"Physical Review D" published a latest research report in the form of "Editors' Suggestion". The report stated that a research team analyzed more than 1 million galaxies to explore the origin of the structure of the present universe. Researchers have revealed a remarkable arrangement of galaxy shapes over vast distances, using an innovative approach that confirms aspects of inflation theory and marks significant progress in understanding the formation of the universe.

Until today, precise observations and analysis of the cosmic microwave background (CMB) and large-scale structure (LSS) have established a standard framework of the universe, the so-called ΛCDM model, in which cold dark matter (CDM) and dark energy (cosmological constant Λ) are important features.

Images obtained by observing the large-scale structure of the universe. The numerous objects shown from yellow to red represent galaxies hundreds of millions of light-years away from Earth. These galaxies come in a variety of colors and shapes and are countless in the vastness of space. The spatial distribution and shape patterns of these galaxies are not random, but have "correlations" derived from the statistical properties of the original fluctuation seeds predicted by inflation. Source: SubaruHSC

This model believes that the original wave was generated at the beginning of the universe, or in the early days of the universe. It was like a trigger, leading to the creation of everything in the universe, including stars, galaxies, galaxy clusters, and their spatial distribution throughout space. Although the fluctuations are very small when they are generated, over time, the fluctuations will continue to increase under the pull of gravity, eventually forming a dense area of ​​dark matter, which is the halo. Then, different rings collided repeatedly and merged with each other, forming celestial objects such as galaxies.

Galaxy distribution and original fluctuations

Since the nature of the spatial distribution of galaxies is deeply affected by the nature of the original fluctuations that originally produced the galaxies, people have been actively conducting statistical analyzes on the distribution of galaxies in order to explore the nature of the original fluctuations observationally. In addition to this, spatial patterns in the shapes of galaxies spread across vast areas of the universe also reflect the nature of the underlying primordial fluctuations.

However, traditional large-scale structural analysis only focuses on the spatial distribution of galaxies as points. Recently, researchers have begun studying the shape of galaxies because it not only provides more information, but also reveals the nature of the original fluctuations from another perspective.

A visual diagram of how "differences" in the original fluctuations of the universe lead to different spatial distributions of dark matter. The center plot (shared by the upper and lower rows) shows fluctuations in a reference Gaussian distribution. The color gradient (from blue to yellow) corresponds to the fluctuating values ​​at that location (from a low-density area to a high-density area). The images on the left and right show fluctuations that deviate slightly from a Gaussian or non-Gaussian distribution. The sign in parentheses indicates the sign of the deviation from the Gaussian distribution, with negative (-) deviations on the left and positive (+) deviations on the right. The top row is an example of isotropic non-Gaussian. Compared to the central Gaussian fluctuations, the left image shows an increase in areas of large negative values ​​(dark blue), while the image on the right shows an increase in areas of large positive values ​​(bright yellow). It is known that we can use the observed spatial distribution of galaxies to look for this isotropic non-Gaussianity. The figure below is an example of anisotropic non-Gaussianity. Compared to the isotropic case in the upper image, the overall brightness and darkness are unchanged compared to the Gaussian fluctuations in the middle image, but the shape of each region is. We can look for this "anisotropic" non-Gaussian nature in the spatial patterns of galaxy shapes. Source: Kurita & Takada

A research team led by then Kavli IPMU graduate student Toshiki Kurita (now a postdoctoral fellow at the Max Planck Institute for Astrophysics) and Kavli IPMU Professor Masahiro Takada developed a method to measure the power spectrum of galaxy shapes to extract key statistical information from galaxy shape patterns by combining spectral data on the spatial distribution of galaxies and imaging data on individual galaxy shapes.

Comprehensive analysis and key findings

The researchers also analyzed the spatial distribution and shape patterns of about 1 million galaxies from the Sloan Digital Sky Survey (SDSS), the largest galaxy survey in the world today.

Thus, they succeeded in constraining the statistical properties of the original fluctuations from which the entire structure of the universe was formed.

The blue dots and error bars are numerical values ​​for the galaxy shape power spectrum. The vertical axis represents the strength of the correlation between the shapes of two galaxies, that is, the consistency of the direction of the galaxy shapes. The horizontal axis represents the distance between two galaxies, and the left (right) axis represents the correlation between more distant (nearer) galaxies. Gray dots represent non-physical apparent correlations. The value is zero within the error margin, which confirms that the blue measurement point is indeed an astrophysically generated signal. The black curve is the theoretical curve of the most standard inflation model and matches the actual data points very well. Source: Kurita&Takada

They found that there was a statistically significant consistency in the shape and orientation of the two galaxies more than 100 million light-years apart. Their results show that there are correlations between distant galaxies that apparently formed independently and without cause-and-effect relationships.

"In this study, we imposed constraints on the properties of the original waves through statistical analysis of the 'shapes' of numerous galaxies obtained from large-scale structural data. There is little precedent for using galaxy shapes to explore the physics of the early universe, and the research process was a series of trial and error, from conception and development of analytical methods to actual data analysis. Because of this, I faced many challenges. But I am glad that I was able to complete these tasks during my PhD. I believe that this result will be the first step in using galaxy shapes to open up a new research field in cosmology."

Furthermore, a detailed study of these correlations confirms that they are consistent with those predicted by inflation and do not exhibit the non-Gaussian characteristics of the original fluctuations.

"This research is the result of Toshiki's doctoral thesis. It is a remarkable research result. We developed a method to validate a cosmological model using the shape and distribution of galaxies, applied it to the data, and then tested the physics of inflation. This is an unprecedented research topic, but he completed the theory, measurement and application of this Three steps. Congratulations! I'm very proud that we were able to complete all three steps. Unfortunately, I didn't make this great discovery of new inflation physics, but we have opened up a path for future research with the Subaru Prime Focus Spectrograph," said Takada.

Compiled source: ScitechDaily