Why Doesn't The Sun Explode (Or Expand)?

[johnferk]

I had previously asked the question "Is there gravity at the center of a sphere?" and the sum of the answers was "no." I.e., in a sphere of uniform density there is some point "X" within the sphere where the sum of the mass in the region [X to the surface of the sphere] exceeds the sum of the mass in the region [X to the center of the sphere] and the "gravitational pull" should invert and become directed to the outer surface of the sphere.

 

From some of the replies that were posted it seems the fundamental question (is there gravity at the center of a sphere?) is actually quite old and rather non-original. I can feel good about that since someone else (evidently Newton) thought of the problem before I did. Nothing wrong with that; I'm just a little tardy in my thinking.

 

OK - so now on to the next topic.

 

Everything I've ever read says that stars like the sun are stable because the "outward" force of energy derived from the fusion process counters the "inward" force of gravity. When the fusion process no longer balances the gravitational "pull", the star collapses.

 

What's bugging me now is this. As the energy derived from fusion transits outward past the point "X" where gravity is balanced, the sum of the fusion derived energy and the gravitational pull in the region [X to the surface of the sphere] will exceed the inward attraction of the "gravity" in the region [X to the center of the sphere]. Logically then, the sun should be expanding in the region [X to the surface of the sphere]. In the absence of that, you have to believe the "force" of gravity is unidirectional and directed toward the center of the sphere.

 

We all know that gravity is a mutually attractive event rather than unidirectional. Besides, if it were unidirectional, there would be gravity at the center of a sphere with uniform density.

 

That contradicts the answers posted to my original question.

 

Which is it (or what have I missed here)?

[CraigD]

I had previously asked the question "Is there gravity at the center of a sphere?" and the sum of the answers was "no."

Correct. More precisely, the force of gravity at the center of mass of a sphere, or any other body, is zero.

 

I.e., in a sphere of uniform density there is some point "X" within the sphere where the sum of the mass in the region [X to the surface of the sphere] exceeds the sum of the mass in the region [X to the center of the sphere] and the "gravitational pull" should invert and become directed to the outer surface of the sphere.

Incorrect.

 

... (or what have I missed here)?

You’ve missed the shell theorem, which explains why there is never be an outward-from-the-center gravitational force inside a sphere where the density is constant, or a function of the distance from the center of the sphere of each shell.

[Village Idiot]

 

 

 

Everything I've ever read says that stars like the sun are stable because the "outward" force of energy derived from the fusion process counters the "inward" force of gravity. When the fusion process no longer balances the gravitational "pull", the star collapses.

 

 

 

Rather than to make the most of what that explanation has to offer, the question "Why doesn't the sun explode?" might be answered without wading into doomsday.

 

Try this: There are two ways that hydrogen fusion provides a flow of stellar energy. They would be a static compression phenomenon within a central core, and a dynamic process accomplishing proton-to-proton collisions advancing in frequency with increase of temperature.

 

Core fusion:

Due to an electron shell surrounding the star, according to Newton's Shell Theorem, the sum total effective negative electrical charge positions itself fully to external locations as at the center of that spherical body. Within, that referred charge intensity reduces in direct proportion to reduction of positional radius. Counter-intuitively, that charge repels electrons away from the very same place that represents them all. Particles of positive charge (mostly hydrogen nuclei) are drawn toward that point to form a large, possibly hollow ball of nuclear fuel. Here, expansion resulting from temperature increase provides reliable negative feedback that finds a natural balance in determining a steady rate of energy production.

 

Plasma fusion:

External to the stellar central core and at any stellar radius within the outer core, there will be equilibrium of temperature and rate of energy production by fusion of plasma. Regulation is attained against the threat of avalanching rate of fusion, by the result of plasma expansion resulting from any excessive rate of fusion. An infinitesimal increment of excess rate of fusion transfers resulting heat from kinetic into potential energy by the necessary lifting process incidental to expansion of the medium. The only time that this fusion can avalanche toward an explosive rate of fusion is when a vortex at that radius precludes expansion. Such events account for stellar flares with accompanying star spots.

Edited December 31, 2012 by Heedless

[CraigD]

Heedless, don’t be heedless of our site rules! ;) Please back up your claims with links or references!

 

I believe if you are diligent in doing this, you’ll not make many of them, as you’ll find they’re incorrect. Catching mistakes before committing them to text is good for everybody.

 

Core fusion:

Due to an electron shell surrounding the star, according to Newton's Shell Theorem, the sum total effective negative electrical charge positions itself fully to external locations as at the center of that spherical body.

That’s not at all what the shell theorem, which Newton famously proved in the late 17th century, states. The theorem has nothing to do with atomic structure or charge – it requires only the classical gravity law, [math]F = G \frac{m_1 m_2}{r^2}[/math]. Newton didn’t know the structure of atoms, nor of the existence of neutrons, protons and electrons, because these wasn’t discovered ‘til the mid 19th century.

 

External to the stellar core, at any given radius there will be equilibrium of temperature and rate of energy production. Regulation is attained against the threat of avalanching rate of fusion, by the result of plasma expansion resulting from any excessive rate of fusion. An infinitesimal increment of excess rate of fusion transfers resulting heat from kinetic into potential energy by the necessary lifting process incidental to expansion of the medium. The only time that this fusion can avalanche toward an explosive rate of fusion is when a vortex at that radius precludes expansion. Such events account for stellar flares with accompanying star spots.

Best current theory of the structure of stars states that essentially no fusion occurs much outside of a star’s core. For example, for our Sun, no significant fusion is thought to occur beyond about 30% of its radius. (reference: wikipedia article sun)

 

Sunspots and solar flares are thought to be due to interaction of the Sun’s complicated and changing magnetic field its ionized (plasma) matter. (reference: wikipedia article solar flare)

[Guest MacPhee]

Even so, doesn't the Sun seem quite unrealistic.

 

It's supposed to be a gigantic thermonuclear ball of fusing hydrogen. Like a permanently-exploded H-bomb. Which continues to explode for billions of years! While exhibiting no signs of change - the sun's disc always remains exactly the same size.

 

Is that really credible. The Sun's hydrogen must be getting used up at a very fast rate. Shouldn't that make the solar disc shrink, or expand, or look a different colour, or change in some perceptible way.

 

Do telescopic observations of the Sun reveal any changes in its diameter or colour?

Edited December 27, 2012 by MacPhee

[CraigD]

Even so, doesn't the Sun seem quite unrealistic.

 

It's supposed to be a gigantic thermonuclear ball of fusing hydrogen. Like a permanently-exploded H-bomb. Which continues to explode for billions of years! While exhibiting no signs of change - the sun's disc always remains exactly the same size.

The important point I was trying to communicate in my previous post is that the Sun is not a “gigantic ball of fusing hydrogen”. It’s better described as a gigantic ball of convecting plasma heated by a small (by stellar standards, not human ones) amount of fusion occurring in its core.

 

Is that really credible[?] The Sun's hydrogen must be getting used up at a very fast rate. Shouldn't that make the solar disc shrink, or expand, or look a different colour, or change in some perceptible way.

To answer this question, it helps to use some numbers.

The mass of the Sun (M) is about 1.989 x 10³⁰ kg

The luminosity (power) of the Sun (P) is about 3.846 x 10²⁶ W

From this, and the mass-energy equivalence formula [math]E=\frac{m}{c^2}[/math], we can calculate the rate at which the Sun’s mass is decreasing due to hydrogen being fused into helium:

 

[math]\frac{\Delta M}{\Delta t} = \frac{P}{c^2} \dot= 4.279 \times 10^9 \,\mbox{kg/s}[/math]

 

Expressed as a fraction of its current mass, this is 2.142 x 10^-21/s, or 0.0000000000000000002142%/s.

 

The Sun is thought to be about 5,000,000,000 years old, and to have about 5,000,000,000 years (about 1.578 x 10¹⁷ s) in its present main sequence form (before it briefly becomes a red giant, then a very long-living white dwarf). So, multiplying its rate of mass loss due to fusion by this, we get that the Sun in its current form will lose about 0.0338% of its mass due to fusion.

 

Do telescopic observations of the Sun reveal any changes in its diameter or colour?

No.

 

Because the Sun’s outer layers vary in thickness, color, and luminosity from day to day, combined with its slow rate rate of evolution, and the very short (by astronomical standards) length of time which we’ve had precise instruments to watch it, we’ve not been able to directly observe its long-term evolution. It’s hard to precisely measure the diameter of a giant ball of magnetically whipped plasma. :)

 

Theoretical models of the Sun’s evolution tell us it will grow brighter and slightly larger for the next 5 billion year, but given its “noisiness”, many centuries of precise measurement will be needed to observationally confirm them. Most confirmation of these models comes from observing other stars which appear to be similar except for their age.

[Village Idiot]

 

That’s not at all what the shell theorem, which Newton famously proved in the late 17th century, states. The theorem has nothing to do with atomic structure or charge – it requires only the classical gravity law, [math]F = G \frac{m_1 m_2}{r^2}[/math]. Newton didn’t know the structure of atoms, nor of the existence of neutrons, protons and electrons, because these wasn’t discovered ‘til the mid 19th century.

 

 

I understand that. What Newton had in mind with the Shell Theorem, gravity, applies to electrostatic force as well. Both forces follow the inverse square law. Source: http://en.wikipedia.org/wiki/Shell_theorem states the following.

 

“In addition to gravity, the shell theorem can also be used to describe the electric field generated by a static spherically symmetric charge density, or similarly for any other phenomenon that follows an inverse square law. The derivations below focus on gravity, but the results can easily be generalized to the electrostatic force.”

[CraigD]

I understand that. What Newton had in mind with the Shell Theorem, gravity, applies to electrostatic force as well. Both forces follow the inverse square law. Source: http://en.wikipedia.org/wiki/Shell_theorem states the following.

 

“In addition to gravity, the shell theorem can also be used to describe the electric field generated by a static spherically symmetric charge density, or similarly for any other phenomenon that follows an inverse square law. The derivations below focus on gravity, but the results can easily be generalized to the electrostatic force.”

That’s correct. The shell theorem states that a phenomenon that follows an inverse square law ([imath]F = k r^{-2}[/imath]), experiences zero net force within a spherical shell of whatever exerts this force.

 

A body with mass anywhere within the volume of a uniform density shell experiences zero net force, so jwkref’s original reasoning that

in a sphere of uniform density there is some point "X" … the "gravitational pull" should invert and become directed to the outer surface of the sphere.

is proven incorrect.

 

A body with charge within a shell with uniform charge also experiences zero net force. However, the shell theorem does not prove that

Due to an electron shell surrounding the star, according to Newton's Shell Theorem, the sum total effective negative electrical charge positions itself fully to external locations as at the center of that spherical body. Within, that referred charge intensity reduces in direct proportion to reduction of positional radius. Counter-intuitively, that charge repels electrons away from the very same place that represents them all. Particles of positive charge (mostly hydrogen nuclei) are drawn toward that point to form a large, possibly hollow ball of nuclear fuel

No scientific theory, mathematical proof, or evidence of which I’m aware suggest that matter in stars, or any other plasma, segregates itself by charge, electrons on the outside, protons on the inside (rather like a gigantic atom).

 

Heedless, if you know of some source supporting you claim otherwise, please post links or references to them. If you don’t, don’t make such claims!

[Guest MacPhee]

The important point I was trying to communicate in my previous post is that the Sun is not a “gigantic ball of fusing hydrogen”. It’s better described as a gigantic ball of convecting plasma heated by a small (by stellar standards, not human ones) amount of fusion occurring in its core.

 

 

To answer this question, it helps to use some numbers.

The mass of the Sun (M) is about 1.989 x 10³⁰ kg

The luminosity (power) of the Sun (P) is about 3.846 x 10²⁶ W

From this, and the mass-energy equivalence formula [math]E=\frac{m}{c^2}[/math], we can calculate the rate at which the Sun’s mass is decreasing due to hydrogen being fused into helium:

 

[math]\frac{\Delta M}{\Delta t} = \frac{P}{c^2} \dot= 4.279 \times 10^9 \,\mbox{kg/s}[/math]

 

Expressed as a fraction of its current mass, this is 2.142 x 10^-21/s, or 0.0000000000000000002142%/s.

 

The Sun is thought to be about 5,000,000,000 years old, and to have about 5,000,000,000 years (about 1.578 x 10¹⁷ s) in its present main sequence form (before it briefly becomes a red giant, then a very long-living white dwarf). So, multiplying its rate of mass loss due to fusion by this, we get that the Sun in its current form will lose about 0.0338% of its mass due to fusion.

 

 

No.

 

Because the Sun’s outer layers vary in thickness, color, and luminosity from day to day, combined with its slow rate rate of evolution, and the very short (by astronomical standards) length of time which we’ve had precise instruments to watch it, we’ve not been able to directly observe its long-term evolution. It’s hard to precisely measure the diameter of a giant ball of magnetically whipped plasma. :)

 

Theoretical models of the Sun’s evolution tell us it will grow brighter and slightly larger for the next 5 billion year, but given its “noisiness”, many centuries of precise measurement will be needed to observationally confirm them. Most confirmation of these models comes from observing other stars which appear to be similar except for their age.

 

Thanks Craig - I appreciate your kind reply. As always, you attempt to supply hard facts in order to combat vague speculation!

 

Even so, one can't help feeling that there's something inherently incredible about the Sun. There it is, shining constantly, showing no evidence of change. Apart from transient sunspots, brief flickers of solar flares, and so on. But basically, it keeps on pumping out prodigious quantities of heat and light every day - while retaining its same undiminished self - shining serenely on, century after century, millenium after millenium.

 

As you say in your post, we can't directly observe or measure any changes in it. And it's this constancy which seems disturbing, as the OP implied.

 

Don't all other stars (supposing them to be suns) show evidence of change. Eg, they wax and wane in magnitude, as in variable stars. Or they erupt into novae, explode into supernovae, swell up and become Red Giants, or contract into White Dwarfs or Neutron Stars - even into the fabled Black Holes. The point is - they exhibit change.

 

Are we absolutely sure that our apparently unchanging Sun isn't some kind of special case. Possibly supernatural in origin?

[Village Idiot]

 

 

No scientific theory, mathematical proof, or evidence of which I’m aware suggest that matter in stars, or any other plasma, segregates itself by charge, electrons on the outside, protons on the inside (rather like a gigantic atom).

 

Heedless, if you know of some source supporting you claim otherwise, please post links or references to them. If you don’t, don’t make such claims!

 

I do not say that plasma segregates itself by charge. When an electric field exists, such as the downward-pointing field found on Earth http://hypertextbook.com/facts/1998/TreshaEdwards.shtml, then any positive charges are pushed downward, and hence, negative charges rise.

 

If an isolated spherical host were to hold a positive charge, a shell of protons would, according to the shell theorem as extended by Michael Faraday, present a positive charge as from the center of the host. The array of electrical charges would not be of the unconditional polarities you suggest that I have stated.

 

I have presented a logical conclusion to be drawn from well-known implications of the shell theorem. My only folly was to presume that this site would tolerate groundbreaking truth that has not yet come to light. An author of such a revelation could hardly be expected to find pre-existing support.

 

EDIT: Perhaps I misunderstand your instructions to supply supporting references. There must be such a thing as a prime source for a logical conclusion. To support an original conclusion, I could provide a supporting reference for the premise leading to that conclusion. A discovery can hardly be part of an existing consensus. Hence, consensus cannot lead to the founding of a discovery.

 

If a shell bearing electrical charge (an excess of a given polarity)contains similar additional shells within all the way down toward a central location, then there would always be some intensity of the central remaining until such content were nullified. Electrostatics assures no such internal charge, but the sustained dynamics of emerging charged particles of the outer shell's polarity would seem to fill the bill. Whether or not it has ever been said before, the thinking process leads me to believe that a rising host of electrons should be found if a core of protons were bringing positive charges to destruction where no electrons could be sharing their fate.

 

Intuitively, with no premise except for an excess of electrons upon a celestial sphere, is there any question as to what direction a free internal positive charge would go other than toward the center as the direction of the greater count of electrons lying beyond?

My existing reference to Faraday's electric field confirms the notion.

Edited January 17, 2013 by Heedless

[CraigD]

Don't all other stars (supposing them to be suns) show evidence of change. Eg, they wax and wane in magnitude, as in variable stars.

No – as best we can tell with current astronomy.

 

Not all stars have large short period variations in radiance.

 

The Sun’s radiance varies predominantly by about 0.1% with period 8 to 11 years. There’s believed to be a longer cycle, about varying by about 0.5% with period about 210 years. As light absorption and reflection by the Earth’s atmosphere can’t be accounted for with this precision, the ability to measure the Sun and other stars’ variance precisely has only existed for a few decades, via space-based instruments, though it’s possible to use data like centuries of sunspot counts and radioisotopes to estimate solar variance for the past few hundred years.

 

Long-term, theory gives that the Sun and similar stars long-term variance varies by much greater magnitudes. Theory gives that was only about 75% of its current brightness around 3,000,000,000 years ago. Because many complicated factors, primarily due to its atmosphere, effect conditions on Earth, however, it’s not possible to validate theory with geological evidence. The lack of obvious evidence supporting Solar evolution theory due to clear geological evidence that the Earth had liquid water 3,000,000,000 years ago is known as the faint young Sun paradox. The same theory predicts that the Sun will be about 40% brighter 4,000,000,000 years from now, before it leaves the stellar main sequence.

 

Because they are much further away from our instruments than the Sun, the precision of measuring variation in other stars isn’t as good as with the Sun, only about 3%. However, with the precision with which we can measure it, several “solar twin” stars have been identified with variance and other characteristics nearly identical to the Sun.

 

Or they erupt into novae, explode into supernovae, swell up and become Red Giants, or contract into White Dwarfs or Neutron Stars - even into the fabled Black Holes. The point is - they exhibit change.

Theory predicts that the Sun will leave the main sequence, beginning to swell up into a red giant in about 5,400,000,000 years, become a full-blown (pun intended) red giant 1,100,000,000 years later. After some spectacular shrinking and swellings as a red giant, the Sun should shrink into a white dwarf about 400,000,000 years after that.

 

Because these changes are so slow, no human has ever seen a star swell into a red giant or shrink into a white dwarf, and unless humans someday live for hundreds of millions of years, no human ever will.

 

Are we absolutely sure that our apparently unchanging Sun isn't some kind of special case.

Absolutely sure, no. Reasonably, as much or more than with most of astrophysics, yes.

 

Possibly supernatural in origin?

As science has failed to ever detect anything commonly called supernatural, such as gods or ghosts, I'm nearly certain the Sun is not being regulated by such a thing.

 

Science requires that we always remain open to the possibility of future theory-contradicting observation, so skeptical scientists and non-scientists can never be absolutely sure of anything. Absolute certainty isn’t a scientific concept, so isn’t very useful in scientific discussions.

[Eclogite]

Are we absolutely sure that our apparently unchanging Sun isn't some kind of special case.

Absolutely sure, no. Reasonably, as much or more than with most of astrophysics, yes.

Ah, the frustration and wonder of science. According to William Borucki, Principal Investigator for the Kepler Space Telescope, interviewd by the BBC at the AAS meeting on January 7th, the Kepler mission has been extended by four years. Reason: most of the observed stars were showing a greater variability in luminosity than expected (and more than the sun). This meant the signal to noise ratio was poor - the signal being the dimming in output caused by planetary transit.

 

On this basis it appears that many stars are (slightly) more variable than the sun.