Axis of Evil? Or Axis of Opportunity?
Posted by John Baez
This paper argues that the axes of elliptical galaxies don’t point in random directions. but have a slight tendency to point roughly towards the ‘axis of evil’. The ‘axis of evil’ is a controversial concept in itself: a direction that seems to be picked out by anisotropies in the cosmic microwave background!
Trying to put a more positive spin on the idea, the author calls it the ‘axis of opportunity’:
- Michael J. Longo, The axis of opportunity: the large-scale correlation of elliptical galaxies.
I thank Daniel Rocha for pointing out this paper to me.
Here’s an elliptical galaxy:
It’s called ESO 325-G004, and it’s about the mass of the Milky Way. It’s in the middle of Abell S0740, a cluster over 450 million light-years away in the direction of the constellation Centaurus.
Longo has analyzed a sample of 200,000 of elliptical galaxies with redshifts < from the Sloan Digital Sky Survey. They look round when their spin axes are pointing directly towards us, and like more or less eccentric ellipses otherwise. So, by correlating their observed shapes with their positions in the sky, one can see if their axes tend to point the same way.
The author claims that yes, there’s a statistically significant tendency for them to point towards the direction with right ascension and declination . In fact, he claims the effect is very strong. Interestingly, the quadrupole and octopole moments of the cosmic microwave background radiation (or CMB) seem to pick out roughly similar directions as being important.
Since I’m not an expert on this stuff, I can’t evaluate this paper. So, all I have is a lot of questions.
How convincing is the statistical analysis in this paper? Longo claims a high degree of statistical significance… but what about his method?
(I note that Longo only studies the amount of apparent ellipticity of the galaxies he studies, not the directions these ellipses point. It would be fun to take the directions into account, and see if they confirm his results. But, that’s sort of a separate issue.)
What’s the current conventional wisdom on the ‘axis of evil’? I see only a few papers on it on the arXiv, mainly by a handful of supporters, including Kate Land, Joao Magueio, and the author of this paper, Michael Longo. Magueio has been called the ‘bad boy of cosmology’ for his support of variable speed of light theories, and Longo has proposed an explanation of the axis of evil based on magnetic fields. Neither of these facts inspire confidence in me.
Furthermore, I’ve seen just one paper trying to explain away the axis of evil. Usually when an anomaly is taken seriously, you find more debate in the literature. Maybe I’m not looking in the right places?
On the other hand, even that bastion of reasonableness Sean Carroll has studied cosmological models with a preferred direction — and he doesn’t dismiss the axis of evil off-hand:
The claim that there actually is evidence for a preferred direction in the CMB goes by the clever name of the axis of evil. If one looks closely at the observed anisotropies on the very largest scales, two interesting facts present themselves. First, there is less anisotropy than one would expect, on very large angular scales. Second, and somewhat more controversially, the anisotropy that does exist seems to be oriented along a certain plane in the sky, defining a preferred direction perpendicular to that plane. This preferred direction has been dubbed the “axis of evil”.
Is the axis of evil real? That depends on what one means by “real”. Nobody has a theory that predicts CMB anisotropy directly as a function of position on the sky — rather, theories like inflation probabilistically predict the amplitude of anisotropy on each angular scale.It does seem to be there in the data. On the other hand, maybe it’s just a fluke. But at each scale there are only a fixed number of independent observations one can make, implying an irreducible uncertainty in ones predictions - that was the original definition of cosmic variance, before we re-purposed the phrase. For what it’s worth, the actual plane in the sky defined by the large-scale anisotropy seems to coincide with the ecliptic, the plane in which the various planets orbit the Sun. Many people believe it’s just some local effect, or an artifact of a particular way of reducing data, or just a fluke — to be honest, nobody knows.
So, maybe that’s the conventional wisdom — “nobody knows”.
Re: Axis of Evil? Or Axis of Opportunity?
Interesting. I’ll read that paper, thank you.
Back in my MSc dissertation, I studied the center of the Shapley Concentration, the cluster of galaxies A3558. Then, I noticed something very curious, that I have reported in my paper:
Evidence of Substructure in the Cluster of Galaxies A3558 Dantas et al.; Astrophys.J. 485 (1997) 447.
I copy here the relevant part:
we qualitatively note a preferential alignment at the 45 deg position angle of a diverse set of features in this cluster, ranging from small to large scales. An application of the Lee-statistics (Fitchett 1988) to this cluster also indicates that the 45 degrees direction has a greater probability of bimodality. This alignment coincides with (a) the major axis PA of the dominant galaxy, (b) the major axis PA of the isocontours of the central core (using AK/WT maps as well as a X-ray countour map), (c) a marginal velocity gradient direction across the central bimodal substructures, and (d) the direction of alignment of major subclumps, namely the bimodal core and SC1327-312. This alignment seems to persist even beyond the analysed field. A qualitative inspection of an isopleth map of a 32 deg \times 32 deg region around A3558 (see Figure 2 of Raychaudhury et al.1991), also indicates an alignment of all major clusters in the Hydra-Centaurus region spanning from position angles of 40 deg to 60 deg. Considering the physical dimensions involved, it is quite surprising that the average alignment of major clusters in the Shapley Concentration is consistent with the direction of alignment of several substructures within A3558 and with the major axis position angle of its dominant galaxy. We find that these small to large scale coincidental associations (namely, cD major axis match to the general clustering alignment) can be taken as an observational evidence of an anisotropic merger scenario as for instance the one proposed by West (1994a). (Page 16 of my paper).
I cannot tell you now whether such an alignment coincides with the Axis. It has been a long time since I was directly involved with studying clusters of galaxies.
Best,
Christine