Patterns of galaxy spin directions in SDSS and Pan-STARRS show parity violation and multipoles
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ORIGINAL ARTICLE
Patterns of galaxy spin directions in SDSS and Pan-STARRS show parity violation and multipoles Lior Shamir1
Received: 11 June 2020 / Accepted: 31 July 2020 © Springer Nature B.V. 2020
Abstract The distribution of spin directions of ∼ 6.4 · 104 SDSS spiral galaxies with spectra was examined, and compared to the distribution of ∼ 3.3 · 104 Pan-STARRS galaxies. The analysis shows a statistically significant asymmetry between the number of SDSS galaxies with opposite spin directions, and the magnitude and direction of the asymmetry changes with the direction of observation and with the redshift. The redshift dependence shows that the distribution of the spin direction of SDSS galaxies becomes more asymmetric as the redshift gets higher. Fitting the distribution of the galaxy spin directions to a quadrupole alignment provides fitness with statistical significance > 5σ , which grows to > 8σ when just galaxies with z > 0.15 are used. Similar analysis with Pan-STARRS galaxies provides dipole and quadrupole alignments nearly identical to the analysis of SDSS galaxies, showing that the source of the asymmetry is not necessarily a certain unknown flaw in a specific telescope system. While these observations are clearly provocative, there is no known error that could exhibit itself in such form. The data analysis process is fully automatic, and uses deterministic and symmetric algorithms with defined rules. It does not involve either manual analysis that can lead to human perceptual bias, or machine learning that can capture human biases or other subtle differences that are difficult to identify due to the complex nature of machine learning processes. Also, an error in the galaxy annotation process is expected to show consistent bias in all parts of the sky, rather than change with the direction of observation to form a clear and definable pattern. Keywords Spiral galaxies · Large-scale structure
B L. Shamir
[email protected]
1
Kansas State University, Manhattan, KS 66502, USA
1 Introduction Spiral galaxies are unique astronomical objects in the sense that their visual appearance depends on the perspective of the observer. Since the spin patterns of spiral galaxies (clockwise or counterclockwise) are expected to be randomly distributed, in a sufficiently large universe no difference between clockwise and counterclockwise galaxies is expected. However, analysis of large datasets of spiral galaxies showed photometric differences between spiral galaxies with clockwise spin patterns and spiral galaxies with counterclockwise spin patterns (Shamir 2013, 2016b, 2017a,c,b, 2020a). Early attempts to identify differences between clockwise and counterclockwise galaxies did not identify statistically significant asymmetry (Iye and Sugai 1991; Land et al. 2008). However, these experiments were based on much smaller datasets of just a few thousand galaxies (Iye and Sugai 1991), or on heavily biased manual classification performed by untrained volunteers (Land et al. 2008). Experiments using manually annotated galaxies
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