200,000 Elliptical Galaxies Point the Same Way

KentuckyFC sends us to arXiv, as is his wont, for a paper (abstract; PDF preprint) making the claim that 200,000 elliptical galaxies are aligned in the same direction; the signal for this alignment stands out at 13 standard deviations. This axis is the same as the controversial alignment found in the cosmic microwave background by the WMAP spacecraft.

Comments

Why?

[bcmm]

Do they give any reason that this might be so? Are the galaxies in the same area? Did they all form from some insanely massive rotating structure or something?

Re:Why?

[iluvcapra]

It might mean that the angular momentum of the universe is nonzero, if a majority of them are turning the same direction. Or, even if they all cancel out, that momentum in the early universe tended to be oriented in a plane. (IANAP, just a guess but seems logical)

I'm curious if the Milky Way is a part of the alignment.

Re:Why?

[fygment]

The author states that the reasons for the orientation are beyond the scope of the paper. But the implication of the orientations is that the universe is not spherical. I have had only one course in cosmogeny (origins of the universe) and all the models lead to symmetry. So any indication of a lack of symmetry implies that we are missing some big piece of the puzzle. Combine this with the tenousness of many of the theories of cosmology (eg. Big Bang ... far from perfect and getting further ) and the picture emerges that there is not a lot that is actually known about the structure of the universe. Despite all the bravado and pat statements in the media, all we have are half-baked guesses. Mind you, does it really matter? Given our very short lives in the grand scheme of things, the lack of knowledge probably isn't hurting us.

Re:Why?

[ATMD]

OK, I may be making a fool of myself here, but how can the entire Universe's angular momentum be non-zero? Surely momentum can only ever be relative to your frame of reference - and by definition, any frame of reference you can think of will be within the system you're trying to measure.

Although... thinking as I type here... say you were sitting on a massive spinning top, and all you could see was the spinning top. You'd still feel centrifugal force, as a result of its spinning. Could be an interesting explanation for dark energy?

(and yes, now I remember that important word "inertial" from A-level Physics lessons. Meh...)

Re:Why?

[Maury Markowitz]

> Brans-Dicke theory and it shows nothing about angular momentum

You're right. That sucks.

Basically the idea behind BD, and the other ST and STV theories, is that there is an additional field, not just the tensor field of GR. One of the side-effects of the field in the BD theory is that angular momentum "falls out" of the universe. This is actually kinda important.

In traditional models, the conservation laws you know don't really _have_ to exist. For instance, if the universe was shaped like an egg, billiard balls would always roll into one corner of the table because there's more mass on that side of the universe. The fact that it is conserved says a lot about the universe, specifically that is symmetric around any point in 3-space. Conservation of angular momentum is similar; it says the universe is symmetric around other axis as well -- linear momentum would still be conserved in a universe shaped like a cigar, along any axis the gravity is still even, but in this case a spinning object would speed up and slow down. Conservation of energy is due to the fact that the universe is symmetrical in time, physics in the past is the same as it is today.

Ok, but like I said, those laws don't _have_ to be true, and this bugged the hell out of a lot of people over the years. I forget which one of them, I think Brans, was thinking about what would happen if you spun a dish full of water in an empty universe... would the water rise up the sides? And if it doesn't, why not? Isn't either answer a little weird?

The extra field in DB theory answers the question -- the answer is "yes", the water will rise up on the sides. It wasn't designed to do that, at least I don't think so, but it ends up popping out of the math.

So basically if you end up with odd angular momentum terms in the universe, it MAY suggest that some other model of gravity might be more correct. Right now everything we've ever measured can't tell between the various models, but this might.

Maury

Assumption busting...

[massivefoot]

Huh. I don't really have a great deal of specialist knowledge on cosmology, but this seems to put a lower bound on the distance over which we can assume the universe is isotropic (i.e. the same in all directions). The abstracts puts an upper bound on the redshift of the galaxies involved in the survey, which is presumably roughly equivalent to limiting the distance they are from us, but surely the fact that this net angular momentum axis is closely aligned with an axis identified in WMAP data indicates that this is a far larger scale phenomenon?

Re:Assumption busting...

[pla]

this seems to put a lower bound on the distance over which we can assume the universe is isotropic

I have to wonder - Could this particular anisotropy account for the Voyager paradox? That would set a much lower bound...

Even if not, though, I really find this sort of anomaly fascinating. Almost everything cosmology has found since the dawn of modern science has pointed to a bleak, cold, basically empty univers that goes on identically forever in every direction. Even learning that the universe has some underlying structure would somehow seem a lot more comforting.

A grain of salt

[Stranger4U]

I read the article, and there seem to be a few problems he doesn't really address. First, he assumes that all elliptical galaxies have a point-of-view from which they appear circular. I don't think anyone has determined this to be the case, and he doesn't really have a way to get this from his data. Secondly, he doesn't give much real discussion to the error in the measurements, which is significant. No preffered axis of alignment would fall well within his measurement uncertainties. Finally, the 13-standard deviations is not from any real sort of error propagation, but from some random computer generated results. Could be interesting, but to be taken with a grain of salt.

Why Not?

[NReitzel]

Einstein did not say that there cannot be a center of the universe.

What he did say is that for the purposes of measurement, there exists no privleged metric. All this says (All?!) is that there is no overall coordinate system that will be superior to all other coordinate systems.

If things started out as a big bang, on some scale, we will find a "center" of the universe. Is this an astronomy-shaking discovery? No. Maybe a tremor or two, for diehard relativeists. We already know that for specific purposes, there is often a preferred metric for computational or navigational purposes. Remember back in the Apollo program when the physics guys tried to explain that at a specific point, the coordinate system for the spacecraft shifted over from Terra-centric to Luna-centric, and the reporters looked at the "jog" in the plot and asked if the spacecraft would feel a "lurch" as it passed this point?

It's not nearly as big a deal as, say, whether Pluto is a "planet" or not. Pick a label, pin the sticker on the rock, except in this case, the rocks are superclusters of galaxies.

Re:Translation?

[Vellmont]

can someone give me the 'play by play' brief on the significance of the orientation of the galaxies and why the chance is so slim that they align as they do?


I'm not a Cosmologist, but one would expect galaxy orientation to be pretty much random. As an example, think about if you threw a bunch of nails in the air. At any given time you'd expect the nails orientation to be pretty random (ignoring air effects, and any bias given by your throw). If they all aligned in a certain way though, you'd be surprised and start looking for a cause. (In this case say a strong magnetic field in the room).

If this is true, there must be something orienting the alignment of galaxies. That could be either some bias in the big-bang, some outside force we don't understand, or something else.

Little discussion of instrumental systematics

[JohnnyDanger]

This paper has no discussion of the ellipticities caused by imperfections in the telescope optics. This is a well known problem for weak gravitational lensing and cosmic shear measurements, which also use measured ellipticities. This problem can be corrected by using the stars (which should be round at the telescope resolution) to figure out and fix the distortions in the image.

I have little direct experience with this, but I suspect that optical distortions could be the cause of the effect he is seeing. The universe may very well have some weird features, but this paper is not a careful analysis.

Re:Centre of the universe

[FuzzyDaddy]

"Fingers of God" is unrelated to the current paper. Fingers of God is an apparent anisotropy, while this paper describes an actual anisotropy.

The fingers of god effect is simple - the doppler shift of a galaxy is proportional to the distance, according to Hubble's observations. If you do a plot of galactic positions, using the observed position in the sky and the red shift as the third dimension, you see what appear to be long, skinny clusters, all pointed directly at you. This happens because in tight clusters, galaxies are attracted to each other gravitational and have a range of velocities which is relatively large. So there's an added velocity on top of that caused by the expansion of the universe, which changes the distance you'd compute by Hubble's law.