Nebular Theory: Understanding Flattening Process

[Trinitiet]

Hi,

I try to understand the nebular theory (how the solar systems are formed) but I keep having problems with the flattening.

My physical intuition "feels" the flattening process should happen, but I want a physical/mathematical qualitative explanation.

What is the key physical law that makes the flattening happen?

Thanks!

Trinitiet.

 

[Chalnoth]

Hi,

I try to understand the nebular theory (how the solar systems are formed) but I keep having problems with the flattening.

My physical intuition "feels" the flattening process should happen, but I want a physical/mathematical qualitative explanation.

What is the key physical law that makes the flattening happen?

Thanks!

Trinitiet.

It's basically just friction.

Consider that simply by random chance, the cloud of gas will have some net angular momentum. Friction sort of averages out this angular momentum between the particles, and any particles with orbit not in the plane of rotation quickly, through friction, move to orbits within the plane of rotation.

 

[Trinitiet]

It's basically just friction.

Consider that simply by random chance, the cloud of gas will have some net angular momentum. Friction sort of averages out this angular momentum between the particles, and any particles with orbit not in the plane of rotation quickly, through friction, move to orbits within the plane of rotation.

Thanks :-)
Is gravity the force that leads it there to?

 

[Chalnoth]

Thanks :-)
Is gravity the force that leads it there to?

Well, gravity has an impact, but isn't the main reason. Once the cloud is self-gravitating, with all of its particles in mutual orbits around one another, the reason why those particles go into lower orbits over time is due to this friction (as well as simple thermal emission of photons), which is primarily an electromagnetic phenomenon.

 

[Trinitiet]

Well, gravity has an impact, but isn't the main reason. Once the cloud is self-gravitating, with all of its particles in mutual orbits around one another, the reason why those particles go into lower orbits over time is due to this friction (as well as simple thermal emission of photons), which is primarily an electromagnetic phenomenon.

As friction takes place, only in the direction the particle moves, wouldn't then friction only make the particle rotate slower (thus making each rotating circle of particles smaller), rather than moving the particles to one common plane?

 

[Chalnoth]

As friction takes place, only in the direction the particle moves, wouldn't then friction only make the particle rotate slower (thus making each rotating circle of particles smaller), rather than moving the particles to one common plane?

In a microscopic view, the friction is a result of random interactions such as atom-atom collisions. So no, the friction doesn't just make them slower, it tends to change their direction randomly. Such collisions, however, tend to release some of their energy in the form of radiation, which means that there is less energy in the system, which means they are forced to take lower orbits.

But those particles that manage to find themselves in a common plane of rotation experience less friction, and so fall to the center of the gravitational potential well more slowly.

 

[Trinitiet]

In a microscopic view, the friction is a result of random interactions such as atom-atom collisions. So no, the friction doesn't just make them slower, it tends to change their direction randomly. But those particles that manage to find themselves in a common plane of rotation experience less friction, and so fall to the center of the gravitational potential well more slowly.

Ah thanks :-) !