Milky bar

Hum,
Ok.
So we see that our galaxy has two (some would say three) spiral arms just now.
That is related to the angular momentum of the whole galaxy, the density waves move in the same way as traffic jams move backwards or forwards along a motorway.

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In this simple model we see the positions of the traffic jams.

Now if we include satellite galaxies we introduce extra density waves so that a galaxy would have more than two.

 

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So what brought about your change of heart ?

 

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@Anomalous

I assume you are not proficient in English, or have misunderstood what I have been saying.
The arms result from the combination of density waves and shock waves from supernovas (this is just my current opinion of course).

If I was not clear with my previous replies, then I apologise.

You will learn more if you do not resort to (what seemed to me) personal attacks based on what you disagree or misunderstood with what I said.

A simple query will suffice.

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Anyone know where I can get that picture without the arrow and sun in it...

 

Ask and ye shall receive

http://antwrp.gsfc.nasa.gov/apod/ap050825.html