B Spiral galaxies: Multiple axies of rotation?

[Buckethead]

Spiral galaxies of course rotate around one axis perpendicular to the plane, but has anyone measured if any spiral galaxies are also rotating about an axis through the plane or about any other axis?

 

[Vanadium 50]

An object can only rotate about one axis. Angular momentum is a vector and has a unique direction.

 

[Buckethead]

a gyroscope spinning on a pedestal has two axes of rotation.

 

[FactChecker]

a gyroscope spinning on a pedestal has two axes of rotation.

Not when looked at correctly. There is one axis of rotation and that is the most concise way to look at it. It can be decomposed into two components. Our brain likes to conceptually decompose the rotation into rotations around two axis because of the symmetry of the gyroscope, the great dominance of the rotation around the mechanical axis of the gyro, and the obvious motion of that mechanical axis.

 

[Buckethead]

If I spin a sheet on paper on a desk while simultaneously rotating it around an axis that is parallel to and intersects the desk, that this is only spinning on one axis?

 

[FactChecker]

If I spin a sheet on paper on a desk while simultaneously rotating it around an axis that is parallel to and intersects the desk, that this is only spinning on one axis?

This got me thinking about a different problem where the gyro is spinning and also rotating around another axis parallel to the gyro axis, but offset. I don't think that I can say that the motion can be represented by a rotation around a single axis. The axis are parallel, so a single axis creating that motion would also have to be parallel, just offset. But I don't think that a single axis could create that motion. I may have been confusing the angular momentum with the actual physical motion.

 

[Chronos]

A galaxy is not a rigid body and N body systems, like a galaxy, have very complex interactions rendering all individual orbits unique. The orbital axes and inclination of any gravitationally bound system can therefor only be generalized. Don't forget orbits are necessarily elliptical and everything tugs on everything else,.

 

[Buckethead]

A galaxy is not a rigid body and N body systems, like a galaxy, have very complex interactions rendering all individual orbits unique. The orbital axes and inclination of any gravitationally bound system can therefor only be generalized. Don't forget orbits are necessarily elliptical and everything tugs on everything else,.

OK, but still, the rotational curve of a spiral galaxy is observable when the stars and gas are taken as a group. My question relates to imagining a pencil poked through a sheet of paper so the pencil is perpendicular to the plane of the paper, then spin in around the axis parallel to the length of the pencil, typical spiral galaxy. But what if the pencil were not quite perpendicular, then the galaxy could still spin but would "wobble" and the edges of a galaxy face on would appear to be oscillating toward and away from the observer. So I was wondering if anyone has attempted to measure this. If it turned out to show an oscillation, this would have to indicate (I think) that the dark matter surrounding the galaxy would be more cylindrical in shape since this wobble would indicate that any given star was not orbiting the center of the galaxy but instead would be orbiting a gravitational area above or below the galaxy plane. Just thought it might be an interesting way to further characterize a dark matter shape.

 

[Vanadium 50]

Why do you think taking a galaxy with cylindrical symmetry and adding a cylinderically symmetric distribution of dark matter will yield a cyllinderically asymmetric angular moment?

 

[Buckethead]

Why do you think taking a galaxy with cylindrical symmetry and adding a cylinderically symmetric distribution of dark matter will yield a cyllinderically asymmetric angular moment?

My initial though was if you take my crooked pencil example and paint a dot somewhere near the edge of the paper, Most single dots will always orbit the pencil at one point a fixed distance above or below the intersection of the pencil and paper. A star would not be able to do this if the center of mass was a point at the center of the galaxy as it would eventually be sucked down toward the center. It could only do this if the gravitational field were cyllindrical in shape. Such a galaxy would appear to have edges that have an oscillation in their distance from us for galaxies face on.

Although after thinking about this a bit more I can see this would be statistically impossible and more than likely the galaxy would look like a giant cylinder which clearly it is not, so I guess that answers my question. (I think).

OK, so the bottom line is it is simply (almost) impossible for a disk to wobble in this way. But still, has anyone actually measured this parameter (wobble oscillation)? In this universe where almost anything can happen, it seems like an interesting experiment.

 

[CygnusX-1]

Spiral galaxies of course rotate around one axis perpendicular to the plane, but has anyone measured if any spiral galaxies are also rotating about an axis through the plane or about any other axis?

Go to StartPage and do a search on "polar ring galaxy."

 

[Buckethead]

Go to StartPage and do a search on "polar ring galaxy."

Wow, that's great! Thanks for turning me on to that. This doesn't directly address my question, but I'm glad I just learned something new!

 

[russ_watters]

The axis of revolution of the stars has to be perpendicular to the galactic plane, otherwise the stars wouldn't be orbiting the center of mass. They'd either fall out of orbit or be pulled into the plane. It's the same reason our solar system is planar.

 

[Chronos]

The orbital plane of the solar system, aka the ecliptic, is only approxmately flat , The orbital inclination and even center of mass between each planet and the sun is unique and dynamic, not fixed.

 

[russ_watters]

The orbital plane of the solar system, aka the ecliptic, is only approxmately flat , The orbital inclination and even center of mass between each planet and the sun is unique and dynamic, not fixed.

In real life there is never such a thing as perfection, so I don't see a point to this objection. The variation in the inclinations is only +-3.5 degrees. It would be very difficult for there to be one with a 30 degree inclination, for example.

Note, this also isn't very well related to the OP's question, which stipulates to the planar shape.

 

[stefan r]

Spiral galaxies of course rotate around one axis perpendicular to the plane, but has anyone measured if any spiral galaxies are also rotating about an axis through the plane or about any other axis?

Spiral galaxies rotate around their galaxy clusters. The cluster's axis of rotation is mostly independent of the galaxy's axis of rotation.

 

[russ_watters]

Spiral galaxies rotate around their galaxy clusters. The cluster's axis of rotation is mostly independent of the galaxy's axis of rotation.

I can't parse this. Did you mean to say "revolve" anywhere?

 

[stefan r]

I can't parse this. Did you mean to say "revolve" anywhere?

I meant the cluster rotates and is made up of galaxies (plus some other stuff). An individual galaxy is revolving around the cluster. Would it help to write "galaxys' axes of rotation are independent of each other and the cluster"?