Can anything fall into the Sun?

[Mordred]

Here is an examination for you key note the line under the Poynting Robertson effect.

 

 

 

"the absorption of this radiation leads to a force with a component against the direction of movement. (The angle of aberration is extremely small since the radiation is moving at the speed of light while the dust grain is moving many orders of magnitude slower than that.) The result is a slow spiral of dust grains into the Sun. Over long periods of time this effect cleans out much of the dust in the Solar System"

 

 

http://en.m.wikipedia.org/wiki/Radiation_pressure

 

http://en.m.wikipedia.org/wiki/Poynting%E2%80%93Robertson_effect

 

Here is an examination on fluffy particles. This article specifically calculates the lifetimes of particles.

 

Key note they still fall into the sun eventually....

 

"Because fluffy grains rotating rapidly in random orientations

are weakly perturbed by the nonradial radiation pressure, the

equation of motion assuming β2 = β3 = 0 can reasonably well

describe their trajectories. As a result, the rapidly and randomly

rotating grains spiral into the Sun due to the PoyntingRobertson

effect even though they are fluffy aggregates. "

 

http://astro.berkeley.edu/~kalas/disksite/library/kimura02a.pdf

 

 

The last link has the relevant equations.

 

 

(By the way the question is a good one, as it leads to a greater understanding of solar system dynamics. Radiation pressure vs gravity)

 

Also note the Poynting Robertson effect is smaller particles ie the comet trail or exploded comet material.

 

Larger grains also fall into the sun as the radiation pressure is negligible compared to the Suns gravity for larger bodies .

( unless that body has achieved escape velocity, but that also depends on trajectory as well as velocity)

Edited April 27, 2015 by Mordred

[swansont]

If they found granules embedded in the felled trees that would be pretty convincing evidence.

But I beg to differ as to whether the same would occur on the Sun.

On what scientific basis do you beg to differ?

 

Let's see a calculation that supports this "differing"? If you can't come up with anything, you have nothing on which to base this assertion.

[Robittybob1]

On what scientific basis do you beg to differ?

 

Let's see a calculation that supports this "differing"? If you can't come up with anything, you have nothing on which to base this assertion.

Look at those video clips, there is a huge and rapid movement of mass away from the Sun associated with the comet impact.

The Poynting Robertson effect (PR) (inward) only deals with a particular sized particle and all other sizes are driven the other way (outward). It has really upset me and I am determined to look into it again.

Now seeing is scientific surely.

Even on the outward leg of a comet's journey the tails are pointing (predominantly) away from the Sun. Now you give me a scientific reason why the dust particles will at some stage change direction and go toward the Sun.

My "beg to differ" was a challenge to the poster's (pavelcherepan) opinion. He expressed an opinion and I begged to differ.

(What was that negative score for?)

Edited April 27, 2015 by Robittybob1

[Mordred]

May be outward initially but the Poynting Roberston metric applies to the entire solar system. Gradually it will cause sufficient change in momentum to clean up the dust.

 

You've already noticed this so the rest is more fyi of other readers

 

 

The reason for the change in momentum is simple. Gravity works it is a continuous force acting upon the dust. The only way it can escape is if it exceeds escape velocity.

The force of gravity also exceeds the radiation pressure so the net force is toward the sun

 

 

The last link covers the metrics study it in detail.

 

 

Look at the term radiation pressure.

 

Specifically the definion of pressure=force per unit area.

 

Solar sails work with a large surface area which provides more thrust due to more force.

 

Dust has a minute surface area so radiation pressure exerts negligible force upon dust. Gravity however is the same force regardless of surface area.

No idea on the negative score though I myself rarely give negative points.

Edited April 27, 2015 by Mordred

[Robittybob1]

May be outward initially but the Poynting Roberston metric applies to the entire solar system. Gradually it will cause sufficient change in momentum to clean up the dust. ....

I wonder if the solar radiation pressure will not always swamp out the PR effect. It has really got me baffled for I know about the aberration of light and how the apparent incident angle changes, so I don't have a problem with that, but what I couldn't understand was what was the interaction of the photon with the dust particle? Was it reflection or absorption?

The Sun is rotating WRT to the Solar System (the equatorial regions take about a month (26 days?) to transit the circumference of the Sun), so the radiation coming off the Sun should be blueshifted for the photons that come off in the direction of rotation and redshifted for the opposite direction, so any interaction with dust particles will reflect this imbalanced momentum.

Does the PR effect take that into account?

Edited April 27, 2015 by Robittybob1

[Mordred]

Redshift is a change in frequency not momentum. Momentum of photons is always c. The change in kinetic energy is a function of the temperature in the PR equations.

[swansont]

Look at those video clips, there is a huge and rapid movement of mass away from the Sun associated with the comet impact.

The Poynting Robertson effect (PR) (inward) only deals with a particular sized particle and all other sizes are driven the other way (outward). It has really upset me and I am determined to look into it again.

Now seeing is scientific surely.

 

Depends on whether it can count as a measurement. Quite often, seeing isn't scientific.

 

Even on the outward leg of a comet's journey the tails are pointing (predominantly) away from the Sun.

 

 

On the inward leg this is true as well, but the tail as a whole is still moving toward the sun. SO what you need to do is establish the particles of the tail are moving away from the sun.

 

Now you give me a scientific reason why the dust particles will at some stage change direction and go toward the Sun.

That's not a valid objection. The particles start out with the velocity of the comet itself. If radiation pressure was equal to gravity, the particle would still move away from the sun.

 

My "beg to differ" was a challenge to the poster's (pavelcherepan) opinion. He expressed an opinion and I begged to differ.

Scientific opinion, at the very least. Still needs scientific justification. (and Mordred had already posted links, so you are contradicting a concept with scientific backing)

[Robittybob1]

Redshift is a change in frequency not momentum. Momentum of photons is always c. The change in kinetic energy is a function of the temperature in the PR equations.

OK if temperatures are involved the light energy must be absorbed rather than reflected.

 

I disagree about your momentum statement. Momentum of a photon is proportional to its frequency. http://en.wikipedia.org/wiki/Photon

 

 

In empty space, the photon moves at c (the speed of light) and its energy and momentum are related by E = pc, where p is the magnitude of the momentum vector p. This derives from the following relativistic relation, with m = 0:[14]

E^{2}=p^{2} c^{2} + m^{2} c^{4}.

The energy and momentum of a photon depend only on its frequency (ν) or inversely, its wavelength (λ):

Its velocity is always c but when emitted from a moving source the moving source will increase the photon's frequency.

Edited April 27, 2015 by Robittybob1

[swansont]

Redshift is a change in frequency not momentum. Momentum of photons is always c. The change in kinetic energy is a function of the temperature in the PR equations.

Momentum of photons is E/c

[Robittybob1]

 

Depends on whether it can count as a measurement. Quite often, seeing isn't scientific.

 

 

 

On the inward leg this is true as well, but the tail as a whole is still moving toward the sun. SO what you need to do is establish the particles of the tail are moving away from the sun.

 

That's not a valid objection. The particles start out with the velocity of the comet itself. If radiation pressure was equal to gravity, the particle would still move away from the sun.

 

Scientific opinion, at the very least. Still needs scientific justification. (and Mordred had already posted links, so you are contradicting a concept with scientific backing)

We see the comet fall towards the Sun and then we see this plume of matter being ejected from the Sun.

Both aspects are seen and I believe they are causaully related.

 

 

Momentum of photons is E/c

Yes that's right, but do you agree the photons from the Sun will have different energy values depending on the direction of the emitting source?

Edited April 27, 2015 by Robittybob1

[swansont]

Say we have a material that has some density. Mass goes up with r^3, but surface area goes up with r^2. So as mass increases gravitational force increases faster than radiation pressure, meaning there is possibly some critical size where the net force changes direction.

 

Intensity of light and gravity both drop with r^2, so you should have no change in effect with distance.

 

If you read the link on the P-R effect, they have the equation, and the equation for the parameter. The dust particles that get blown out are smaller than a micron. Larger ones don't.

 

Yes that's right, but do you agree the photons from the Sun will have different energy values depending on the direction of the emitting source?

 

I don't see how this is a consideration, but I think the sun can only be moving in one direction, so there is no "direction of the emitting source" to worry about. In the sun's frame, the radiation on average is directed radially outward.

 

Radiation pressure only depends on the radiated power, not the individual wavelengths.

[Robittybob1]

Say we have a material that has some density. Mass goes up with r^3, but surface area goes up with r^2. So as mass increases gravitational force increases faster than radiation pressure, meaning there is possibly some critical size where the net force changes direction.

 

Intensity of light and gravity both drop with r^2, so you should have no change in effect with distance.

 

If you read the link on the P-R effect, they have the equation, and the equation for the parameter. The dust particles that get blown out are smaller than a micron. Larger ones don't.

 

I don't see how this is a consideration, but I think the sun can only be moving in one direction, so there is no "direction of the emitting source" to worry about. In the sun's frame, the radiation on average is directed radially outward.

 

Radiation pressure only depends on the radiated power, not the individual wavelengths.

That was a helpful answer. I can see where you are coming from regarding the size of the particles.

The direction of the emitting source on average might be "radially outward", but as the Sun rotates on it axis from the West to the East, as does the Earth, photons from the west (side going toward any dust particles) will have a slightly higher frequency than the ones coming from the Eastern side (side going away from dust particles). If this is correct the radiant pressure should promote dust in its orbital path.

Radiant power must be the summation of the power in all the individual photons and their wavelengths.

Edited April 27, 2015 by Robittybob1

[swansont]

 

 

The direction of the emitting source on average might be "radially outward", but as the Sun rotates on it axis from the West to the East, as does the Earth, photons from the west (side going toward any dust particles) will have a slightly higher frequency than the ones coming from the Eastern side (side going away from dust particles). If this is correct the radiant pressure should promote dust in its orbital path.

 

Yes, key word is slightly. How big of an energy shift would this cause? Do we even notice a bluing vs reddening of the light, if this were present at the level of even a few percent of the energy of visible light?

[Robittybob1]

 

 

Yes, key word is slightly. How big of an energy shift would this cause? Do we even notice a bluing vs reddening of the light, if this were present at the level of even a few percent of the energy of visible light?

It could be greater than the PR effect. This is such a detailed discussion and I need some time to look into it. I'm at work and I have other things to do but I'll research it later and get back to you.

 

One thing I feel certain about is that the orbital motion of the dust is what overcomes the force of gravity, so then it is a matter of what additional effects upset this balance.

1. Slowing due to the PR effect

2. Promotion due to this other Blueshift effect

3. Radiant pressure

4. Solar wind

Edited April 27, 2015 by Robittybob1

[Robittybob1]

It could be greater than the PR effect. This is such a detailed discussion and I need some time to look into it. I'm at work and I have other things to do but I'll research it later and get back to you.

 

One thing I feel certain about is that the orbital motion of the dust is what overcomes the force of gravity, so then it is a matter of what additional effects upset this balance.

1. Slowing due to the PR effect

2. Promotion due to this other Blueshift effect

3. Radiant pressure

4. Solar wind

Trying to get some basic understanding of these 4 things and came across this YT introduction to the Solar Wind

"Solar Wind Introduction | Sun Series 1" It is only a couple of minutes long but it will make you think. Why does the Solar Wind contain all the known elements ( I could only imagine those comets being blasted back into space in the form of molecules. Sorry about that.) How come the Solar Wind is not affected by the gravitation of the Sun? I've asked this question before (another forum) and never got an answer.

This section from Wikipedia covers it a bit but maybe it isn't known yet. http://en.wikipedia.org/wiki/Solar_wind#Emission

 

The Solar wind particles seems to be able to be accelerated beyond the escape velocity of the Sun, (solar escape velocity of 618 km/s).

Radiant Pressure: http://en.wikipedia.org/wiki/Radiation_pressure

 

The radiation pressure results in forces and torques on the bodies that can change their translational and rotational motions. Translational changes affect the orbits of the bodies. Rotational rates may increase or decrease. Loosely aggregated bodies may break apart under high rotation rates. Dust grains can either leave the Solar System or spiral into the Sun.

Either way! "Spiral into the Sun" is obviously a reference to the P-R effect.

 

 

If the P-R effect was really significant there would be no clearing of the inner Solar system while there is still major dust further out!

 

 

Stellar planetary systems[edit]

A protoplanetary disk with a cleared central region. http://en.wikipedia.org/wiki/Radiation_pressure#/media/File:David_A._Aguilar%27s_Red_Dwarf_Stars.jpg Artist's impression!

Planetary systems are generally believed to form as part of the same process that results in star formation. A protoplanetary disk forms by gravitational collapse of a molecular cloud, called a solar nebula, and then evolves into a planetary system by collisions and gravitational capture. Radiation pressure can clear a region in the immediate vicinity of the star. As the formation process continues, radiation pressure continues to play a role in affecting the distribution of matter. In particular, dust and grains can spiral into the star or escape the stellar system under the action of radiation pressure.

Well that's what I think at this stage but still researching.

That looks like radiant pressure is the dominant effect over all.

Edited April 28, 2015 by Robittybob1

[Mordred]

Ok now we're define definetely hitting a tricky subject matter. Unfortunately there is no truly easy way to explain solar winds. First we need to decide it into two categories.

 

Fast solar winds and slow solar winds. (Highly important as it involves different processes, as well as source)

 

Now one thing to realize is what particles are affected by solar winds? We decide this into two groups ions and electrons. (Charged particles). Those charged particles are accelerated via magnetic convection in the fast solar wind this convection is generated by coronal holes. But only charged particles with the right momentum to start with are accelerated. Charged particles slightly slower than the magnetic wave phase velocity are accelerated, particles faster than the magnetic wave phase velocity is decelerated. Those charged particles must resonate with the magnetic wave phase velocity to become solar wind particles. Best analogy think of how a surfer must match speeds with a wave of water. Same principle Google Landau damping for further details.

 

http://en.m.wikipedia.org/wiki/Landau_damping

 

 

Now particles that do resonate behave differently ions will rotate with a left handedness electrons with a right handedness. ( visualize a spring turn that spring left (left handedness, or right Right handedness.

 

(Gyromagnetic ratio)

http://en.m.wikipedia.org/wiki/Gyromagnetic_ratio

 

 

here is a detailed article on solar winds. It's rather involved and I certainly didn't paint the full picture...... nor can I in one post without wrting a book. Lol

 

http://www.ieap.uni-kiel.de/et/people/wimmer/teaching/et2/et2.pdf

It's been awhile since I last read the last paper, I pulled it from my drop box archives

(If I recall it correctly there is a section on Poynting Robertson as well as the effects of redshift)

[Robittybob1]

Ok now we're define definetely hitting a tricky subject matter. Unfortunately there is no truly easy way to explain solar winds. First we need to decide it into two categories.

 

......

 

(Gyromagnetic ratio)

http://en.m.wikipedia.org/wiki/Gyromagnetic_ratio

 

 

here is a detailed article on solar winds. It's rather involved and I certainly didn't paint the full picture...... nor can I in one post without wrting a book. Lol

 

http://www.ieap.uni-kiel.de/et/people/wimmer/teaching/et2/et2.pdf

It's been awhile since I last read the last paper, I pulled it from my drop box archives

(If I recall it correctly there is a section on Poynting Robertson as well as the effects of redshift)

That was a book; 242 pages of difficult maths!

Edited April 28, 2015 by Robittybob1

[Mordred]

Lol true, however it is in a textbook style with excellent supporting descriptives, as well as good visuals aids. All things considering it is an excellent coverage of the solar winds in all its dynamics.

My advise read through it, use it as a reference aid to ask questions regarding the material. If you start a new thread on those questions. Post the article then refer to the section.

 

 

In all honesty that's the best way to truly learn on forums. Find a reference article, post that article and ask questions on specific sections.

(Your more likely to avoid drawing false conclusions by doing so. It's a method that served me well when I first started studying physics)

Just make sure the material isn't copyright

[Robittybob1]

Lol true, however it is in a textbook style with excellent supporting descriptives, as well as good visuals aids. All things considering it is an excellent coverage of the solar winds in all its dynamics.

My advise read through it, use it as a reference aid to ask questions regarding the material. If you start a new thread on those questions. Post the article then refer to the section.

 

 

In all honesty that's the best way to truly learn on forums. Find a reference article, post that article and ask questions on specific sections.

(Your more likely to avoid drawing false conclusions by doing so. It's a method that served me well when I first started studying physics)

Just make sure the material isn't copyright

Yes it is rather good reading. I read a bit about sputtering and loss of mass of a dust particle as it spiraled in from 2 AU to 1 AU. Home time.

[Robittybob1]

Has anyone seen actual evidence of the Poynting - Robertson effect? I know there is a mathematical argument that light (EM radiation from the Sun) will slow small particulate matter but is there physical evidence for it?

 

If there are 3 or 4 other reasons for clearing the Solar System of dust why is the Poynting - Robertson effect raved about so much, when it is the only one that brings the dust spiraling inward when all the others have the dust being blown outward, and all the Hubble photos and other images support the dust being blown outward rather than inward?

Edited April 28, 2015 by Robittybob1

[Mordred]

Think of it in terms of thermodynamics.

 

Heat one side of a particle that heat radiates from the particle itself.

 

A good example is using a laser to move an asteroid trajectory. This effect combined with gravity and radiation pressure causes the curved orbital. The radiating heat assists in degradation of the particles orbit.

 

 

Basically because the dust is reradiating heat, it slows down. When you slow down an orbitting body you change its orbit.

Poynting vector is simply one of the more well known methods of clearing dust. The solar winds only affect a small % of the infalling particles and only charged particles of small size

Edited April 28, 2015 by Mordred

[Robittybob1]

Think of it in terms of thermodynamics.

 

Heat one side of a particle that heat radiates from the particle itself.

 

A good example is using a laser to move an asteroid trajectory. This effect combined with gravity and radiation pressure causes the curved orbital. The radiating heat assists in degradation of the particles orbit.

 

Poynting vector is simply one of the more well known methods of clearing dust. The solar winds only affect a small % of the infalling particles and only charged particles of small size

As I understand it, heat is absorbed from the Sun but since the particle is moving the apparent angle of the incident light is slightly ahead from being absolutely radial (aberration of light), and since the radiation of that heat will be isotropic (I understand that to be evenly all round the particle) the net effect is a reduction in the momentum, and subsequent infalling of the particle.

There seems to be at least 2 parts missing:

1.. The effect of the impact momentum. I have not seen any accounting for that.

2. Also it is rather a presumption to say that the particle heated from one side only will have a similar temperature throughout.

 

Well they are the points that have raised doubt in my mind, and so I'm looking into it.

Edited April 29, 2015 by Robittybob1

[Mordred]

( We see evidence that this basic principle works all the time, we know Heat, kinetic energy provides thrust)

As I understand it heat is absorbed from the Sun but since the particle is moving the apparent angle of the incident light is slightly ahead from being absolutely radial (aberration of light), and since the radiation of that heat will be isotropic (I understand that to be evenly all round the particle) the net effect is a reduction in the momentum, and subsequent infalling of the particle.

There seems to be at least 2 parts missing:

1.. The effect of the impact momentum. I have not seen any accounting for that.

2. Also it is rather a presumption to say that the particle heated from one side only will have a similar temperature throughout.

 

Well they are the points that have raised doubt in my mind, and so I'm looking into it.

Recall the size of the particles affected. Now let those particles tumble spin etc, can you say one side is consistently hotter than the other?

 

The rest of the above is accurate

Where would you define a point of impact in a gaseous body

[Robittybob1]

( We see evidence that this basic principle works all the time, we know Heat, kinetic energy provides thrust)

 

Recall the size of the particles affected. Now let those particles tumble spin etc, can you say one side is consistently hotter than the other?

 

The rest of the above is accurate

Where would you define a point of impact in a gaseous body

If they were spinning? What makes them spin? If the were spinning from the beginning they would tend to slow down (I've printed a study on the "spin-down of the Sun" so I suspect the same would be true for a particle, but if they were spinning (with the right axis of rotation) they would help to even out the temperature. Can an object have more than one axis of rotation?

[Mordred]

We're dealing with dust the size of sand on a beach, ever try heating one side and keeping the other side significantly cooler. Wouldn't take long for heat convection to balance the temperature.

 

Dust usually has some spin in space, minute variations in temperature, collisions with other particles impart spin. Follows the conservation of angular momentum just like any other object. I seriously doubt you would find a significant % of dust without some rotation.

 

Would actually be an extremely small %

Remember the size. 1 µm to 1 mm in diameter.= dust..or grains of sand if you prefer

The Poynting Robertson metric only affects this size range. However as this size range gradually conglomerates to larger rocks, such as the proto plasma disk, having a significant reduction of dust available prevents formation of larger bodies such as planets.

( This is where the debate on the lifetime of dust is so vital and highly contested.)