Starship Asterisk*

http://apod.nasa.gov/apod/ap091026.html

Nice galaxy cluster, but I was wondering what kind of forces are at work here that got all those galaxies to line up in such nice rows and columns? Is it some kind of electric plasma grid of some sort? Especially the lower right where those galaxies surrounded by the blue halo appear to spell out Galaxy Zoo.

bystander wrote:Nice galaxy cluster, but I was wondering what kind of forces are at work here that got all those galaxies to line up in such nice rows and columns? Is it some kind of electric plasma grid of some sort? Especially the lower right where those galaxies surrounded by the blue halo appear to spell out Galaxy Zoo.

Well, it's a zoo isn't it? A rather old fashioned one, I'd say, with the cages all lined up in rows. No doubt the bars are made of dark matter, held in place by dark energy.

APOD wrote:... the universe has been discovered to create no preferred spin direction ...

Well, duh! Flip'em over and they all spin the other way. It's just chance from which side we see them.

bystander wrote:

APOD wrote:... the universe has been discovered to create no preferred spin direction ...

Well, duh! Flip'em over and they all spin the other way. It's just chance from which side we see them. :oops: :roll:

It's not obvious it should be that way. There's a good chance when you stir something up in the lab that you'll introduce a systematic bias of some sort, and if you look closely enough you'll see that there is some sort of spin bias- even if the mix looks superficially random. So this is a useful observation that (limited by the statistics of the population size) no spin bias is seen in galaxies.

It's chance that we see one side or the other, but that doesn't mean that we would have to see a 50/50 split of spin direction.

Chris Peterson wrote:It's not obvious it should be that way. There's a good chance when you stir something up in the lab that you'll introduce a systematic bias of some sort, and if you look closely enough you'll see that there is some sort of spin bias- even if the mix looks superficially random. So this is a useful observation that (limited by the statistics of the population size) no spin bias is seen in galaxies.

It's chance that we see one side or the other, but that doesn't mean that we would have to see a 50/50 split of spin direction.

OK, so, if there was a bias and we looked one way, the majority of galaxies we see would spin in one direction, but if we looked the opposite direction, the majority would have the opposite spin?

Ha Ha. Spinny minds at APOD. Ha Ha Ha. Such a sense of humours.

bystander wrote:OK, so, if there was a bias and we looked one way, the majority of galaxies we see would spin in one direction, but if we looked the opposite direction, the majority would have the opposite spin?

Right. And in addition to a bias in spin, there could be a bias in orientation, so sorting out the whole jumble to determine if these biases are present is actually not so simple.

Chris Peterson wrote:Right. And in addition to a bias in spin, there could be a bias in orientation, so sorting out the whole jumble to determine if these biases are present is actually not so simple.

In order to determine if it is spin or orientation, wouldn't you need to determine (for lack of a better term) local north for each galaxy? So that you could determine if the left-hand or right-hand rule applies. It seems to me that it would be impossible to determine spin or orientation without knowing which way is up, north, whatever. What is considered local north? How is up in the Milky Way determined?

bystander wrote:In order to determine if it is spin or orientation, wouldn't you need to determine (for lack of a better term) local north for each galaxy? So that you could determine if the left-hand or right-hand rule applies. It seems to me that it would be impossible to determine spin or orientation without knowing which way is up, north, whatever. What is considered local north? How is up in the Milky Way determined?

"North" isn't observed, it is defined. You simply apply the right-hand rule, and you've got north. So now, for every galaxy, you have a fundamental spin axis defined (as a physicist, I'd treat it as the angular momentum vector). You can compare all these axes, and look for an asymmetry in their distribution. That would imply either an actual asymmetry in the orientation of galaxies, an asymmetry in the initial spin directions of galaxies (with respect to some real or arbitrary frame), or a combination of the two. Offhand, I can't think of any way to disentangle those possibilities.

Hello,

the Galaxy Zoo project reminds me of the situation in high energy physics in the 60s. At that time the tracks left behind by particles were analyzed by humans as well. Nowadays this is done with computers.

The image brought up through the 'like yourself' link gave me a momentarily fright!

Chris Peterson wrote:"North" isn't observed, it is defined. You simply apply the right-hand rule, and you've got north. So now, for every galaxy, you have a fundamental spin axis defined (as a physicist, I'd treat it as the angular momentum vector). You can compare all these axes, and look for an asymmetry in their distribution. That would imply either an actual asymmetry in the orientation of galaxies, an asymmetry in the initial spin directions of galaxies (with respect to some real or arbitrary frame), or a combination of the two. Offhand, I can't think of any way to disentangle those possibilities.

If, by definition, all galaxies obey the right hand rule, then, by default, they all spin the same way. So any bias would not be a spin bias, but an orientation bias.

bystander wrote:If, by definition, all galaxies obey the right hand rule, then, by default, they all spin the same way. So any bias would not be a spin bias, but an orientation bias.

My point was that you can't separate the two. A spin bias only makes sense if you have some frame of reference for the spin axis. That's why I suggested angular momentum, since that vector defines both the spin direction and the orientation of the spin axis. What you want to look for is a non-random distribution of the angular momentum vector of galaxies. But if you find one, I don't know how you could decide if that was because the spins were non-random or the orientations were non-random.

BTW, just because "north" is defined by the right-hand rule, that doesn't mean that all galaxies spin the same way. It all depends on your choice of reference frames.

bystander wrote:In order to determine if it is spin or orientation, wouldn't you need to determine (for lack of a better term) local north for each galaxy?

I think that this over-complicates the matter. All that the study has determined is that looking at a fairly large selection of galaxies as they are presented to us in our line of sight, there does not appear to be any clockwise or anticlockwise bias in their directions of rotation. The directions tended to be similar in clusters but were otherwise randomly distributed throughout the sky.

The rotation of the earth or the solar system does not matter. At these scales, we are observing from the the solar system as a point source and the faces these galaxies present to us according to their locations in a map of the sky as seen from earth present no bias in spin direction.

canuck100 wrote:The rotation of the earth or the solar system does not matter. At these scales, we are observing from the the solar system as a point source and the faces these galaxies present to us according to their locations in a map of the sky as seen from earth present no bias in spin direction.

Who said anything about the earth or the solar system. How do you know which way the observed galaxy is spinning if you don't have a reference for direction of that galaxies angular momentum vector (Chris's term). If you assume that the right had rule applies to all galaxies, then all galaxies spin counter-clockwise. Those that appear to spin clockwise are just being viewed from the wrong side.

You have a good point, Bystander, and to your point, I looked up the actual paper and they actually DID take the position in the sky into consideration in the statistical analysis which amounts to what you are suggesting.

http://arxiv.org/PS_cache/arxiv/pdf/080 ... 3247v4.pdf

we herein refer to a clockwise and anti-clockwise classification as Z and S-wise respectively

We wish to establish the large scale statistical properties of the galaxy spins. Although there is some level of uncertainty in the overall (S, Z)-wise number counts, it is still possible to look for a dipole, for example, in the spin distributions.

Rather than using an averaged map, such as that in Figure 3 we fit a probability model to all of the galaxies. The null hypothesis that we wish to test against is that we are equally likely to observe an Z or S-wise galaxies wherever you look on the sky - i.e. statistical isotropy. However, we wish to constrain alternative models in which the probability of observing a Z or S-wise galaxy varies with position on the sky ( the sum of these probabilities must always equal one).

This is not assigning a specific value of angular momentum to each galaxy but it the statistical equivalent of doing so in this situation.

Their bias and how they tested for it is also rather interesting.

They actually found a bias in favour of S spin

In this paper we are interested in the projected spin classifications of the spiral galaxies; the galaxies classified asclass=2 or class=3. We find (17,100, 18,471) of the spiralgalaxies are cleanly classified (i.e. over 80% weights) with(Z, S)-wise winding sense respectively, with equivalent (Z,S)-wise number counts of (6,106 , 7,034) for the supercleansample.
For a null hypothesis of statistical isotropy we would expect (Z, S)-wise handedness to be equally likely across the sky, however we observe a significant excess of S-wise galaxies in both our samples, at more than 7 significance2.

The original study had been of 291,626 galaxies. So they created mirror images of 93,000 galaxies from their original data and had them separately categorized by the same users. The ended up with the same S bias, and to the same degree from which they concluded that the bias was likely neurologically inherent.

We find that the average (Z, S)-wise weights are (5.5%, 6.0%) for the monochrome images. . . . The fact that the weights stay the same within statistical accuracy indicates that we have a significant level of bias in our results, and no true S-wise excess.

By the way, the original data set from which the spiral galaxies were drawn was 893,212 galaxies from 85,276 users. If I recall correctly, I read elsewhere that the Galaxy Zoo likes to have about 50 responses for each galaxy in order to eliminate errors and use results that have a high level of confidence.

Machine intelligence? Definitions of intelligence include 'understanding'. According to definitions 'understanding' involves knowing the truth. A machine can only be programmed to sort information, it can never 'know the truth' .. as that concept seems to be beyond most human minds.

mishkin wrote:Machine intelligence? Definitions of intelligence include 'understanding'. According to definitions 'understanding' involves knowing the truth. A machine can only be programmed to sort information, it can never 'know the truth' .. as that concept seems to be beyond most human minds.

This from a man who doesn't know what the Turing test is.