A team of researchers has conducted a study by analysing more than one million galaxies to explore the origins of the present-day cosmic structures. The study, published in Physical Review D, aims to understand the primordial fluctuations that seeded the formation of the structure of the entire universe .
The researchers' work is based on the ΛCDM model, which is the standard framework for understanding the universe. According to this model, cold dark matter (CDM) and dark energy (the cosmological constant, Λ) are significant characteristics of the universe. The model suggests that primordial fluctuations were generated at the beginning or in the early stages of the universe. These fluctuations acted as triggers, leading to the creation of stars, galaxies, galaxy clusters, and their spatial distribution throughout space .
The spatial distribution of galaxies is strongly influenced by the nature of the primordial fluctuations that created them. Therefore, researchers have been actively conducting statistical analyses of galaxy distributions to explore the nature of these fluctuations. In addition to analyzing the spatial distribution of galaxies as points, researchers have started studying galaxy shapes to gain additional insights into the nature of primordial fluctuations .
The team of researchers developed a method to measure the power spectrum of galaxy shapes, which combines spectroscopic data of the spatial distribution of galaxies with imaging data of individual galaxy shapes. They simultaneously analyzed the spatial distribution and shape patterns of approximately one million galaxies from the Sloan Digital Sky Survey (SDSS), the world's largest survey of galaxies. Through their analysis, they successfully constrained the statistical properties of the primordial fluctuations that seeded the formation of the structure of the entire universe .
"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. There are few precedents for research that uses 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. Because of that, I faced many challenges. But I am glad that I was able to accomplish them during my doctoral program. I believe that this achievement will be the first step to open up a new research field of cosmology using galaxy shapes ," said Toshiki Kurita (currently a postdoctoral researcher at the Max Planck Institute for Astrophysic
One significant finding of the study is the statistically significant alignment of the orientations of two galaxies' shapes that are more than 100 million light years apart. This discovery indicates correlations between distant galaxies whose formation processes are apparently independent and causally unrelated. The researchers also confirmed that these correlations are consistent with the predictions of inflation, a key concept in cosmology, and do not exhibit a non-Gaussian feature of the primordial fluctuation .
The methods and results of this study provide valuable insights into the physics of the early universe and the nature of primordial fluctuations. They also open up new possibilities for future research in cosmology using galaxy shapes. The study's findings will allow researchers to further test the inflation theory and deepen our understanding of the origins of the universe .