Why are our planets and galaxy in a plane shape?

Click For Summary

Discussion Overview

The discussion centers on the arrangement of planets in the solar system and the structure of galaxies, specifically why they tend to form in a planar shape rather than a random distribution. The scope includes theoretical explanations related to astrophysics and the dynamics of rotating masses.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • Some participants propose that a disk shape is the most 'economical' for conserving angular momentum in a rotating mass, as noted by Space Tiger.
  • Others mention that during the coalescence of an initial gas cloud, it would naturally settle into a disk shape due to these dynamics.
  • A later reply highlights the incomplete understanding of real disk system formation, suggesting that minimum energy conditions play a role in this process.
  • It is noted that without angular momentum or with collisionless particles, a spherical shape would be expected, while heavily interacting particles with significant angular momentum tend to form disks.

Areas of Agreement / Disagreement

Participants generally agree on the role of angular momentum in the formation of disk shapes, but the discussion acknowledges that there is still no complete understanding of the formation processes involved.

Contextual Notes

Limitations include the dependence on definitions of angular momentum and energy conditions, as well as unresolved aspects of the formation of disk systems.

syano
Messages
82
Reaction score
0
Why are the planets in our solar system spread out in a plane instead of being more randomly spread around the Sun? And why is our galaxy in the shape of a plane instead of all the stars in our galaxy being more randomly spread around the middle of our galaxy?

Thanks,
 
Astronomy news on Phys.org
As Space Tiger explained in a different thread, a disk is the most 'economical' shape for conservation of angular momentum in a rotating mass. When the initial gas cloud was coalescing, therefore, it would naturally settle in that way.
 
Here's the thread:

https://www.physicsforums.com/showthread.php?t=93098&highlight=disk"

Keep in mind that we still don't have a complete understanding of the formation of real disk systems, but it's best just to think of these as "minimum energy conditions". With no angular momentum or with collisionless particles, you will tend to get a sphere. With heavily interacting particles that have a lot of angular momentum, you tend to get disks.
 
Last edited by a moderator:
Thanks yet again, Mr. Tiger, for setting things straight. While astrophysics is one of my favourite things in life, I really have no education at all in it. It's always a pleasure to read your posts and further my knowledge. Cheers, bud.
edit: So what happened to my edit in the previous post where I said that ST's explanation was better?
 
Last edited:

Similar threads

  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 36 ·
2
Replies
36
Views
7K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 22 ·
Replies
22
Views
4K