Sun's Temperature: Is the Sun Charged?

[Vinay R Hegde]

The temperature of the sun is so high that the matter exists in plasma state.At such high temperatures electrons are not bound to the atoms.Does it mean that the sun is charged? If the sun is neutral, where do the electrons reside?

 

[Drakkith]

The electrons are part of the plasma.

 

[BadBrain]

All in all, I would say that the sun is positively charged. The solar wind consists primarily of electrons and photons, per http://en.wikipedia.org/wiki/Solar_wind, so that would tend to leave a lot of protons and neutrons (in the form of hydrogen and helium nuclei) behind to positively charge the sun.

As per the joke:

Two hydrogen atoms were walking down the street. The first hydrogen atom says "I've just lost an electron!"

The second says: "Are you sure?"

The first answers: "I'm positive!"

 

[Dotini]

The solar wind consists primarily of electrons and photons, per http://en.wikipedia.org/wiki/Solar_wind

Dear BadBrain,

The source you cited actually says the solar wind consists of electrons and protons, not photons. Protons are probably the most interesting part of the solar wind, since these are the particles that accelerate faster the farther they move away from the sun - very exciting and puzzling, and a demanding problem!

Respectfully yours,
Steve

 

[BadBrain]

Dear BadBrain,

The source you cited actually says the solar wind consists of electrons and protons, not photons. Protons are probably the most interesting part of the solar wind, since these are the particles that accelerate faster the farther they move away from the sun - very exciting and puzzling, and a demanding problem!

Respectfully yours,
Steve

OK, so I misread the piece. That doesn't change the fact that the solar wind consists of more electrons than atomic nuclei, as per:

"The Sun's corona, or extended outer layer, is a region of plasma that is heated to over a million degrees Celsius. As a result of thermal collisions, the particles within the inner corona have a range and distribution of speeds described by a Maxwellian distribution. The mean velocity of these particles is about 145 km/s, which is well below the solar escape velocity of 618 km/s. However, a few of the particles achieve energies sufficient to reach the terminal velocity of 400 km/s, which allows them to feed the solar wind. At the same temperature, electrons, due to their much smaller mass, reach escape velocity and build up an electric field that further accelerates ions - charged atoms - away from the Sun.[18]"

Need I further remind you that at least some of the photons emitted by the sun are emitted as the result of electrons striking matter via the photoelectric effect, in which the entire energy of the colliding electron is imparted to the released photon?

I'm not trying to posit myself as some great astrophysicist, as I've been studying astrophysics for approximately two weeks now, as a consequence of my attempt to understand our own solar system and associated birth cluster. It doesn't matter to me how much younger than me you happen to be. I'm on this forum to learn all I can and to teach what I can.

 

[mfb]

Using the escape velocity of 618 km/s: A charge of just ~200 C would give a flat potential for protons (electric repulsion = gravitational attraction) (WolframAlpha). This is a high upper limit for the solar charge. For a negative charge, the limit is about -0.1C, as they are lighter by a factor of 2000.

Even if the effect BadBrain mentioned is important (I cannot judge this), the total charge of the sun has to be small.

 

[Drakkith]

OK, so I misread the piece. That doesn't change the fact that the solar wind consists of more electrons than atomic nuclei, as per:

"The Sun's corona, or extended outer layer, is a region of plasma that is heated to over a million degrees Celsius. As a result of thermal collisions, the particles within the inner corona have a range and distribution of speeds described by a Maxwellian distribution. The mean velocity of these particles is about 145 km/s, which is well below the solar escape velocity of 618 km/s. However, a few of the particles achieve energies sufficient to reach the terminal velocity of 400 km/s, which allows them to feed the solar wind. At the same temperature, electrons, due to their much smaller mass, reach escape velocity and build up an electric field that further accelerates ions - charged atoms - away from the Sun.[18]"

I don't believe this says that electrons make up more of the solar wind, it says that the electrons are more easily accelerated to a higher velocity, allowing them to escape easier, creating a charge that explains the acceleration of ions out into the solar wind. The charge on the Sun is very close to neutral, as a charge would not allow the oppositely charged particles to escape until neutral was reached again.

Need I further remind you that at least some of the photons emitted by the sun are emitted as the result of electrons striking matter via the photoelectric effect, in which the entire energy of the colliding electron is imparted to the released photon?

I don't see how this is relevant to the thread.

I'm not trying to posit myself as some great astrophysicist, as I've been studying astrophysics for approximately two weeks now, as a consequence of my attempt to understand our own solar system and associated birth cluster. It doesn't matter to me how much younger than me you happen to be. I'm on this forum to learn all I can and to teach what I can.

Who said anything about how old anyone was?

 

[Dotini]

...the total charge of the sun has to be small.

The charge on the Sun is very close to neutral...

There are no current measurements made in the vicinity of any star, including our own sun. I think the plasma physics are not well enough worked out to even give a theoretical current value for what is observed. 50 years and a new fleet of spacecraft are probably needed to get this answered.

Accepting that the sun is an electrical eunuch, we are left begging for an explanation of how protons are accelerated to near light speeds. Somehow, nature has contrived something like a rail gun to accelerate those heavy ions at us in flare/CME events.
http://www.nasa.gov/mission_pages/stereo/news/stereo_astronauts_prt.htm

Respectfully submitted,
Steve

 

[Drakkith]

There are no current measurements made in the vicinity of any star, including our own sun. I think the plasma physics are not well enough worked out to even give a theoretical current value for what is observed. 50 years and a new fleet of spacecraft are probably needed to get this answered.

It is my understanding that it MUST be very close to neutral as a whole or there would be obvious effects from a very strong electric field. Of course the Sun is very very large, and I'm guessing that there are various mechanisms that affect the charge of different parts of it.

 

[Dotini]

It is my understanding that it MUST be very close to neutral as a whole or there would be obvious effects from a very strong electric field. Of course the Sun is very very large, and I'm guessing that there are various mechanisms that affect the charge of different parts of it.

Totally agree, Drakkith. I appreciate your input very much.

With respect to the sun's size, I expect it would be most accurate to say it extends to the heliopause.

With respect to the different parts of it, altitudes, latitudes, fierce conditions and all, that's why I'm guessing at my 50 year figure to adequately quantify it.

Respectfully,
Steve

 

[Drakkith]

Hmmm. I personally wouldn't extend it out to the heliosphere, but that's just me.

 

[vociferous]

If the sun were losing more electrons than protons, eventually the charge would reach a point where it would be very difficult for any more electrons to escape.

Obviously, it must be in some kind of equilibrium state. You could model the sun as a equilibrium balance between gravitational force and electromagnetic force and find the equilibrium state where it allows protons and electrons to escape at the same rate. That would likely give you a theoretical prediction of the charge of the sun.

The key assumption is that the charge of particles escaping from the sun must be net neutral in the long run.

 

[Dotini]

It would appear there is some kind of variable charge exchange proceeding at the complexly structured boundary of the sun (heliopause) with the very local interstellar medium (VLISM). In situ measurements are needed to resolve the many riddles.

http://adsabs.harvard.edu/abs/2011AcAau..69..767M
The ongoing Voyager Interstellar Mission (VIM) and recent observations from the Interstellar Boundary Explorer (IBEX) and Cassini missions are providing significant new information about the interaction of the heliosphere with the very local interstellar medium (VLISM). With new observations have come significant new puzzles for describing the interaction physics. Direct measurements of the shocked, solar-wind flow speed are now possible (from Voyager 2) and show the flow remains supersonic. This is one more piece of evidence supporting the idea that the bulk of the energy density in the plasma resides in a non-thermal component that extends to very high energies. There are both quantitative and qualitative implications for the overall heliospheric structure. Observations of energetic neutral atoms (ENAs) by IBEX (in Earth orbit) from the interaction region(s) of the solar wind and the VLISM show unexpected structure on a variety of scales. In addition to the general “glow” of the sky in ENAs, IBEX data show a relatively narrow “ribbon” of atomic hydrogen emission from ∼200 to ∼6 keV, roughly circular, but asymmetric in intensity, and centered on an ecliptic longitude ∼221 degrees and ecliptic latitude of 39 degrees. The ribbon may be ordered by the interstellar magnetic field. It passes through, rather than being centered on, the “nose” from which the local, neutral interstellar wind enters the Heliosphere, indicating that the flow is not the primary driver of the system as had been thought previously. The neutrals from both the glow and ribbon are also characterized by non-thermal distribution functions. ENAs are observed at higher energies as well by the Ion and Neutral Camera (INCA) on Cassini (in orbit about Saturn). A “belt” of emission, broader than the ribbon but similar to it, is seen up to ∼50 keV. These observations emphasize the need for in situ measurements to understand the global nature of our local galactic environment, which is much more complex than previously thought. Only an interstellar probe with modern instruments and measurement requirements better defined by these recent observations can provide the new information required.

Respectfully submitted,
Steve

 

[Dotini]

The key assumption is that the charge of particles escaping from the sun must be net neutral in the long run.

"The solar wind is electrically balanced."

"The composition of the solar wind is a mixture of materials found in the solar plasma, composed of ionized hydrogen (electrons and protons) with an 8% component of helium (alpha particles) and trace amounts of heavy ions and atomic nuclei: C, N, O, Ne, Mg, Si, S, and Fe ripped apart by heating of the Sun's outer atmosphere, that is, the corona (Feldman et al., 1998).

SOHO also identified traces of some elements for the first time such as P, Ti, Cr and Ni and an assortment of solar wind isotopes identified for the first time: Fe 54 and 56; Ni 58,60,62 (Galvin, 1996)."
http://solar-center.stanford.edu/FAQ/Qsolwindcomp.html

Respectfully submitted,
Steve

 

[Dotini]

It is my understanding that it MUST be very close to neutral as a whole or there would be obvious effects from a very strong electric field.

http://spaceweather.com/ <--archive 7/24/2012
Here's an interesting, current report of a CME now accelerating away from the sun at 3400 km/sec, or 7.6 million mph. Yesterday it was reported at 2930 km/sec, so it is indeed accelerating. This class of event is said to occur only once or twice in any 10 year period. I'm wondering , what else but a very strong electric field can achieve this effect? Some kind of electric field must be a given, since changing magnetic fields produce electric fields, and the sun is a cauldron of magnetism and constant changes. But this is not to imply that the sun is not net neutral.

Respectfully submitted,
Steve

 

[twofish-quant]

I think the plasma physics are not well enough worked out to even give a theoretical current value for what is observed. 50 years and a new fleet of spacecraft are probably needed to get this answered.

It actually is. One of the basic results of plasma physics is that at lengths greater than the Debye length and at time scales that are longer than the plasma frequency, things are electrically neutral. You can show that any charge that is larger than either these two numbers is going to get canceled out.

Accepting that the sun is an electrical eunuch, we are left begging for an explanation of how protons are accelerated to near light speeds.

Magnetic fields. You have huge movements of charged particles in plasma, but those are balanced by charges moving in the opposite direction. So you can accelerate protons to huge velocities, but those have to be balanced by electrons moving in the other direction.

You can do plasma physics using a "two fluid" model or with an MHD approximation.

 

[twofish-quant]

Some kind of electric field must be a given, since changing magnetic fields produce electric fields

But constant ones don't. In most astrophysical objects, you end up with huge magnetic fields, but very weak electrical ones. What happens is that the moment you have any sort of electric field, then the charges will rearrange themselves to cancel out the field, so at anything that is larger than the atomic level, you have zero electric field.

In some situations the requirement of zero electric field causes the magnetic field to get "frozen" with the material. In that situation, you end up with incredibly complicated magnetic fields whose strength increases until you end up with a "short circuit" and this causes things like sunspots.

 

[twofish-quant]

If the sun were losing more electrons than protons, eventually the charge would reach a point where it would be very difficult for any more electrons to escape.

This is a cool problem set question. If you work out the numbers, then it turns out that at anything larger than atomic scales, things are electrically neutral. There's an equlibrium length and an equlibrium time

http://farside.ph.utexas.edu/teaching/plasma/lectures/node7.html (Debye length)

http://farside.ph.utexas.edu/teaching/plasma/lectures/node6.html (plasma frequency)

Both are at the atomic scale.

 

[Dotini]

But constant ones don't. In most astrophysical objects, you end up with huge magnetic fields, but very weak electrical ones. What happens is that the moment you have any sort of electric field, then the charges will rearrange themselves to cancel out the field, so at anything that is larger than the atomic level, you have zero electric field.

In some situations the requirement of zero electric field causes the magnetic field to get "frozen" with the material. In that situation, you end up with incredibly complicated magnetic fields whose strength increases until you end up with a "short circuit" and this causes things like sunspots.

Perhaps there is a controversy as to the existence of electric fields in astrophysical objects?
I am easily able to find numerous references to ongoing research in seminars, current and planned NASA missions to study electric fields on the sun and in Earth's magnetosphere.
http://sprg.ssl.berkeley.edu/seminars_091311.html
http://solar.physics.montana.edu/qiuj/publication/apj_acc.pdf
http://www.nasa.gov/mission_pages/rbsp/news/electric-atmosphere.html
http://mms.gsfc.nasa.gov/mission_details.html
http://naca.larc.nasa.gov/search.jsp?R=19800031774&qs=N=4294129240+4294957549+4294768863
http://ntrs.nasa.gov/search.jsp?R=20120007487

Even to a retiree/hobbyist like me, it seems to be the most basic science that if you want to accelerate a charged particle, the easiest and most obvious way to do it is with an electric field. If there is doubt or debate as to electric fields in space, it would be appreciated if both sides of the argument could be (politely) discussed here at PF, the most respected physics discussion board in the internet.

Respectfully submitted,
Steve

 

[tasp77]

Hope I remember this correctly,

Asimov calculated in one of his excellent science essays around a pound (love those English measures) of electrons somehow removed from Earth and added to the sun would drastically alter the Earth's orbit from around it.

I think as alluded to earlier in the thread, Asimov was just emphasizing the strength of the charge of the electron compared to the strength of gravity.

Despite the suns energy and turbulence, it would have to be electrically neutral or as noted, we would measure significant effects.

 

[twofish-quant]

Perhaps there is a controversy as to the existence of electric fields in astrophysical objects?

No controversy, just someone in physics forums (me) misremembering stuff and explaining things badly.

What I was misremembering was that in the MHD approximation, charge cancellation causes the electric field in the rest frame of the fluid as zero,

http://math.nyu.edu/mfdd/strauss/fem7pl/node2.html

However in another frame of reference, that results in an electric field. Also, the MHD approximation will tend to generate magnetic fields that are large enough so that the approximation will break down.

This is different from asking if the sun is charged.

Even to a retiree/hobbyist like me, it seems to be the most basic science that if you want to accelerate a charged particle, the easiest and most obvious way to do it is with an electric field.

The thing about electric and magnetic fields is that they are interchangeable. Relativity says that whether something is magnetic or electric depends on the frame of the observer. The MHD approximation says that you have zero electric field in the frame of the fluid, but since the fluid is moving that gives you electric fields in another frame.

 

[vociferous]

This is a cool problem set question. If you work out the numbers, then it turns out that at anything larger than atomic scales, things are electrically neutral. There's an equlibrium length and an equlibrium time

http://farside.ph.utexas.edu/teaching/plasma/lectures/node7.html (Debye length)

http://farside.ph.utexas.edu/teaching/plasma/lectures/node6.html (plasma frequency)

Both are at the atomic scale.

That is interesting because my first instinct is that the sun might reach a positively charged equilibrium state due to the mass difference of electrons and protons.

However, it seems that the mass difference is accounted for in the electrons having a greater rms speed instead. This seems odd to me because I would assume the escape velocity from the corona is the same for all particles, so I think there is something I am missing, as I know only a little about the inner-dynamics of a plasma in a gravitational field.

 

[twofish-quant]

However, it seems that the mass difference is accounted for in the electrons having a greater rms speed instead. This seems odd to me because I would assume the escape velocity from the corona is the same for all particles, so I think there is something I am missing, as I know only a little about the inner-dynamics of a plasma in a gravitational field.

EM is *much* stronger than gravity, so even if gravity tells electrons that they can escape, EM keeps them from doing so. Electrons have a much higher rms than protons because they are lighter, but EM is strong enough to prevent charge separation.

 

[Brett32324]

Dear BadBrain,

The source you cited actually says the solar wind consists of electrons and protons, not photons. Protons are probably the most interesting part of the solar wind, since these are the particles that accelerate faster the farther they move away from the sun - very exciting and puzzling, and a demanding problem!

Respectfully yours,
Steve

I believe those particles are one of the keys to anti-gravity technologies and reversing the force of gravity in general...

 

[Drakkith]

I believe those particles are one of the keys to anti-gravity technologies and reversing the force of gravity in general...

This is not possible if our current understanding of nature is accurate, and discussions of anti-gravity are not allowed on PF per the rules.