Strong magnetic fields aided formation of solar system

[dougettinger]

Neufer made a very interesting statement during our discussion of why spins and orbits are in the same direction. Allow me to quote Art: "When the solar system was formed it was probably a plasma locked into a constant rotation rate by strong magnetic fields. You cannot ignore the plasma/magnetic field aspects and expect to get the right answers."

I am not disputing this statement. But I desire more details. A cold molecular cloud of dust and gases starts to collapse due to some higher concentrated density gradient. How is the plasma and magnetic field generated ? Certainly a magnetic field can be generated if ions and electrons in a plasma are in motion, but what energy caused the plasma which needs very high temperatures to exist ? How does the plasma become "locked" into a constant rate ? And why is this constant rotation rate required to get the right answers ? This is just a friendly discussion; please don't allow Chris to intimidate you.

Neufer also suggested that the solution lies in the fact that almost all of the angular momentum of solar system lies in the planets themselves. Art, if you have some new idea about why this helps the solution, could you share it. By the way, most of the angular momentum of the solar system is in the orbital velocites and not the rotation spin of the planets. This is indeed for me a big part of the solution.

Art, I am definitely in agreement with you saying that to get the right answers or solution you need magnetism. But which magicians hat did you pull the magnet from ? Maybe I can supply the magic wand for you.

My new friend, Thoth, explained that magnetic fields were strong interior to 1 AU and past 100 AU. I imagine that as the protostar begins to gain energy, it transfers radient energy to the extreme inner part of the disk thereby creating plasma and magnetic effects. How are plasma and/or magnetic effects created at the extreme, cold perimeters of the protosar disk ?

Doug Ettinger, Pittsburgh, PA 3/20/2011

[Chris Peterson]

A cold molecular cloud of dust and gases starts to collapse due to some higher concentrated density gradient. How is the plasma and magnetic field generated? Certainly a magnetic field can be generated if ions and electrons in a plasma are in motion, but what energy caused the plasma which needs very high temperatures to exist ?

The source of energy is gravity. The basic underlying concept of all models describing stellar system formation has gas (and a little dust) condensing because of self-gravitation, and as it condenses, it heats. That's what plasma is: hot gas. Where magnetic fields are likely to be significant is in the protostar itself. It will ionize some of the more tenuous outer gas, but I personally doubt that magnetic fields play much role in planetary formation. That was all going on in a much cooler regime, where there was no medium for significant currents to flow, and therefore no mechanism to support a large magnetic field. Magnetic fields in the protostar, of course, like in the mature Sun, may well play an important role in how the star develops. Or not. I don't think there is any sort of consensus on that issue. Of course, the trickiest bit of the system to model is the protostar and circumstellar accretion disc, right near the transition between a dense disc and a collection of isolated planetesimals. That is analogous to a phase change- always problematic to model accurately. That would seem to represent the best opportunity for magnetic effects to translate to structure.

[dougettinger]

Hello Chris,

I have missed your companionship. I have been away for about two weeks. I do agree with all that you stated. This issue is about how the planets obtain the same angular momentum vector for both their orbits and spins. And, I agree with you that there is no reason to have high enough temperatures to create plasma and magnetic properties at the planetary distances from the protostar Sun. But the Neufer made an interesting statement which should not be entirely dismissed. To get the solution for all the angular momentum vectors being aligned you need electromagnetic properties. Let's ponder that statement; maybe a light bulb will come on.

Doug Ettinger, Pittsburgh, PA 3/20/2011

[dougettinger]

A cold molecular cloud of dust and gases starts to collapse due to some higher concentrated density gradient. How is the plasma and magnetic field generated? Certainly a magnetic field can be generated if ions and electrons in a plasma are in motion, but what energy caused the plasma which needs very high temperatures to exist ?

The source of energy is gravity. The basic underlying concept of all models describing stellar system formation has gas (and a little dust) condensing because of self-gravitation, and as it condenses, it heats. That's what plasma is: hot gas. Where magnetic fields are likely to be significant is in the protostar itself. It will ionize some of the more tenuous outer gas, but I personally doubt that magnetic fields play much role in planetary formation. That was all going on in a much cooler regime, where there was no medium for significant currents to flow, and therefore no mechanism to support a large magnetic field. Magnetic fields in the protostar, of course, like in the mature Sun, may well play an important role in how the star develops. Or not. I don't think there is any sort of consensus on that issue. Of course, the trickiest bit of the system to model is the protostar and circumstellar accretion disc, right near the transition between a dense disc and a collection of isolated planetesimals. That is analogous to a phase change- always problematic to model accurately. That would seem to represent the best opportunity for magnetic effects to translate to structure.

I am quoting from Steven Balbus' "Magnetohydrodynamics of Protostellar Disks". "The MRI (magnetorotational instability) depends upon the presence of electrical currents to do its job, and this means that the disk gas must be at least partially ionized. "Partially ionized" in practice could mean even a minute electron fraction. Tiny traces of electrons can magnetize the disk, an effect we will quantify in Section 8. It is because dynamical significance that protostellar disk dynamics depends so heavily on protostellar disk chemistry."

I believe this is the academic world reaching for straws. Electrons do what they do best - they cling on to atoms and molecules without elevated temperatures. Should there be any reason for electrical currents and magnetic fields in the regions of protoplanetary formations ? I see none unless there are high enough temperatures for plasma environments.

3/24/2011

[rstevenson]

From the recent book Astrophysics of Planet Formation by Philip J. Armitage of U of Colorado...

... even apparently negligible ionization fractions suffice to couple magnetic fields dynamically to the gas, and this coupling in turn may be a critical element that permits angular momentum transport and accretion.

Armitage shows that both thermal and non-thermal ionization are available as mechanisms within the protoplanetary disk, with the possible sources of non-thermal ionization being "stellar X-rays, cosmic rays, and radioactive decay of nuclides".

I'm just now getting into the book and may not fully grasp the context of what I've quoted. But so far, it seems to be a book you'd find interesting Doug.

Rob

[dougettinger]

Rob,
I have not thought of non-thermal ionization. But don't electrons from beta decay easily and quickly find another atom with an room in the outer electron shell ? I will check out the book if it is not too cramed with mathematics.

3/24/2011