Researchers Use Data from Over One Million Galaxies to Gain Fresh Insights into the Origin of the Universe

Researchers have carried out an in-depth examination of more than a million galaxies to delve into the origins of the cosmos's composition, unveiling noticeable arrangements in galaxy forms across massive distances. This study, which made use of new strategies and corroborated facets of inflation theory, signifies a substantial stride in comprehending how the universe formed.

A group of scientists meticulously analysed over a million galaxies, aiming to unravel the beginnings of modern cosmic structures, according to a recently issued paper featured as an Editor's Suggestion in Physical Review D.

Up until this point, scrupulous investigations and assessments of the cosmic microwave background (CMB) and large-scale structure (LSS) have led to the creation of the standard universe model, commonly known as the ΛCDM model. Within this model, cold dark matter (CDM) and dark energy (the cosmological constant, Λ) are key attributes.

An image derived from observing the universe's large-scale structure showcases numerous objects coloured yellow to red that represent galaxies hundreds of millions of light years from Earth. These galaxies display a wide variety of attributes and are too countless in the immensity of space to quantify. The pattern and spatial arrangement of these galaxies is not haphazard, but instead contain “correlations” that stem from statistical attributes of the initial primordial fluctuations as anticipated by inflation.

The model posits that primordial fluctuations were created in the early stages of the universe and functioned as catalysts, initiating the creation of everything within the universe including stars, galaxies, galaxy clusters, and their spatial dispersion in space. These variations initiate as minuscule but evolve over time due to gravitational attraction, ultimately compounding to create a dense region of dark matter or a halo. Then, these halos continuously clashed and amalgamated, which led to the creation of celestial entities such as galaxies.

The characteristics of the spatial arrangement of galaxies are largely moulded by the properties of the original primary fluctuations that induced their creation. As such, the statistical analysis of galaxy distributions has been extensively utilized to inspect the underlying primitive fluctuations observable in nature. Furthermore, the spatial configuration of galaxy forms extending over broad areas of the universe also discloses the characteristics of the intrinsic primary fluctuations.

The conventional approach to analysing large-scale structure has solely focused on galaxies' spatial dispersion as points. More recently, however, the scientific community has begun exploring galaxy shapes as they not only yield additional information but also offer a fresh perspective on the attributes of primitive fluctuations.

An examination of how distinct primordial fluctuations of the universe contribute to the different spatial arrangement of dark matter has been visualized. The central figure displays the fluctuations in the standard Gaussian distribution, with color variations ranging from blue to yellow representing the value of the fluctuation at the said location, from areas with low to high density. Other figures show slight deviations from the Gaussian distribution which are termed non-Gaussian. These images demonstrate isotropic and anisotropic non-Gaussianity and can be used in the search for anisotropic non-Gaussianity from the spatial pattern of galaxy shapes.

A group of scientists led by then-graduate student Toshiki Kurita of the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) (now a postdoctoral researcher at the Max Planck Institute for Astrophysics), and Kavli IPMU Professor Masahiro Takada contrived a method to quantify the power spectrum of galaxy shapes. This strategy extracts key statistical data from galaxy shape configurations by integrating the spectroscopic data of spatial galaxy distribution with imaging data of individual galaxy forms.

The researchers simultaneously analyzed the spatial distribution and shape pattern of approximately one million galaxies from the Sloan Digital Sky Survey (SDSS), the world’s largest survey of galaxies today.

As a result, they successfully constrained statistical properties of the primordial fluctuations that seeded the formation of the structure of the entire universe.

The blue dots and error bars are the values of the galaxy shape power spectrum. The vertical axis corresponds to the strength of correlation between two galaxy shapes, i.e., the alignment of the galaxy shape orientations. The horizontal axis represents the distance between two galaxies, with the left (right) axis representing the correlation between more distant (closer) galaxies. The gray dots indicate non-physical apparent correlations. The fact that this value is zero within error, as expected, confirms that the blue measured points are indeed astrophysically-origined signals. The black curve is the theoretical curve from the most standard inflationary model, and it is found to be in good agreement with the actual data points. Credit: Kurita & Takada

They found a statistically significant alignment of the orientations of two galaxies’ shapes more than 100 million light-years apart. Their result showed correlations exist between distant galaxies whose formation processes are apparently independent and causally unrelated.

“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 Kurita.

Furthermore, a detailed investigation of these correlations confirmed they are consistent with the correlations predicted by inflation, and do not exhibit a non-Gaussian feature of the primordial fluctuation.

“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. It was a research topic that no one had ever done before, but he did all three steps: theory, measurement, and application. Congratulations! I am very proud of the fact that we were able to do all three steps. Unfortunately, I did not make the great discovery of detecting a new physics of inflation, but we have set a path for future research. We can expect to open up further areas of research using the Subaru Prime Focus Spectrograph,” said Takada.

The methods and results of this study will allow researchers in the future to further test inflation theory.