Thread: fusion stops in Sun. It expands cools and Earth gets... hotter?

Nobody said the core cools as it shrinks. You just made that up. The hydrogen fuel is exhausted, so gravitational collapse heats the core until helium fusion takes over. There is no helium or light element fusion going on right now because the sun's core is not hot enough.

Indeed, formation of a planetary nebula is very similar to a supernova. The difference is that in a supernova, the core collapses much more violently because it is heavier. Our sun is small, so it will fizzle instead of boom.

Originally Posted by Larry Caldwell

Nobody said the core cools as it shrinks. You just made that up.

I didn't make anything up. I asked a question about the physical mechanics of this "collapse" which you still haven't answered. Compression? Shrinkage? Disapearance into the 8th dimension?

We know why it's not shrinking now. It's hot. Hot enough to resist any further gravitational compression. So what physical change occurs to reduce the physical resistance to compression that the heat causes?

By the way a supernova is nothing like a planetary nebula any more than a beachball is like a gopher because they are made of the same things..

No. I am not a nuclear physicist.. nor are you, or you would not need to ask...

So any answer I provide is MY understanding which I shall be willing to share..

A rough understanding of what drives stars is at the core of this question..

I see it as this; Our Sun is a medium mid life star.. in its main sequence.

That it is at its core fusing hydrogen into helium. The fusion process.

A stable balance is observed between compression of mass by gravity force,

and the heat energy generated by that fusion proses..ongoing.

At the point where hydrogen available is converted and that balance becomes less stable..

As that fusion process lessens the gravity force increases pressures at the core.

That increased pressure allows the conversion of Helium into Iron. The red giant is born and begins..

The higher temperature at the core makes the star swell.

The inner planets might not be far enough away from the growing star to avoid being consumed..

Some billions of years later when the available helium has been spent..

The Sun will start to cool and shrink back into a white dwarf..

The mechanism of the collapse is gravity. You seem to be under the impression that the only reason the core is not collapsing now is heat. That is not true. The fusion process generates gamma rays, and photon pressure adds to the effect of the heat to keep the core from collapsing. It takes somewhere between 10,000 and 170,000 years for a photon to work its way from the core to the surface of the sun. The sun fuses about 4 million tons of hydrogen into helium every second, so you can see, that's a LOT of photons.

As a scientist you make a great lawyer. The physical world operates the same whether you understand it or not.

A photon is just a carrier of the heat energy. It goes from atom to atom via stimulation of electrons until it gets to the surface to escape as light. It is representative of heat. At that level it is the "heat". As the core loses photons it loses heat. If that energy isn't replaced by the stimulation of the electrons, which then produce photons, caused by fusion produced gamma rays, fast neutrons, alpha particles etc. slipping around into the surrounding atoms until they transfer their energy to the surrounding material in the form of stimulated electrons and photons then the core cools. It is the highly stimulated "hot" electrons in atoms which repel each other that is by far the dominant resistance to the gravitational compression.

Like I said, a great lawyer. You are ignoring the momentum of the photon, which is always conserved. The energy of a photon may be absorbed by pair production, but the resultant pair will carry the momentum of the photon unchanged. The core of the sun is already ionized, but the charge on the protons still neutralizes the charge on the electrons. There may be some slight gravitational separation of the heavier protons, but electromagnetic forces would easily overwhelm any gravitational effects. It's true that the sun is positively charged, but like any sphere, the charge separation concentrates at the surface of the sphere, not the core.

If you want to run with this electrostatic repulsion hypothesis, you need to come up with a reason that it quits working when hydrogen is exhausted, and doesn't start working again when the star switches to helium fusion.

Brownian motion.