Galaxies - spiral arms split, why?

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    Galaxies Spiral Split
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Discussion Overview

The discussion revolves around the phenomenon of spiral arms in galaxies, specifically addressing why these arms appear to split or bifurcate. Participants explore various theories and observations related to the formation and structure of spiral galaxies, touching on gravitational influences, star formation, and observational effects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the splitting of spiral arms is due to previous mergers or some current influences.
  • Another participant highlights the complexity of understanding spiral structures, noting that simplistic analyses suggest tightly wound arms, which contradicts observations.
  • A participant observes that the branching of spiral arms appears peculiar when considering only gravity and mass.
  • One contribution references a documentary explaining that variations in gravity lead to closer interactions among objects, with the gravity field rotating around the center of the galaxy.
  • Another participant suggests that spiral arms are illusions created by regions of higher star formation, which are more visible due to the presence of blue stars, while areas between the arms contain similar amounts of material that are less visible.
  • A participant expresses understanding of the arms as areas of condensation and uniform material, while questioning the movement of stars in relation to the rotating gravity field.
  • Another participant provides an estimate of the solar system's orbital period around the galaxy, suggesting it is about 250 million years.

Areas of Agreement / Disagreement

Participants express a range of views on the nature of spiral arms, with no consensus reached on the exact mechanisms behind their splitting or the implications of gravitational interactions. The discussion remains unresolved with multiple competing theories presented.

Contextual Notes

Some claims rely on observational interpretations and may depend on specific definitions of terms like "split" and "gravity field." The discussion includes assumptions about the nature of star formation and the visibility of materials in galaxies.

precisionart
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Why do the spiral arms of galaxies split or bifurcate? Is this due to a previous merger or some kind of current?
 
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Can you be more specific? What do you mean by "split"?

As it turns out, understanding why galaxies have the spiral structures they do is a complicated question. A simplistic analysis says that all galaxies should have their spiral arms tightly wound up, but this is manifestly not the case. See the Wikipedia http://en.wikipedia.org/wiki/Spiral_galaxy#Origin_of_the_spiral_structure" for further discussion.
 
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If you observe some of the better shots of the spiral galaxies, each arm branches in a very peculiar way. It does not make sense to me given only gravity and mass.
 
I saw a documentry that explained it quite well, they talked about slight variations in gravity, causing object to come closer together, to be even more attacked by each other.

They also showed that the objects themselves remain stationary, and the gravity field rotates around the centre.
 
Also spiral arms are something of an illusion. What happens is that spiral arms are places where there are more star formation, and areas with more star formation have lots of blue stars. So when you take a picture with instruments that are particularly sensitive to blue light, you see lots of blue stars in the arms.

In fact it's not true that there is "nothing" between the arms. It turns out that with current models of galactic structure that the areas between the arms have as nearly as much "stuff" as the arms. It's just that the "stuff" between the arms are dark bits of gas and dust that don't show up in picture.
 
Ok, I understand that the arms are areas of a type of condensation and that material is more uniform.

Darryl,
You mentioned that the objects (stars?) don't move but that the gravity field rotates instead. I thought I once heard about the orbit time or our star around the galaxy (60 mill years?) so is this true?

Also, the split arms would indicate a kind of offset gravity interference. I also notice strange concentric circles around supernovae.

Anyways, I appreciate the responses and this cool forum. Thanks.
 
i believe the orbit time for our solar system to make one revolution is about 250 million years
 

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