Spiral Galaxies' Arms

  • #1
Sanborn Chase
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Why do the arms of spiral galaxies usually bifurcate? Is the visible matter in them moving in or out from the center?
 

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  • #2
Drakkith
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The visible matter is mostly moving in complicated elliptical orbits about the center of the galaxy, but I'm sure a small amount is sent towards or away from the center due to gravitational interactions. I can't answer why they are bifurcated though.
 
  • #3
davenn
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Why do the arms of spiral galaxies usually bifurcate? Is the visible matter in them moving in or out from the center?
2 armed galaxies are only one of many forms, many have multiple arms, many have none that can be easily identified
 
  • #4
One thing to keep in mind is that spiral arms in galaxies are "density waves" and not actual structures of the matter. They represent the area where many millions of stellar orbits reach their maximum distance from the galactic center of mass. At this point they are traveling the slowest and so "pile up" in the region producing the appearance of more stars than in-between the arms. But the individual stars in each arm are changing continuously.

Put another way, the arms are an illusion. They aren't like a whirlpool or anything like that.
 
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  • #5
davenn
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One thing to keep in mind is that spiral arms in galaxies are "density waves" and not actual structures of the matter. They represent the area where many millions of stellar orbits reach their maximum distance from the galactic center of mass. At this point they are traveling the slowest and so "pile up" in the region producing the appearance of more stars than in-between the arms. But the individual stars in each arm are changing continuously.

Put another way, the arms are an illusion. They aren't like a whirlpool or anything like that.

ohh yeah ???
I would like to see some valid citations for your comment !!

there is NO "appearance" they are really there you can see them go supernova, you can do spectroscopic work on those stars

Their location IS physical

Dave
 
  • #6
Sanborn Chase
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2 armed galaxies are only one of many forms, many have multiple arms, many have none that can be easily identified
 
  • #7
The stars are real but the arms in a spiral galaxy are not; as I stated, they are simply an illusion. I'd recommend An Introduction to Modern Astrophysics as a reference. It's in one of the later chapters if I recall correctly...

(Think of where an oscillating particle spends most of its time: on the edges of its motion. This is because it is traveling slowest at that point. It's the same thing with galaxies and stellar orbits. The stars just spend more time there.)
 
  • #8
Chronos
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The stars in a galaxy really are [were, given the finite speed of light] where they appear to be as Dave noted, however, Rex is correct in that they do not form and remain in spiral arms as they orbit a spiral galaxy. Their individual motions follow a density wave profile as illustrated here .
 
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  • #9
Sanborn Chase
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The stars in a galaxy really are [were, given the finite speed of light] where they appear to be as Dave noted, however, Rex is correct in that they do not form and remain in spiral arms as they orbit a spiral galaxy. Their individual motions follow a density wave profile as illustrated here .
First, thank you all for taking the time to answer my questions.
Chronos, the video clip of the motions of stars in a spiral galaxy was most illuminating and answered the second part of my first post concerning the movement of individual stars into and out of the center.
As the galaxy itself is moving through space(and time) would it not form the basic configuration of a transformer?
Again, many thanks to all of you.
 
  • #10
Excellent video!

Sanborn Chase, do you mean an electric transformer?
 
  • #11
Sanborn Chase
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Excellent video!

Sanborn Chase, do you mean an electric transformer?
Yes, an electrical type transformer in its form. And Mr. Bernhardt cautioned me about posting pet theories, personal opinions, etc. I trust I haven't bent the pipe.
 
  • #12
Drakkith
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As the galaxy itself is moving through space(and time) would it not form the basic configuration of a transformer?
No. Not at all.
 
  • #13
phinds
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Yes, an electrical type transformer in its form.
I'm curious what characteristic led you to that conclusion. I must be missing something because I just don't see it at all. I mean, I know that it's NOT, I'm just curious why you think it might be.
 
  • #14
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Why do the arms of spiral galaxies usually bifurcate? Is the visible matter in them moving in or out from the center?
Probably because of near or actual collision with other galaxies,
More galaxies are spheriod/elipitical
 
  • #15
Sanborn Chase
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I may have been misunderstood by Mr. Phinds; spiral galaxies when considered over time seem to describe a form similar to an electrical transformer. I don't believe they are electrical transformers, although they may be. I'm trying to understand the reasons for the various forms galaxies take on as they transform one or more things into others. Their forms must follow their purposes.
 
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  • #17
berkeman
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spiral galaxies when considered over time seem to describe a form similar to an electrical transformer.
Say which what?
 
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  • #18
Sanborn Chase
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Have I said something heretical? Is it not proper to assume the stars have arranged themselves so for a reason, and this may be worthy of our scrutiny?
 
  • #19
Have I said something heretical? Is it not proper to assume the stars have arranged themselves so for a reason, and this may be worthy of our scrutiny?
I think we're all confused why a galaxy seems related to an electrical transformer. Perhaps you could explain what you mean?

The motion and arrangement of stars in galaxies is deeply studied. It's really quite interesting!
 
  • #20
phinds
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Is it not proper to assume the stars have arranged themselves so for a reason, and this may be worthy of our scrutiny?
No, the stars do not "arrange themselves". That puts an anthropomorphic spin on inanimate objects and thus is not science. Studying how the stars are arranged is certainly a valid (and interesting) field of study but let's not bring consciousness into it.
 
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  • #21
phinds
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I may have been misunderstood by Mr. Phinds; spiral galaxies when considered over time seem to describe a form similar to an electrical transformer. I don't believe they are electrical transformers, although they may be. I'm trying to understand the reasons for the various forms galaxies take on as they transform one or more things into others. Their forms must follow their purposes.
And you STILL have not explained this apparently nonsensical statement. Please do so.
 
  • #22
Sanborn Chase
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I think it's time to put this transformer thing to rest. First, allow me to extend my thanks to all who have addressed my observation.
In the course of creating a visualization of the of the theoretical sphere of dark matter surrounding galaxies, particularly spiral galaxies, I created an animation very similar to the one posted on this thread. When I then animated these motions through time, I was immediately struck by the similarity of form it described with an old time electrical transformer with primary and secondary coils, etc. I was curious if anyone had a similar experience. This prompted the post. Evidently, no one has; so be it.
Mr. Phinds: please change "arrange themselves" to "are arranged". Incidentally, my wife, who is also a heavenly body, agrees with you wholeheartedly that I'm nonsensical and not very scientific. I've informed her that someone who obviously resides in a very deep pool of knowledge agrees with her.
Merry Christmas to all and goodnight.
 
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  • #23
Excellent end to your post! I love the "heavenly body" comment :)

Many things look like each other and sometimes our minds like to connect them together because of it. A transformer and a galaxy are not related in any significant way but to model a galaxy in your mind as a transformer to recall accurately the structure isn't as bad as not knowing the structure at all!

Have a merry Christmas yourself.
 
  • #24
phinds
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Mr. Phinds: please change "arrange themselves" to "are arranged".
Ah, where's the fun in that. It leaves me nothing to nitpick about.

Incidentally, my wife, who is also a heavenly body, agrees with you wholeheartedly that I'm nonsensical and not very scientific. I've informed her that someone who obviously resides in a very deep pool of knowledge agrees with her.
Well, some of us here are just wading.
 
  • #25
Chronos
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I hope I have expanded your horizons without being offensive. There are many more questions than answers and, hopefully, that will remain true for the foreseeable future. Keep exploring!
 
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