I also guess that it is spiraling inward, contracting into the speculated black-hole center. But what if our galaxy itself is also spiraling and finally contracting into the speculated black hole center of another galaxy (the Andromeda galaxy for example)?
I didn’t think Andromeda was that large. To cause such a spiraling effect, an extremely, extremely large galaxy would have to be involved along with the Milky Way. You are actually talking about a spiraling nebula. Andromeda isn’t big enough to be the center of that large a nebula.
Yes, a spiraling nebula, because Andromeda is not big enough to be the center of that large a nebula. Maybe the whole Local Group (thus: including Milky Way and Andromeda) is contracting into (the speculated black hole center of) the Virgo Supercluster.
Is that supercluster supposed to be spinning??
The speeds of these things is beginning to become a curious issue.
And I don’t take their word for these things too terribly seriously. They seem to speculate a lot.
Practical physics has no astronomy department.
I thought this was a good picture:
… and all made of the exact same affectance stuff.
I guess that the Virgo Supercluster is supposed to be spinning. The Virgo Cluster is supposed to be the central cluster of the Virgo Supercluster, and according to that the black hole as the center of the Virgo Cluster would be the center of the Virgo Supercluster too. Nevertheless, there is a lot of speculation about it.
I can’t really argue with that. Free mass bodies in space are going to be orbiting something that is orbiting something or at very least curving due to something. And as they orbit, they have to be either spiraling inward or outward.
What else is there.
More pointless speculation is a definite possibility. 
In my animations the bodies are also curving (circling) due to a center, but - geometrically said - curving (circling) is merely two-dimensional, whereas spiraling is curving (circling) three-dimensionally.
At the same time when our Earth orbits our Sun, our Sun orbits the center of our galaxy. According to this facts the movement of the Earth can only be three-dimensional, thus spiral.
One can nevertheless call it “circling in a three-dimensional way”, because it means “spiraling”.
I am talking about a geometrical difference - not about spiraling inward or outward (that would be another issue).
The helical model (part 1):
The helical model (part 2):
In the video is said that our solar system would be a vortex. I do not think so. But: The most basic notion that the planets trace helical paths through space is perfectly correct. If you were not aware that the Sun orbits the center of the galaxy — which, since the planets orbit it, necessitates that they trace out helical paths — then the education system has seriously failed.
Emmm…
He seems to be presuming some things. He speaks of an “interstellar wind” presumably due to the Solar System traveling. And although it is impossible to have absolutely zero wind, what makes it reasonable to think that the ambient space (“wind”) isn’t moving along with the Solar System?
As I said: I do not agree with everything he is saying. My intention was to show the spiral/helical model, because I think that he did a good job with his video/animation. But his text is not always agreeable.
I agree that he did a great job with the video. And it points out an often overlooked necessary fact - the helical motion of the planets as the Sun travels.
He also assumes a helical travel pattern for the Sun, which I see no reason to buy into. Why would the Sun be orbiting anything other than the galactic center?
The Sun is only orbiting the galactic center. Did he say something different?
He shows the Sun traveling in a spiraling helix. A helix travel requires a center line/curve to be traveling around. The Sun is shown orbiting that center line (in the same way as the planets are orbiting the Sun) as it travels around the galactic center. What is causing the Sun to orbit like that while also orbiting the galactic center?
Only the galactic center is causing the orbit of the Sun. The spiraling helix he shows is the orbit of the Earth. The Sun is causing the Earth to orbit the Sun, while the galactic center is causing the Sun (and thus also the Earth) to orbit the galactic center. What he shows is that the Earth (but not the Sun) has two orbits: (1) an orbit caused by the Sun, (2) an orbit caused by the galactic center. The spiraling helix he shows is the visual (optical) result of that two orbits of the Earth (and not of the Sun). He does not show another orbit of the Sun.
Watch the path of the Sun in this one:
[youtube]http://www.youtube.com/watch?v=C4V-ooITrws[/youtube]
What do you think is causing the Sun to spiral and bob up and down while making its way around the galaxy center?
Ah, now I know what you mean. I think that he made a mistake there. And by the way: That second animation is not as good as the first one.
I could imagine that he tried to show how the Sun spirals beacuse of the fact that the galactic center also moves, but then he made a mistake by showing odd movements. And it is also not clear why he mentioned the stellar wind in that animation (compare: 1:54-1:58).