M81, galaxy spin direction? (APOD 27 April 2007)

brbear1 · Post by **brbear1** » Fri Apr 27, 2007 4:18 pm

As I study the image of M81 used as the APOD on April 27th, it appears different from the way I had always imagined spiral galaxies to be. I have always thought of them as a disc existing in a particular galactic plane. This picture (due to its depth?) has the appearance of a funnel where if you could start a ball rolling at the end of one of its spiral arms it would spiral down to the the bottom ending at the galactic center (or its supermassive black hole, where, of course, there is no bottom.)

BMAONE23 · Post by **BMAONE23** » Fri Apr 27, 2007 4:52 pm

I see what you mean. The creamy caramel center does appear to sit farther down than the icy rock candy exterior http://antwrp.gsfc.nasa.gov/apod/ap070427.html

NoelC · Post by **NoelC** » Fri Apr 27, 2007 6:23 pm

Well, there are the gravitational influences of Holmberg IX and a bit more distantly (and out of the APOD frame) M82 to consider...

From what I've read, the influence of the other galaxies may help explain why there are many young blue stars in M81's arms, and even why the spiral arms are as prominent as they are.

-Noel

brbear1 · Post by **brbear1** » Fri Apr 27, 2007 8:38 pm

What really gave me the impression that M81 is shaped like a funnel or a saucer is the great photo I found when I clicked on the words in the caption "this remarkably deep image" and went to the Gallery of Astro Photography. The purplish dust lanes between nine o'clock and twelve o'clock from the galactic center give the picture/galaxy a three-dimensional quality. It is photos like this that cause me to check on the latest from APOD each day.
[/u]

Keith · Post by **Keith** » Wed May 02, 2007 10:59 am

Looking at the recent APOD image of M81 it appears to be spinning anti clockwise from our standpoint. Do all galaxies have a uniform spin direction or is there a majority direction, or are they all totally independant?

Andy Wade · Post by **Andy Wade** » Wed May 02, 2007 4:43 pm

Keith wrote:Looking at the recent APOD image of M81 it appears to be spinning anti clockwise from our standpoint. Do all galaxies have a uniform spin direction or is there a majority direction, or are they all totally independant?

Doesn't it depend on your viewing position?
If I was at the other side of M81 it would appear to be spinning clockwise.
Or were you just referring to whether they are all spinning in a similar direction from our viewing position?

BMAONE23 · Post by **BMAONE23** » Wed May 02, 2007 5:15 pm

Perhaps what is needed is a way to determine if these larger scale structures (galaxies) develop larger scale polar magnetic fields and then determine the direction of rotation relative to these large scale magnetic fields. (Maybe EU theory could take a step foreward (or backward) if these fields could be proven to exist and could be quantatively measured.)

kovil · Post by **kovil** » Wed May 02, 2007 5:50 pm

Article titles aside; they present some interesting ideas, tho they do not prove their premise, they are worth considering and pursuing for more data.

Correlating anomalies of the microwave sky:
The Good, the Evil and the Axis
Authors: Aleksandar Rakic, Dominik J. Schwarz
http://arxiv.org/abs/astro-ph/0703266v2

Is the Cosmic "Axis of Evil" due to a Large-Scale Magnetic Field?
Authors: Michael J. Longo
http://arxiv.org/abs/astro-ph/0703694v2

Does the Universe Have a Handedness?
Authors: Michael J. Longo
http://arxiv.org/abs/astro-ph/0703325v2

Extragalactic Radio Sources and the WMAP Cold Spot
Authors: Lawrence Rudnick, Shea Brown, Liliya R. Williams
http://arxiv.org/abs/0704.0908v1

High Galactic latitude interstellar neutral hydrogen (HI) structure and associated acoustic-scale WMAP hot spots
Authors: Gerrit L. Verschuur
http://arxiv.org/abs/0704.1125v1

Keith · Post by **Keith** » Wed May 02, 2007 5:58 pm

Andy Wade wrote:
Keith wrote:Looking at the recent APOD image of M81 it appears to be spinning anti clockwise from our standpoint. Do all galaxies have a uniform spin direction or is there a majority direction, or are they all totally independant?
Doesn't it depend on your viewing position?
If I was at the other side of M81 it would appear to be spinning clockwise.
Or were you just referring to whether they are all spinning in a similar direction from our viewing position?

Well I think that, irrespective of our viewing position, their spin has an absolute vector. Two observers on either side of the same galaxy would see different spin directions, but the galaxy spins only one direction. So viewing position aside, do they all spin in the same direction? Do astronomers catalogue (even perceived) spin direction?

AZJames · Post by **AZJames** » Mon May 21, 2007 2:55 am

From our perspective, I would agree that M81 appears to be spinning in a counter-clockwise direction. I use as my model the appearance of water spinning as it goes down a drain. Thus the shape of the spiral arms appears to conform to my model of a counter-clockwise spin.

Of course, viewed from the opposite side of M81, the spin is clockwise. I infer from this that to any observer in the universe, the spin direction of spiral galaxys has an equal probability of being either clockwise or counter-clockwise.

But I have a problem. If all galaxys are embedded in vast clouds of Dark Matter, why should the spiral arms be 'spiral' shaped - why shouldn't they be in concentric circles or concentric arcs? In other words, why shouldn't they resemble the rings of Saturn? Or, for that matter, the structure of the Solar System?

To my mind, the only reason why spiral arms are 'spiral' shaped is because there is an inward moment to their motion - especially for those portions of a given arm which is closer to the central mass of the galaxy. This implys a very significant radial gravitational gradient. But the presence of the Dark Matter should result in an extremely weak gradient, outside of the 'bulge' area.

So, why are spiral arms 'spiral' shaped?

Keith · Post by **Keith** » Mon May 21, 2007 8:01 am

I agree that the position of the observer has perceived relevance, but there should still be an absolute answer to the question. Possibly, the question is almost meaningless because galaxies can be oriented in any plane. But viewed from an absolute standpoint,there may be an absolute answer to the question, even if it is no.
So viewing position aside, has anyone out there done enough observation to say - you know what? They're all anti clockwise
All neutrinos have left handed (or anti clockwise) spin.
Although as far as spiral arms were concerned, I thought the idea was that was an outward component caused by their spin, against inertia and gravity, but I'm not a real astronomer so I haven't done the math. It's pretty well understood though.
I'm leaning towards the answer ebing random, but if anyone out there has done a lot of observation (which I haven't) - do they have a view?

Pete · Post by **Pete** » Mon May 21, 2007 9:23 pm

If the sum of the angular momentum vectors of all observable spiral galaxies are not (close to) zero, then the Universe has a net rotation, which should be observable in the cosmic microwave background, but no such anisotropy has been found...

Isn't it impossible to be able to define an 'absolute' direction in this universe?

As for galactic spiral arms, differential rotation rules out the possibility that the spiral arms are permanent arrangements of stars; spiral arms are not collections of stars moving as one group in their galaxies. Rather, they're density waves propagating through the spiral galaxy's disk. The spiral pattern rotates slower than the stars in the disk, which themselves move on essentially circular orbits.

So why are they shaped like spirals? According to spiral density wave theory (as documented on Wikipedia), that's the shape that naturally arises from the alignment of stellar elliptical orbits. (check out the diagram on the wiki page)

Some spiral galaxies have circular rings around their bulges, like the galaxy NGC 6028, also called Hoag's Object: http://apod.nasa.gov/apod/ap020909.html

rigelan · Post by **rigelan** » Mon May 21, 2007 11:38 pm

If neutrinos have a spin, that spin has a vector which is compared to the velocity vector of the neutrino. But if you don't define the spin with regard to an observer or with regard to a single direction, you cannot get any real numerical data out of it.

Of course, defining the direction is child's play. Anybody want to set the north star as direction 0,0,0 ?

AZJames · Post by **AZJames** » Tue May 22, 2007 5:32 am

Thanks Pete.

I feel a little foolish I didn't check the Wiki article first.

I spent a little time with a CAD drawing program to explore variations on the drawing in the Wiki article to satisfy my curiosity. It turns out that an ordered rotation of the elliptical orbits of gas, dust and stars will always result in just two spiral arms - they just get wider the more you rotate the orbital paths.

So it would seem that there is an element of chaos in the order (

), to account for multiple spiral arms.

I shall have to do some more reading on the subject.

brbear1 · Post by **brbear1** » Tue May 22, 2007 1:29 pm

What is the possibility that the universe itself is arranged like a spiral galaxy?

Starship Asterisk*

M81, galaxy spin direction? (APOD 27 April 2007)

M81, galaxy spin direction? (APOD 27 April 2007)

Galactic spin direction? (APOD 27 Apr 2007)

Re: Galactic spin direction? (APOD 27 Apr 2007)

Re: Galactic spin direction? (APOD 27 Apr 2007)

a spiral galaxy universe