Hot fusion puzzle

[dalemiller]

Whereby hot fusion in stars does not lead to explosive regeneration, it would seem that it must not be self-sustaining and therefore must depend upon a companion source of heat. Can anybody help me to get that notion out of my head?

[pioneer]

Since we can't directly observe the core of a star, one can only guess. My guess is there is both forward and reverse fusion/fission reactions, with forward slightly favored. Unlike a hydrogen bomb which can separate distances to inhibit reversal, a stella core is very high pressure keeping products closer. If it was only forward, one would expect stars to act like huge H-bombs, with the fusion process accelerating as the amount of activation energy accelerates. But if we remove heat/energy fast enough, we can inhibit a runaway burn. The easiest way is to increase the mass/energy of the some of the products back to reactants, since they are at the correct parameters to absorb. There is no waste, since these will go forward, eventually.

[Mr Skeptic]

Hot plasma is less dense, less dense plasma has less fusion reactions, plasma cools off by emitting radiation, gravity compresses the plasma. It all balances out, except when it doesn't.

[swansont]

Since we can't directly observe the core of a star, one can only guess.

 

No, no, no, and might I add, no. Science is not guesswork.

 

Whereby hot fusion in stars does not lead to explosive regeneration, it would seem that it must not be self-sustaining and therefore must depend upon a companion source of heat. Can anybody help me to get that notion out of my head?

 

Fusion of light isotopes releases energy. Why would it need a companion source of heat? What it needs is confinement, which is provided by gravity.

[dalemiller]

 

Fusion of light isotopes releases energy. Why would it need a companion source of heat? What it needs is confinement, which is provided by gravity.

 

[If hot fusion were the sole source of heat, then if it could keep its own temperature high enough for sustained fusion then such a point would be unstable, like a dime standing on its edge. Any spike of increased fusion would produce higher temperature with an avalanching effect destructive to ecology. In other words, it operates with positive feedback, the nemesis of control. The nature of such fusion would likely be a random distribution of minute events tending to present relatively modest contributions of temperature increase throughout a broad volume of fuel. Such a broad warming of so much matter might well offer slight enough a temperature to fall short of self-sustaining operation.

 

It seems plausible that some other "torch" might be required to prevent such fusion from cycling down. This gives us two factors to suppose that hot fusion gets a little help: The second factor being that stars like our sun offer rather consistent output energy, implying that it is governed by significant negative feedback certainly lacking with hot fusion.

 

If somehow, a cold fusion process were somehow going on somewhere in such a star, we would have our torch to keep up temperature in our plasma, and we would have natural negative feedback to regulate the stellar output. (Static squeeze accomplishing cold fusion would find increased opposition as fuel temperature rises bringing the process rate to a saddle point.)

Edited November 25, 2010 by dalemiller

[Klaynos]

Gravity, and the associated pressure are the torch to which I think you are referring. Our understanding of the suns fusion process is very good.

[dalemiller]

Gravity, and the associated pressure are the torch to which I think you are referring. Our understanding of the suns fusion process is very good.

Then you must be someone who could help me in my confusion. Does the sun utilize any cold fusion? My understanding of the sun's fusion process is not very good so I am asking for some of yours.

[swansont]

When the plasma heats up, it tends to expand, and that would cause it to cool. This provides the negative feedback necessary to maintain steady-state. Gravity counters the expansion due to heating.

[dalemiller]

When the plasma heats up, it tends to expand, and that would cause it to cool. This provides the negative feedback necessary to maintain steady-state. Gravity counters the expansion due to heating.

 

Am grateful for your acknowledgement of vital need for negative feedback within stellar fusion processes.

 

Surely you jest with your proffered provision for negative feedback, but your assurance of such need by stellar fusion should lead some bright young scientists to the static pressure process that does serve that purpose.

 

Thanks to you, I think my work is done.

Edited September 9, 2010 by dalemiller

[swansont]

Surely you jest with your proffered provision for negative feedback

 

Not at all. Fusion is exothermic, PV=nRT, and fusion rates are strongly dependent on temperature.

 

http://cass.ucsd.edu/public/tutorial/StevI.html

 

Section 3

 

A good way to see the stability of this equilibrium is to consider what happens if we depart in small ways from equilibrium: Suppose that the amount of energy produced by nuclear reactions in the core is not sufficient to match the energy radiated away at the surface. The star will then lose energy; this can only be replenished from the star's supply of gravitational energy, thus the star will contract a bit. As the core contracts it heats up a bit, the pressure increases, and the nuclear energy generation rate increases until it matches the energy required by the luminosity.

Similarly, if the star overproduces energy in the core the excess energy will heat the core, increasing the pressure and allowing the star to do work against gravity. The core will expand and cool a bit and the nuclear energy generation rate will decrease until it once again balances the luminosity requirement of the star.

[dalemiller]

OK, I under looked hot fusion's negative feedback path. It had looked as though a flat-footed fresh attack was available as simple evidence demanding cold fusion at the solar core. My blunder does not validate contentions that hot fusion does exist in the core, but it does repair my humility. (Unwarranted self deprecation.) In that our moderator's paraphrasing of feedback knocked me so very far off the track, I do offer my crack at the wording. (I thought he was freezing up a block of ice with a flamethrower.)

 

The negative feedback for hot stellar fusion occurs as follows: For an inifitesimal increase from normal temperature of plasma at a given strata, a small increase in energy production results. Whereby some of that energy takes the form of heat, expansion due to that increased heat causes much of the increased energy to become diverted into storage as potential energy in the consequential elevation of stellar matter above that position. Attenuation of decreases from normal temperature is accomplished by supplementation of retarded fusion with thermal energy released by corresponding descent of overbearing matter into the contracting volume produced by under temperature.

Edited September 13, 2010 by dalemiller

[dalemiller]

 

some bright young scientist said:

A good way to see the stability of this equilibrium is to consider what happens if we depart in small ways from equilibrium: Suppose that the amount of energy produced by nuclear reactions in the core is not sufficient to match the energy radiated away at the surface. The star will then lose energy; this can only be replenished from the star's supply of gravitational energy, thus the star will contract a bit. As the core contracts it heats up a bit, the pressure increases, and the nuclear energy generation rate increases until it matches the energy required by the luminosity.

Similarly, if the star overproduces energy in the core the excess energy will heat the core, increasing the pressure and allowing the star to do work against gravity. The core will expand and cool a bit and the nuclear energy generation rate will decrease until it once again balances the luminosity requirement of the star.

 

 

That ostensible feedback claimed for hot fusion doesn’t compare with the full-bodied negative feedback apparent for cold fusion static pressure induced fusion within a core of nuclear fuel. We needn’t waste time with contradiction of “heating something makes it get cooler” comment. Floating that spin would be a real piece of work. The juggling of energy between temperature deviation thermal input augmentation and vertical displacement remains a concession here, but the smoothing out of luminosity seems more of a filtering job than that of regulation. The kicker to such smoothing comes upon contemplation of the venue: a given temperature is sought for a thin shell of plasma within a star. Simultaneous compensation for a circle of under-temperature and a surrounding ring of over temperature of such a shell would provide a gravity-proof nullification of net expansion/compression exchange that might explain how a sunspot works. A raging over temperature in that ring enclosing a dropout of fusion in the middle could amount to quite a scuffle. There is no need here to get into conjecture upon solar flares, but I did it anyhow. For the first time it makes sense that a spotted sun should give out extra heat.

 

(Comprehension subsequent to this posting entailed, not any negative feedback in fusion of plasma, but rather a circumvention of regeneration by translation of increased thermal energy into the potential energy domain instead of advanced temperature prone toward explosive regeneration.)

 

Meanwhile, it is a great relief to believe that cold fusion serving within the central core would calmly tone down such flare-ups by restraint with its full-fledged negative feedback that so easily retards supporting preheating of the surrounding plasma.

 

Come to think about it, all it should take to get one of those sun spots going would be a nice little vortex. Or maybe a great big one. The central vertical axis of such spinning plasma would decompress a little, thus cooling the middle with regenerative influence upon the consequential declining rate of fusion, and centrifugal force would compress, thus add heat to the outermost plasma, again with regenerative effect. The combined effect of this positive feedback sufficiently escapes the drag of gravity to avalanche to higher net luminosity, probably launching solar flares, but perhaps yet short of self sufficiency. We might wonder how deeply such a vortex might go: golly, maybe it goes down to the central core! As hot as the plasma gets, it seems not to heat up surrounding plasma as fast as such heat escapes. Meanwhile, the cold fusion that should be going on in the central core remains the only source with legitimate negative feedback. Bearing the lion's share of energy production, the solar core again seems the steady governor that warms us safely.

Someone will ask why there would be vortexes: What vortexes?. For anyone from planet Earth it should be a no-brainer.

Edited November 25, 2010 by dalemiller

[dalemiller]

Hot plasma is less dense, less dense plasma has less fusion reactions, plasma cools off by emitting radiation, gravity compresses the plasma. It all balances out, except when it doesn't.

 

It is respectfully suggested that If you follow preceding entries, you might want to retract your first twelve words quoted above.

Edited September 28, 2010 by dalemiller

[insane_alien]

why? hot plasma IS less dense if it's at the same pressure.

 

also, less dense plasma does have a lower rate of fusion.

 

plasma will also cool off when emitting blackbody radiation.

 

and gravity can compress plasma.

 

nothing he said is false.

[dalemiller]

why? hot plasma IS less dense if it's at the same pressure.

 

also, less dense plasma does have a lower rate of fusion.

 

plasma will also cool off when emitting blackbody radiation.

 

and gravity can compress plasma.

 

nothing he said is false.

 

Just a few of his first twelve words were false. How come nobody jumps in for me when I get picked on? Look at what the big kids have been saying on this thread. They talk up temperature as boosting fusion.

 

Dealing with hot fusion: Fusion increases with particle velocity AKA Plasma Temperature. More density great for cold fusion, but that happens somewhere else. Our taxes pay for crazy ground pounders trying to get plasma so hot in the lab that it will fuse, when I think we have a case for saying "you cannot get there from here." It doesn't get hot enough for that inside the sun. Runaway fusion at rims of sun spots goes on down below-decks because total volume can hold fast as hot gets hotter (out at the rim) and cool gets cooler (in the center). That odd-mans gravity right out of the equation. Nothing has to get lifted. I learned that because these guys showed me to be wrong on regenerative hot plasma buried far enough out of the swirl. Had to noodle out the sun spots just to get even.

Edited November 25, 2010 by dalemiller

[insane_alien]

all other things being equal, fusion rates increase with temperature.

 

what matters for fusion is the numebr of particles that collide with enough momentum to overcome electrostatic repulsion barrier.

 

so, first off that means there is a minimum temperature before the particles will be able to fuse.

 

as for a given temperature there is a distribution of momentums, the hotter, the more of this distribution is above the lower limit for fusion.

 

ALSO, the higher the temperature(and pressure) the more collisions there are.

 

so for high fusion rates you want high temperatures and high pressures.

 

 

now for the sun. The core of the sun is roughly constant pressure. So, if the core heats up due to an excess amount of fusion it EXPANDS. When it expands it COOLS so more of the momentum distribution is below the barrier and it gets less DENSE so there are fewer collisions. this results in a decrease in fusion rates. Is this really so hard to understand?

 

also, cold fusion is in no way shape or form confirmed. I honestly don't know why you keep on harping on about it.

[dalemiller]

 

So, if the core heats up due to an excess amount of fusion it EXPANDS. When it expands it COOLS so more of the momentum distribution is below the barrier and it gets less DENSE so there are fewer collisions. this results in a decrease in fusion rates. Is this really so hard to understand?

 

I don't understand why you are referring to the core when addressing hot fusion. You explain that when the core heats up it EXPANDS, this expansion COOLS it. Then I must suppose that such COOLING causes it to contract which will HEAT it which will cause it to EXPAND which will COOL it which will CONTRACT it which will HEAT it which will EXPAND ...................

[granpa]

consider a similar case with an orbiting satellite.

If you add energy with thrusters then you would expect it to go faster

What actually happens is that it goes to a higher orbit where it actually goes slower.

so adding energy makes it go slower.

its very non-intuitive.

Edited September 25, 2010 by granpa

[insane_alien]

dale, please, look up the concept of equilibriums. and not just the definition of it. go into some detail on what actually happens.

 

and yes, it can contract and heat up. this will happen if there is a drop in fusion rates(such as casued by an over expansion).

 

its only really a cyclical process like that in variable stars. most stars have reached a stable equilibrium where the fusion rate is near constant so the core isn't expanding or contracting very much.

 

stellar dynamics are complicated because you need to pull in models from all sorts of fields. from fluid mechanics to high energy physics. trying to simplify this down to a few forum posts for someone unrelated to the field would be impossible. there are many many papers on stellar dynamics and most relate only to one aspect of the fusion process in stars. it's only when physicists model the internal dynamics of a star do they all come together, but to do that requires a super computer. and even then it requires multiple people to contribute the equations from their own particular expertise to make the complete model.

 

on the plus side we get cool movies like this

(shows an example of when equilibrium is broken.

[dalemiller]

dale, please, look up the concept of equilibriums. and not just the definition of it. go into some detail on what actually happens.

 

and yes, it can contract and heat up. this will happen if there is a drop in fusion rates(such as casued by an over expansion).

 

its only really a cyclical process like that in variable stars. most stars have reached a stable equilibrium where the fusion rate is near constant so the core isn't expanding or contracting very much.

 

stellar dynamics are complicated because you need to pull in models from all sorts of fields. from fluid mechanics to high energy physics. trying to simplify this down to a few forum posts for someone unrelated to the field would be impossible. there are many many papers on stellar dynamics and most relate only to one aspect of the fusion process in stars. it's only when physicists model the internal dynamics of a star do they all come together, but to do that requires a super computer. and even then it requires multiple people to contribute the equations from their own particular expertise to make the complete model.

 

 

 

Most of the fun I have found in science has been in finding ways to simplify comprehension. Such trains of thought can catch on to spread like wildfire for a lazy, simple person predisposed to seek more comfortable ways to rest. There are two kinds of people in this world: those of us who want things easier, and those of you who seek to make everything more difficult. I salute your ambition, but prefer to emulate the peaceful demeanor of the sloth.

 

If you were to examine other entries in this string, you would find another professional scientist advancing the manner in which hot fusion avoids excess regeneration. His contribution acknowledged hot fusion rate to increase with temperature. I learned from him of how such potential positive feedback is suppressed, but wonder why you do not assault his words as you do mine. It occurs to me that you may seek more vulnerable prey to bully with your fine education.

 

Nevertheless, I invite your attention to my humble attempt to reword an explanation of hot stellar fusion to such form that we ordinary folks can more readily understand. Bear with me and you will be glad for that when you get a little older.

 

At whatever given stellar depth hot fusion might be occurring, the gas pressure will hardly be affected by any slight change in temperature, and can thus be ordinarily ignored as a dynamic factor influencing the population density of proton fuel. A very slight increase in temperature due to an event of hydrogen fusion, for instance, represents a significant increase for local proton velocity to the extent that rate of fusion will rise. This would be an inherently regenerative situation if it were not for the fact that gas expansion incidental to temperature rise typically absorbs the additional energy by supplying lifting force upon the overbearing matter above. Thus, energy invested as potential energy detracts significantly from the amount of energy results in heat form with the increased rate of fusion.

 

Note that global distribution of gravitational heating is accomplished by the miniscule increase of depth responding to such gas expansion to extend a general uniformity of luminosity. The decentralized locality of any spot of any strata thus shares its disposition into a common overview.

 

Assuming that stellar matter would be affected by rotational formations at least as surely as with earthly atmosphere and oceans, then we must expect vortexes to be the source of Sol's familiar sun spots due to immediate proximity of low pressure central and high pressure surrounding regions of plasma fuel. At any strata enduring fusion, a lateral pressure gradient between these regions would bring a limited amount of unbridled regenerating fusion surrounding an inner circle of of diminished fusion such that no lifting of overbearing mass intervenes. Plasma contraction within that matches expansion from without would produce a "chilled" center rimmed by overheated plasma.

Edited November 25, 2010 by dalemiller

[dragonstar57]

so what would a powerful energy pulse do to the sun? ie if somehow a large mass of antimatter collided it. what would a huge variation in solar energy do to the suns equilibrium. would it begin to oscillate between high and low energy output until it settled at its equilibrium again?

[dalemiller]

so what would a powerful energy pulse do to the sun? ie if somehow a large mass of antimatter collided it. what would a huge variation in solar energy do to the suns equilibrium. would it begin to oscillate between high and low energy output until it settled at its equilibrium again?

Am unable to deal with antimatter in this lifetime. As to huge swings in solar energy, I need first merely withdraw my earlier ignorance in reference to unbridled fusion. At the site of a sunspot, (fancy a "cold spot" [some 4500 Kelvins] a big enough dimple into which our planet could be nested], a raging "cylinder" of over-intense fusion is capped by how much draft is afforded by contracting volume within). Finite cooling rates from within the vortex would seem the gating factor of the supplemental fusion encountered in surrounding plasma. Existing scientific conjecture that magnetic flux produces sunspots might be relegated to being an effect rather than a cause. Reported variation of solar rotation rates with latitude suggests extreme whirlpool activity accounting for the vortexes seen here as underlying cause for sunspots.

 

Now, addressing your question, a huge variation would just fry us if we haven't done it already by then, so not to worry. As perhaps the only astrophysicist who is sure that our core fusion is cold static fusion not of plasma, then my presumption would hold as plausible that a proton core would respond to severe change by shutting down its output, perhaps to quench a lot of trouble. On the other hand, a big disturbance might deal a long lasting array of solar vortexes to do just as you suggest.

Edited December 14, 2010 by dalemiller

[Klaynos]

Our gravity - hot fusion models of the sun match very well with experimental evidence. You're going to have to beat that to get anyone to take you seriously, the first step is understanding the existing models. I'd suggest at the very least reading something like Phillips A.C. (1999), The Physics of Stars... Or for preference a physics degree skewed towards astrophysics. This stuff isn't easy people spend their lives trying to understand it.

[dragonstar57]

so what would a powerful energy pulse do to the sun? ie if somehow a large mass of antimatter collided it. what would a huge variation in solar energy do to the suns equilibrium. would it begin to oscillate between high and low energy output until it settled at its equilibrium again?

the antimatter idea was just an example of how something like this could occur.

if the temperature of the sun suddenly jumped the sun would expand.

that would cause it's fusion reaction to slow down and cool again.

which would cause it to heat up

and back and fourth and back and fourth

until it reached its equilibrium again correct?

[dalemiller]

Our gravity - hot fusion models of the sun match very well with experimental evidence. You're going to have to beat that to get anyone to take you seriously, the first step is understanding the existing models. I'd suggest at the very least reading something like Phillips A.C. (1999), The Physics of Stars... Or for preference a physics degree skewed towards astrophysics. This stuff isn't easy people spend their lives trying to understand it.

 

Thanks to a contribution from Swanson, I was not only enlightened that stellar hot fusion does not go unbridaled, but he had led me to where I could discover the cause of sun/star spots and solar/stellar flares. Another feather in my hat seems no cause for dragging these old bones back to school as you propose. Not to be ungrateful, but Swanson certainly did provided me a case against emulation of professional explanations. There is no way I can ever say that when plasma is heated it gets colder because of the consequential expansion of the gas. I promise not to. Another scientist spoke just the very same words as he but I still thank my creator for sparing me that capability.

 

In a nutshell, an isolated incident of overtemperature increases rate of fusion, but most additional energy thus produced is absorbed as potential energy in the lifting of the overbearing plasma thus displaced by the consequential gas expansion. Such stored energy returns as heat to supplement an incident of undertemperature. However, when simultaneous undertemperature of fusing plasma occurs in conjunction with nearby overtemperature plasma, then additional energy production is accorded to the hot stuff as it expands directly into the cold stuff. Such activity is normal in the presence of a vortex which thus produces a sun/star spot with solar/stellar flares rising from the encircling hot stuff. A steady rise of electrons (presumably resulting from cold static fusion running in the central core) follows along the solar flares to produce the magnetic activity presently mistaken as somehow or other causing the sun/star spots.

 

the antimatter idea was just an example of how something like this could occur.

if the temperature of the sun suddenly jumped the sun would expand.

that would cause it's fusion reaction to slow down and cool again.

which would cause it to heat up

and back and fourth and back and fourth

until it reached its equilibrium again correct?

 

Ask Klaynos. I'm sposed to shut up and go read a book. He must indeed know an awful lot except for the polarity of stellar cores. That little secret which I am trying not to keep is the reason I call myself an astrophysicist (self educated, self employed, self anointed). It is just playing with a full deck that makes all the difference.

Edited December 14, 2010 by dalemiller