This Thursday (20:10 UK time) astronomy twitter journal club is tackling a paper that may have major implications for cosmology if the results it presents are correct: Detection of a Dipole in the Handedness of Spiral Galaxies with Redshifts z ~ 0.04 by Michael Longo. As the paper’s introduction states:
A basic assumption of essentially all cosmological models and general relativity is the “Cosmological Principle” that over large enough distance scales the Universe is homogeneous and isotropic. This paper presents strong evidence for a parity-violating special axis as demonstrated by a dipole in the distribution of spiral galaxy handedness for redshifts < 0.085.
On the smallest scales, a parity violating asymmetry was found in the angular distribution of electrons in the beta spin decay of spin orientated 60Co…On the molecular scale, there is a large predominance of left-handed amino acids over right-handed ones in organisms…It is reasonable to ask if nature exhibits such an asymmetry on the largest scales.
The method used is very simple – take a sample of local spiral galaxies from the Sloan Digital Sky Survey, classify them based on their direction of rotation (taking into account any biases you think are present) and then examine the results to see if there’s a preferred direction of spin.
This paper repeats, and confirms, earlier work by the same author using a smaller sample of galaxies. However, other work, such as this 2008 paper from the Galaxy Zoo team, find no significant evidence for a preferred handedness.
A preference for spiral galaxies in one sector of the sky to be left-handed or right-handed spirals would indicate a parity violating asymmetry in the overall universe and a preferred axis. This study uses 15158 spiral galaxies with redshifts <0.085 from the Sloan Digital Sky Survey. An unbinned analysis for a dipole component that made no prior assumptions for the dipole axis gives a dipole asymmetry of -0.0408 +/- 0.011 with a probability of occurring by chance of 7.9 x 10^-4. A similar asymmetry is seen in the Southern Galaxy spin catalog of Iye and Sugai. The axis of the dipole asymmetry lies at approx. (l, b) =(52deg, 68.5deg), roughly along that of our Galaxy and close to alignments observed in the WMAP cosmic microwave background distributions. The observed spin correlation extends out to separations ~210 Mpc/h, while spirals with separations < 20 Mpc/h have smaller spin correlations.