know what actually makes a magnetic field. Magnetic fields are most usually the resultant of the motion of some charged particle, and that is exactly what is occurring with Earth. The Earth's core is composed of two parts the inner core and outer core. The inner core is a solid composite of iron and nickel, while the outer core is also iron and nickel, however simply liquid. What happens is the liquid core swishes about the solid core the electrons in the outer core move about creating what we know as our magnetic field. So in our case it was pretty easy to see why we have a magnetic field, What about the other planets? As it turns out most of the planets generate magnetic fields in a very similar way as the Earth does. But wait!, if the reason for our magnetic field is the molten metal in our core what about the jovian planet? These planets definitely do not have molten cores to generate their fields.

Real quick here is a list of planets and their magnetic fields relative to Earth's:

Mercury 100*Earth Field

Venus (1/25000)*Earth field

Earth ~50µT

Mars (1/5000)*Earth Field

Jupiter 20000*Earth Field

Saturn 540*Earth Field

Uranus 40*Earth Field

Neptune 0.25*Earth Field

Pluto None measurable

Sun Variable

First lets look at the rocky planets. In fact all of the rocky planets do have measurable magnetic fields, however the range all over the place in reference to Earth's magnetic field. Although it is not known for sure the cause of each of the fields, it is hypothesized that many are made in similar ways to Earth's. However notice the two strange values above the fields of mars and venus, they have rather small fields compared to the Earth. Mars does not have a molten core as Earth, but little is known as to what produces its field. Venus as you can see above has a very small field as compared to the Earth. Venus also does not have a liquid core and however it also rotates at a very slow speed, these are thought to be the main reasons for its tiny field.
Then there is the no longer terrestrial planet pluto, which has no measure of ever having a magnetic field.
Now how about the gas planets they rotate nicely, but they do not have a molten core as a source of moving charge for their fields. These planets actually have something very similar going on, instead of molten metal they have liquid metallic hydrogen causing their fields, which looking at jupiter has quite good potential for field production as molten cores do. Notice as we go further form the sun these fields drastically drop in magnitude, this is because as we go further the system gets cooler, and there is less liquid metal to generate fields.
Also I should mention the Sun. From the 3table I provide above you could see that the sun's field is not defined. This is because it undergoes something called differential rotation, meaning that material at the center of the sun rotates faster at the center and slower at the poles. this causes crazy magnetic fields that change all the time. Also as you may have guessed the the Suns produces its field similarly to the Earth, motion of charged particles.

Picture of our magnetic field deflecting charged particles from the sun.

Shooting Stars

So buy know we should realize that What most people refer to as shooting stars are actually comets. So it may shock you to realize that there is something very similar to a shooting star that exists. When we think of a star it is good to think of it as revolving about the galaxies core as we do about our own sun. So it would be strange to think that a star could be shooting
off like a comet. However, just as planets, there do exist stars that can break away from their orbit in the galaxy. So, how do these come to be. There are two main resins for a star to be ejected from its orbit. One method would be for a supernova explosion to give off enough energy to knock the star out of orbit. The other way would be for two binary systems to interact and causing star(s) to be ejected from its orbit. These stars when ejected are given some extra energy, meaning that they are given some more velocity when they are ejected. In fact there are two sort of classes of these stars. First there are the high velocity stars which are observed to be moving at a speed of the order of 100 km/s.
Then there are what are know as the hypervelocity stars, these are the true shooting stars. Hypervelocity stars move with speed on the order of 1000 km/s. These stars however are quite rare. These stars are thought to originate in a way similar to the other high velocity stars(binary interactions), however, they are a little more interesting. rather than having two interacting binary systems causing the break, it is though that it is the systems interaction with a blackhole. When the binary system gets close to the black hole one of the stars are grabbed by the blackhole, while the other is ejected with a boost of extra velocity. All known hypervelocity stars are main sequence stars and smaller in mass than our sun. These things are so rare that there are only 16 known hypervelocity stars and only 1000 out of the 100 billion stars in the milky way are thought to be hypervelocity stars.


Above is an animation of how these stars are given their velocities. Notice the binary system com in in from the upper right. It will come close to the black hole at the center of the galaxy and undergo the process as described above.

An artists depiction of a hypervelocity star.

The Big Bang and the Epoch's of Creation

The Following is a list and small description of what was going on during the few fractions of a second after the big bang. Time frames are given in what are known as epochs, being that in a certain tome frame something significant is occuring.
1)The Planck Epoch
-ocurring 10^-43 seconds after the big bang
-Fundamental forces unifed as a single force
-extremely high temperature
2)Grand Unification Epoch
-occured between 10^-43 and 10^-36 seconds after the big bang
-gravitational force breaks away from the other forces(known as the gauge forces)
-cooling begins due to expansion
3)Inflation Epoch
-occured between 10^-36 and ??? seconds after the big bang
-inflation similar to the inflation due to dark matter occurs
-some theorize that the expansion may have something to do with the higgs boson.
-the end of this epoch is unknown, in fact some believe that it may be infinite in time.
4)Electroweak Epoch
-occured between 10^-36 and 10^-12 seconds after the bbig bang
-more cooling
-the strong and weak forces are able to break from each other due to the cooling
5)Baryogenisis
-this is the time that the constituens of the particles we know best are created.
-baryons are the familiar protons, neutrons, electrons
-this is when we noticed a deviation in the distribution of matter, in other words non-equal parts of matter and anti-matter.
-unable to form yet, just begin process of formation
6)Super-Symmetry Breaking
- after Baryogenisis
-theorized that each particle much have a super-symmetric partner, for each fermion there should exist a partner boson.
-this however is not seen, it is believed that the universe did obey this law up until this point
7)Quark Epoch
-between 10^-12 and 10^-6 seconds post the big bang
-particles achieve their mass during this epoch
8)Hadron Epoch
-between 10^-6 and 1 second after the big bang
-cooling
-finally the hadrons (protons, neutrons, etc) are able to from.
9)Lepton Epoch
-between 1 and 10 seconds after the big bang
-annihalation between particle and antiparticle occurs
-cooling
-called lepton epoch because leptons are the prevailing particles in the universe post annihaliation.
10)Nucleo-Synthesis
-occuring 3 minutes after the big bang
-universe is now cool enough for particles to fuse and create the nuclei of atoms.

Binary System Mass Transfer

When stars are part of a binary system it is possible for the two to sometimes transfer stellar mass between each other. This occurs when one of the two stars grows too large. It is similar to an equilibrium maintaining system. In order to maintain steady states for each star there will occur a transfer of mass from one to the other. This effect has in fact been quite well measured. For example it is know the limit to which the star can grow without departing some of its mass on its companion star. The limit is known as the Roche Lobe. The Roche Lobe is the minimum distance from the star wherein mass remains gravitationally bound to the star. When the star reaches this limit it begins its transfer. In fact the point which this transfer occurs is at the first Lagrangian point.

Above is a depiction of mass transfer where the donor star creates an accretion disk around the other star. This is a typical method of mass transfer, however not the only. At times rather than creating an accretion disk, mass can be delivered directly on to the recipient star. Another outcome would be for the donning star to release its mass elsewhere such as solar winds.

Below I have two equations are the equations for the Roche Lobe radius of Mass 1 of a binary system. Note the dependence of these equations on the masses of the two stars and their ratio.

Gamma Ray Bursts

     So, in class we sort of ended on the subject of the death of stars. I was particularly interested in the outcome of the most massive stars. Particularly the creation of black holes. When I began researching them I noticed something very interesting that they produce in the process of their formation, gamma ray bursts.  A gamma ray burst is a jet of high energy photons that are expelled by a star during its collapse. These bursts are relatively short but they are immensely luminous. These things are said to be able to light up the whole universe. They are also quite frequent, earth orbiting satellites pick up these bursts on average about one per day.

     These bursts occur during the supernova explosion death of a star.  The rays burst out at opposite angles from the supernova explosion. The time frame of the bursts  can last anywhere from milliseconds to a few minutes, however they are generally on the scale of a a couple of seconds. After this initial burst the former star continues to emit radiation in lower energy wavelengths, known was the afterglow.  These are particularly interesting because of the amount of energy they produce, in just the few seconds that they are active will emit as much energy as our sun in its entire lifetime. Another interesting note about gamma ray bursts is that they are thought not to only be the by-product of super nova but also things such as the merging binary stars in a system, or a magnetar(special type of neutron star).

The video above is a clip from the discovery channel showing the death of a star and the production of gamma ray bursts.

Photon propulsion

     As space travel becomes more and more expensive, we will need more frugal methods of transport. One proposed method would be the use of somewhat new technology, solar sails. Solar sails are extremely thin sheets of metal that work similar to regular naval sails. Naval sails use the pressure built up behind them as a means of propulsion of their vessel, solar sails analogously use pressure built up behind them as well to propel their payloads.  However the pressure used by these sails come from soar wind and radiation pressure. As we know even though the photon is a massless particle it still has a momentum attached to it, this momentum can be harnessed by these sails as a means of propulsion.

     One character very important characteristic about these sails is that they must be very large in area. This is to obtain a sizable amount of pressure built up to gain some propulsion. A draw back of of these sails is that like many of the physical forces, the force that propels these sails falls of as one over the distance squared. Also the forces themselves are quite weak to begin with. For example force given by the radiation pressure goes as 10^-6N/m^2, and solar wind goes as 10^-9N/m^2(these are as seen from the distance of the earth and given by our sun). This drawback may not be as bad as it seems, because devoid of other forces in space the sail may be able to maintain a long voyage with no cost of rocket fuel. Also when these are in use the sails are limited in their pointing because the maximal force is given when the sail is perpendicular to the sun's rays. This could greatly hinder navigation other than  straight away from the source.

Attack of the Clones solar sail use

IKAROS solar sail, artist rendering

     Although this is a somewhat new technology, it has been seen in the media for a while and has been used in sic-fi movies quite realistically. Above is a picture of a solar sail being used in Star Wars: The Attack of the Clones in 2002. This is because until recently people did not believe that these would work. However, in 2010 the Japan Aerospace Exploration Agency (JAXA),  actually launched their sail and measured solar propulsion acting on it.  Now the next step is making them more efficient. This means the engineering of thinner sails, more reflective sails (because propulsion is better transferred through reflection than absorption of light) and a more sturdy design. This has actually already begun with the creation of sails that spin, which use angular momentum to make the sails retain their shape.

Actual IKAROS sail

Above is a small clip from the movie where you can see the sail being used.
Radiation pressure, given as the time averaged intensity of light divided by the speed of light squared.
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