Shapes of one million galaxies hint at the universe’s origins

A recent study published in the journal Physical Review D marks a significant advancement in cosmology. A team of researchers has analyzed over one million galaxies to delve into the origins of the universe’s current cosmic structures. 

This study contributes to the understanding of the ΛCDM model, the standard framework for the universe, which posits the significance of cold dark matter (CDM) and dark energy (the cosmological constant, Λ).

Primordial fluctuations 

The model theorizes that primordial fluctuations, originating at the universe’s inception, acted as catalysts for the formation of all celestial objects, including stars, galaxies, and galaxy clusters. 

These fluctuations, initially small, grew over time due to gravitational forces, eventually forming dense regions of dark matter, or halos. These halos then collided and merged, leading to the creation of galaxies.

Spatial distribution of galaxies

The spatial distribution of galaxies, significantly influenced by these primordial fluctuations, has been a key focus for researchers. 

In addition to this, the galaxy shapes distributed across the universe also reflect these primordial fluctuations. Traditional analysis, however, has primarily centered on the spatial distribution of galaxies as points.

Focus of the study 

The research was led by Toshiki Kurita, a graduate student at the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) at the time of the study (now a postdoctoral researcher at the Max Planck Institute for Astrophysics), and Kavli IPMU Professor Masahiro Takada.

The team developed a novel method to measure the power spectrum of galaxy shapes. This method combines spectroscopic data of galaxies’ spatial distribution with imaging data of individual galaxy shapes.

Critical new insights 

By analyzing approximately one million galaxies from the Sloan Digital Sky Survey (SDSS), the team successfully constrained the statistical properties of the primordial fluctuations that seeded the formation of the universe’s structure.

The experts discovered a significant alignment in the orientations of galaxies’ shapes, even over distances exceeding 100 million light years, suggesting correlations between distant galaxies whose formation processes are seemingly independent.

“In this research, we were able to impose constraints on the properties of the primordial fluctuations through statistical analysis of the ‘shapes’ of numerous galaxies obtained from the large-scale structure data,” Kurita said. 

“There are few precedents for research that use galaxy shapes to explore the physics of the early universe, and the research process, from the construction of the idea and development of analysis methods to the actual data analysis, was a series of trial and error.”

Wonderful research achievement

The study also confirmed that the observed correlations are consistent with those predicted by inflation theory and do not exhibit a non-Gaussian feature of the primordial fluctuation. 

Takada, expressing pride in Kurita’s work, said: “This research is the result of Toshiki’s doctoral dissertation. It’s a wonderful research achievement in which we developed a method to validate a cosmological model using galaxy shapes and galaxy distributions, applied it to data, and then tested the physics of inflation.”

The research sets a foundation for future studies to further test inflation theory, potentially opening new avenues in cosmological research and deepening our understanding of the universe’s origins and evolution.

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