Sunlight takes millions of years to transfer through solar body ?

[skysurfer]

According to this

http://en.wikipedia.org/wiki/Solar_core#Energy_transfer

it takes 17000 to 50 million years for photons to transfer from the solar core to its surface ? I cannot really understand the reason.
This would mean when the fusion in the Sun stops (and thus the Sun dies) we won't notice it for a long, long time.
I thought it takes slightly more than 2 seconds (solar radius = 696000 km)....

Any ideas on this ?

[gregbradley]

How could that possibly be worked out? I mean how could anyone measure or know how long it takes for a photon to go from the Sun's core to the surface?

Greg.

[mithrandir (Andrew)]

The photons are originally created as gamma rays in fusion reactions. These photons are repeatedly absorbed and re-emitted in random directions by atoms. Eventually they work their way out to a level in the sun where they can escape. The time averages out to millions of years.

When the sun runs out of fuel it will become a white dwarf. The universe has not existed long enough for the earliest white dwarfs to have cooled to black. They are still sitting there radiating their residual heat, and will be for billions if not trillions of years.

[Adelastro1 (Wayne England)]

In regard to the speed of light (or EM radiation), that is always quoted, is for a vacuum and that the speed of light in another medium is slower, ie. refractive index in glass etc (it's 200k km/h in glass, so ref index is 1.5). Assuming that radiation can pass through it, the speed depends on the medium's density and therefore for an extremely dense medium such as the Sun the speed will be very slow. But that assumes the photons don't interact catastrophically with the atoms in the dense plasma before they get to the surface. The article says: "The high-energy photons... take a long time to reach the Sun's surface, slowed down by the indirect path taken, as well as by constant absorption and reemission at lower energies in the solar mantle." Which means they continually interact with atoms and after one interaction may be emitted at an angle back where it came from for instance.

It goes on to say:
" The long periods of time (tens of millions of years) refer to the characteristic time for the entire solar temperature distribution to change, as a result of changing heat generation rate in the core. This is far longer than the average time for transport of heat through the Sun because most of the Sun's heat capacity is in the kinetic energy of the particles in its plasma, not in the electromagnetic radiation present within it. The shorter estimates of photon travel time (tens of thousands of years) refer to the relatively rapid mean time needed for radiation to travel from the center of the Sun to the photosphere, even though the Sun's heat cannot pass from core to surface at this rate, due to the large heat capacity needed to be heated or cooled in the process, as mentioned above."
So that's about thermal transfer....

This is just a brief article in Wiki so google some Physics texts for more info!

[Adelastro1 (Wayne England)]

Yeh what Andrew said!

[overlord (Charles)]

It's all theoretical.

It just means the swirly stuff is so swirly that the energy spiral is a million years long.... but in ten years they will totally reverse everything and say the opposite as they always do so I woudln't give it too much concern, particularly as the corona is actually the hottest part of the sun, not the inside. Read up on electric universe to blow your mind.

[Robh (Rob)]

Originally Posted by overlord

It's all theoretical.

It just means the swirly stuff is so swirly that the energy spiral is a million years long.... but in ten years they will totally reverse everything and say the opposite as they always do so I woudln't give it too much concern, particularly as the corona is actually the hottest part of the sun, not the inside. Read up on electric universe to blow your mind.

Some of it is is based on theoretical assumptions. Obviously, one cannot take a voyage to the centre of the Sun to get empirical evidence. There is, however a lot of observational evidence on stars and experimental evidence for the way nuclear reactions work. We are often too quick to trivialise existing scientific theory that has been developed and scrutinised by many brilliant scientists over many years.

It is important to note that a photon travels essentially unhindered in space at the speed of light. The photon that started out is the same photon at the end of its journey. However, in the Sun, the photon that emerges from the Sun is not the same one that started out in its core. Photons cannot travel unhindered in the Sun. They are absorbed and re-emitted many many times. This is essentially an energy transfer. As mithrandir stated, re-emitted photons travel in random directions. The calculation of time is based on "random-walk" mathematics given known and estimated parameters in nuclear fusion reactions.

The average temperature at the surface (photosphere) of the Sun is about 5,800 Kelvin. The corona is much hotter than the surface with temperature to 3 million Kelvin. The core is the hottest part of the Sun at about 15,000,000 Kelvin. The reason nuclear fusion occurs in the core is because of its high temperature.

Regards, Rob

[Raybot (Ray) (Ray)]

So it's like shoe-shopping with my wife:
The 'light' of my life races around inside the shopping centre, backwards and forwards, often returning to places she has already visited. Takes an age to come out, and then it's with a pair she didn't start with

[gregbradley]

Interesting discussion.

Regarding the core of the sun, is there data about what it consists of, how dense is the material?

I read somewhere the sun may have a metal core. Is that right? I thought metals were high up on the table of elements and would not sustain fusion easily.

My understanding of stars is that elemental hydrogen is the most abundant element. That it forms in clumps and accumulates together through gravity. With gravity and more material it forms pressure. With pressure comes heat. When enough of the hydrogen is dense enough the pressure forms enough heat to initiate fusion of the elemental hydrogen up the table of elements. Obviously then higher forms of elements do not require all the energy binding lesser elements and the left over is what the fusion reaction releases as heat and radiation.

I wonder how dense the core is and how much mass it has to have to start that reaction. Also even elemental hydrogen under that much pressure - is it still a gas or is it a semi or actual solid at that point?

Greg.

[Baddad (Marty)]

Amongst people who know better than I its generally accepted that photons can take millions of years to emerge from the core.

That analogy by Ray, Re: Wife shopping. That is great.
It does not mean every photon will take that long.
Something similar may occur with water on Earth. A molecule of water may take millions of years to cycle from the ocean to rain on land, absorbed by plants, into the stomach of a cow. eventually returning to the ocean and continuing into the next cycle.

Regarding the core. As the sun or star ages it changes from hydrogen to helium, progressing to carbon to oxygen. Iron in the later stages and depending on the star size it affects the stability.

Heavier elements develope in larger stars and it takes a super nova to generate gold, silver, uranium etc.

Its much more complex than that but will suffice as a simple explanation. However if iron is generated the star becomes unstable.

Cheers

[sjastro]

First of all the Electric Sun "model" is in the same boat as other classics such as the flat Earth theory and geocentric theory of the Universe.
It is pure bunkum that states that a gigantic electrical current emanating from our galaxy is accelerated towards the Sun and collides with particles in the Solar corona resulting in the high corona temperatures that are observed.
Apart from the the solar corona temperature it fails to explain any other phenomena associated with our Sun.

Here are three reasons why the model fails miserably and is by no means exhaustive.

(1) The surface of our Sun is composed of faculae or solar granules due to convection. Convection is caused by plasma heated in a much hotter interior, rising to the surface, cooling and falling back into the interior. These structures cannot exist if the primary heating source is the corona as the surface is now hotter than the interior and convection will occur in the opposite direction.
(2) The model states that the Sun is an anode and the surrounding heliosphere is a cathode. The potential difference between the electrodes drives the Birkeland current to the Sun. As anyone with a basic knowledge of physics would note the potential difference will drive positively and negatively charged particles in opposite directions. Yet the solar wind which is composed of both positively and negatively charged particles are moving in the same (outward) direction.
(3) The model also states that a double layer or charge separation occurs at the solar corona boundary. This accelerates the Birkeland current to near the speed of light which collides with the outer moving solar particles. This results in the heating of the corona.
The model doesn't explain why the double layer is formed at the corona.
What completely destroys this mechanism however is that particles travelling at near the speed of light and colliding would cause the emission of x-rays and gamma radiation. Thank goodness this doesn't occur as we would not be around to observe the display.

Equally nonsensical are models that claim that the Sun is composed of a metal core such as iron. Say your prayers if our Sun had an iron core as iron nuclei cannot sustain the fusion process as there is no excess energy to counter gravitational collapse of the core. The end result would be a nasty supernova explosion.
Besides spectroscopic analysis of the Sun only reveals trace amounts of iron at around 0.2%.

Finally the photons we observe are formed mainly in the outer layer due to interactions between charged particles and is a blackbody radiation rather than originating from the core from fusion.

Regards

Steven

[mithrandir (Andrew)]

Originally Posted by gregbradley

I read somewhere the sun may have a metal core. Is that right? I thought metals were high up on the table of elements and would not sustain fusion easily.

Greg, astrophysics considers everything above Helium to be a metal. All elements up to but not including Iron release energy in fusion. The Sun is not big enough to fuse anything above about Oxygen,and even that won't happen in any significant amount for a few billion years.

[Zhou (Mick)]

I will go off on a little bit of a tangent here:

When you are looking at a distant object through a telescope you are not actually viewing the photons from that object. If a photon is lucky enough to make it through our atmosphere unimpeded it will hit the objective lens (or primary mirror) of the telescope. It will then be absorbed by an atom within the lens and another one will be re-emmitted, this constant absorb-emit of photons within a substance is why light appears to travel slower through transparent objects compared to a vacuum. The same process will happen countless times in the eyepiece of your telescope and then your eyes. Finally what you end up seeing is photons emitted from from the atoms that the vitreous humour in your eyes are composed of. The same thing happens when photons are making there way from the centre of the sun to the its surface.