Friday, June 9, 2023

Galactic alignment millions of light-years away support general relativity

Dark order in the universe.

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The origin of the accelerating expansion of the universe, namely, dark energy or/and modification of Einstein’s gravity theory, is still a complete mystery in fundamental physics. Hence, deeper and wider galaxy surveys are ongoing better to understand the expansion and growth history of the universe.

Researchers from several worldwide institutions, including Kyoto University, have verified that the inherent alignments of galaxies possess properties that make them an effective tool for probing dark matter and energy on a cosmic scale.

The team tested the general theory of gravity at enormous spatial scales by accumulating evidence that the distribution of galaxies more than tens of millions of light years away is subject to the gravitational effects of dark matter. The 1.2 million archival galaxy observations provided the data that the worldwide team used to analyze the locations and orientations of galaxies. The subsequent statistical analysis quantified the degree to which the orientation of distant galaxies is aligned using the 3D positional data of each galaxy that was available.

Lead author, Atsushi Taruya of KyotoU’s Yukawa Institute for Theoretical Physics, said, “These alignments, which are primarily produced by interactions with nearby objects, have been regarded as systematic noise in measuring weak lensing effect.”

Teppei Okumura of the Academia Sinica Institute of Astronomy and Astrophysics said, “We have also successfully measured the rate at which the galaxy distribution gradually becomes denser due to gravity, which is consistent with the general theory of relativity.”

“Our research verified general relativity at the distant universe, but the nature of dark energy or the origin of cosmic acceleration remains unresolved.”

The achieved data involves three galaxy samples selected for their brightness and distance. The magnitude of alignment in relation to distant galaxies was also measured using 3D locations and shape data for each galaxy.

The team’s model’s outcomes supported theoretical predictions. They provided Taruya and Okumura with compelling proof that these galaxies’ orientations are connected, bolstering the case for general relativity on a cosmological scale.

Taruya said“Current endeavors, such as the Subaru Telescope project, will provide extremely high-quality, high-precision observational data. These will spearhead innovative cosmological research using the intrinsic alignments to shed light on the nature of dark energy.”

Journal Reference:

  1. Teppei Okumura and Atsushi Taruya. First Constraints on Growth Rate from Redshift-space Ellipticity Correlations of SDSS Galaxies at 0.16 < z < 0.70. The Astrophysical Journal Letters. DOI 10.3847/2041-8213/acbf48
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