Clockwise vs Anticlockwise?

[erick]

Looking at today's APOD

http://antwrp.gsfc.nasa.gov/apod/ap080614.html

I found myself wondering on the relative proportions of clockwise and anticlockwise spiral galaxies that we observe from our vantage point on earth. Logically I would expect equal numbers? A bit of internet searching turned up:-

Referring to the GalaxyZoo project, a poster said:- "A recent and ongoing study (http://www.galaxyzoo.org/) shows that the direction of the arms in spiral galaxies is uniformly distributed in 'all' directions. That is, no regions have been found with concentrations of clockwise or anti-clockwise rotating galaxies. A previous smaller study seemed to indicate that there was such a 'preference'. The larger study seemed to confirm that at first, but when presented with mirrored images, the 'preference' stayed the same. So it seems it was human error: a human viewer would have a preference in seeing a certain rotation when the image wasn't very clear. Careful analysis of the classification of regular and mirrored images shows no preference in either rotation."

So 50:50. Is that what you understand it to be?

[xelasnave]

May I ask if anyone knows this...
Are galaxies "unwinding" or "winding up"...or are the out lying stars of a galaxy moving in to the center or out to interstellar space???
alex:):):)

[stephend]

They're just going around; not in and not out.

Why do they have arms? Well, why do you have arms?

[Dog Star]

My humble understanding of the matter was that they were in fact unwinding (that's if I understand the situation correctly)
I'm only an arm chair physicist, but given that a black hole allegedly exists at the centre of our galaxy, shouldn't we expect to find the opposite effect?:shrug:

[xelasnave]

I can never see how a black hole can influence the rest of the galaxy..gravity travels at a speed most are happy to agree is that of C..therefore any message of gravity must take this into account..it is also clear that black holes clean out the available material within their gravitational influence..but not further...
Now that if one conceeds to the belief that such theoretical objects such as those envisaged by ??? the guy in the trenches working on the latest formuleas derived by Gr A....and of course I reject the notion hat black holes do exist simply because an extrapolation of the general relativity sums suggest that a point will be reached where matter does the job attributed to a black hole...anyways had to mention that...

The Moon is moving away and so I wondered if other bodies do similar..out lying stars for example..the Moon moves out because of the push of gravity ..the outter stars move faster becasue gravity pushes so on my view of the universe (a push universe that is) one should expect the outlying stars to be moving out not in...

I doubt if galaxies stay the same...matter could be presumed to be "sucked in" or on the other hand "pushed out"

alex

[xelasnave]

I feel it may be an incorrect move to interpret the Universe so as to parallel it to human experience.

Arms is a poor choice of words from our science ..what prompted science to be so casual that it would seize on such an unusable terminolgy to describe what we see.... what we see are galactic pattens and unrelated to human experience and presumable not explainable by calling upon the substitution of human parts for a body bearing no manner of resemblance to a human or any other animal for that matter.

alex:):):)

[Ian Robinson]

Neither , they are in stable orbits about the centres of their galaxies.

As to left or right handedness in spirals in galaxies - the universe doesn't care and the it's a normal distribution.

[Chrissyo]

Yeah, 50:50. As I understand it, if it wasn't a 50:50 ratio, it would appear as though the universe had a preference for one specific direction. However, that contradicts some of the big understandings of cosmology (if I recall correctly, on large scales the universe is supposed to be relatively homogeneous).

Hence, there was some interest in the initial GalaxyZoo study as it appeared to be showing that there was a preference. Big trouble. But upon further thought, it turned out to be merely the way our human brain interprets images of spirals. To test this, they flipped the GalaxyZoo images - if there really was a preference then the other direction would start getting more hits, but if it was just human interpretation then the same results would be gathered. As I understand, the same results were obtained - it was just a human brain thing.

That's my understanding of it all. I may have gotten some details wrong though. Someone with more info will hopefully be along soon.:P

[stephend]

Scientific American has some good info on spiral arms:

http://www.sciam.com/article.cfm?id=what-process-creates-and&page=2

I like the bit where it says computer simulations spontaneously generate spiral arms, too, but no-one can figure out why it happens inside the computer, either.

It appears there is not much difference in star density in the arms and in the spaces between the arms, just enough to be visible.

[erick]

Thanks everyone, this is useful information. :)

[bojan]

This is a very informative article..
The results of the simulation (formation of spiral arms as density waves) clearly show that our basic understanding of gravity force and the mass distribution on the galactic scale is correct and that there are no other "mysterious" forces involved...

[Screwdriverone]

Umm, isnt the rotation of the galaxy in question subject to the viewer's point of view? That is if we see the galaxy supposedly looking like it is an anticlockwise spiral, won't it be a clockwise spiral if viewed from the other side?

I suppose that everything by default must be referenced as seen from Earth, but in this case, what point of reference is valid? The fact that it is related to interpretation and not fixed to a unbiased or central reference point must mean that the statistical data is therefore inconclusive?

I saw that observation in the UK Sky At Night Magazine's article on Galaxy Zoo and thought it was also quite funny as to how most of the errors generated in galaxy selection by the users were created by human laziness in as much as it was easier to select the first entry in the drop down box than actually select the correct selection for the galaxy being observed. All that time and effort potentially undone by the poor slobs who drove it. :lol:

Cheers

Chris

[Chrissyo]

The idea is (again, assuming I understand this correctly) - every point in space is more or less the same as any other point in space. Hence, the distribution from our point of view should be the same as the distribution from any other point of view (within statistical fluctuation, that is).

Also, I'm just trying to picture it in my head - but if there was a definite trend from one point in space, I think we'd be able to see a trend as well. We wouldn't see a random distribution.


That is a shame. Hopefully they have the ability to rate each user based on how 'accurate' their selections are (based on an accurate average for each galaxy perhaps). And I guess it only really effects the spiral rotation selections - even for sloppy work I don't think it would be too easy to mistake a spiral galaxy for an elliptical... though if I remember from my time at GalaxyZoo, some of the 'star' objects can be easy to mistake for dim ellipticals. OK, let's hope they can judge good classifications from bad ones. :lol:

[sjastro]

I suspect the researchers are trying to say is there no preferential direction of rotation for spiral galaxies in which case a point of reference is not necessary.

What is interesting if this principle is applicable to galaxy clusters and groups.

Regards

Steven

[erick]

Yes, as I understand it there is no "up" in space until you define it for yourself in some way - an visual orientation of some object, the perceived direction of the major gravitational force.... (I love the way that poor old Venus has an axis tilt of 177.4 deg!! - by our definition of what constitutes North)

I also understood that lots of work has shown that the universe is homogeneous on the large scale, so I was expecting the answer to be that the distribution is 50:50, from our observing position. And presumably, from any observing position in the Universe.

[mellotron]

The spin is caused by the combined gravitational forces of its of its neighbours during formation, which is effectively random, so you would also expect the distribution of spin directions to also be random.

How do we determine the spin direction of edge-on spiral galaxies? Sounds like it could be arbitrary.

[Suzy_A]

You can define the direction of 'spin' by other properties - usually the galaxy's magnetic poles, so you can define north and south and hence 'up' and 'down' and the 'spin' in relation to those.

Someone mentioned something about that everything in the Universe is 50:50...

Back to Quantum Mechanics and Relativity and cosmology....

One of the consequences of a current interpretation of QM and R is that after the Big Bang in which basically everything was energy and then as the Universe cooled and expanded, particles were formed from the energy. Included in this were electrons-positron pairs, most of which annialated each other to form gamma photons. However there was a slight excess (about 0.0000...001%) of negative electrons and so as a result atoms were able to form from the protons and negative electrons.

In other words, for some reason, the Universe had 'handiness' ie a preference for one way over the other.

Similarly, many molecules have a handiness which prefers their arangement for one isomer over another, and this is the root cause of why many sea shells, vines, or whatever prefer one spiral form over the other. I think from memory... clockwise...? is prefered?

Anyway, the other thing is that there possibly is no actual spiral in galaxies, rather it is an effect of a shockwave that propogates through that causes density variations in interstellar matter. This in turn has two effects - one is it gives the appearance of a spiral, the other is that it actually generates a spiral as the density variation leads to new nebular and star formation as the shockwave moves through space. Rather than the stars moving around in a spiral, the shockwave generates the illusion of a spiral as new stars etc are formed. I suppose an analogy is the formation of a lenticular cloud forming over a hill, although this is the opposite case in which the cloud stays stationary due to a stationary disturbance despite the air moving.