An international team of scientists used advanced techniques and Hyper Suprime-Cam to study the “clumpiness” of dark matter and found an S8 value of 0.76, which contrasts with the cosmic microwave background value of 0.83. This inconsistency may indicate measurement errors or an incomplete Standard Cosmological Model.

An international group of astrophysicists and cosmologists from various institutes, including the Kavli Institute for Physics and Mathematics of the Universe (Kavli IPMU), presented a five-article series measuring the value of the “mass” of the dark matter of the universe. as cosmologists S₈, 0.76, is consistent with values ​​found by other gravitational lensing studies looking at the relatively new universe, but inconsistent with the value 0.83 obtained from the cosmic microwave background, which dates back to the origin of the universe. The universe was about 380 years old. 000 years. The results have been uploaded as preprint papers to: arXiv.

The difference between these two values ​​is small, but this does not seem like a coincidence as more and more studies support each of the two values. Perhaps there is an as yet unrecognized error in one of these two measurements, or the standard cosmological model is curiously incomplete.

Dark energy and dark matter make up 95% of our universe we see today, but we know very little about what they really are and how they have evolved over the history of the universe. Clumps of dark matter distort the light of distant galaxies through weak gravitational lensing, a phenomenon predicted by Einstein’s General Theory of Relativity.

“This distortion is a very, very small effect. The shape of a single galaxy has been imperceptibly distorted. But combining measurements for millions of galaxies allows us to measure the distortion with extremely high precision,” he said.

The standard model is defined by just a few numbers: the rate of expansion of the universe, a measure of how bulky dark matter is, and the relative contribution of the components of the universe (matter, dark matter, and dark matter). energy), a technical quantity that describes the total density of the universe and how the lumpiness of the universe at large scales relates to that at small scales.

Cosmologists try to test this model by restricting it in various ways, such as observing fluctuations in the cosmic microwave background, modeling the expansion history of the universe, or measuring the complexity of the universe in the relatively recent past.

A team led by astronomers from Kavli IPMU, the University of Tokyo, Nagoya University, Princeton University and the astronomical societies of Japan and Taiwan spent the last year solving the mysteries of this elusive matter, dark matter, using sophisticated computer simulations. and data from the first three years of the Hyper Suprime-Cam operation. For this study, the observations used Hyper Suprime-Cam (HSC), one of the most powerful astronomical cameras in the world, mounted on the Subaru Telescope atop Maunakea in Hawaii.

Data hiding and disclosure

The team did a “blind analysis”.

“Scientists are human and have preferences. Some really want to find something fundamentally new, while others may feel comfortable finding results that seem consistent with expected results. Nagoya University’s Kobayashi-Maskawa Origin Institute states, “No matter how careful scientists are, They are self-aware enough to know that if they do not conduct their analysis without knowing the results, they will bias themselves,” said Hironao Miyatake, Associate Professor of Particles and Universe (KMI).

To protect the results from such bias, the HSC team hid their results from themselves and their colleagues for months. The team even added an extra layer of obfuscation: they analyzed three different catalogs of galaxies, one real and two fakes, with numerical values ​​offset by random values. The analysis team didn’t know which one was real, so even if someone saw the value, they didn’t know if the results were based on the real catalog.

The team spent a year doing the blind analysis. On December 3, 2022, the team gathered on Zoom for “revealing” on a Saturday morning in Japan and on a Friday evening in Princeton. According to Takada, the team published the data and ran their graphs and immediately saw that it was great. “Blind analysis means you can’t keep an eye on the results while running the analysis, which is extremely stressful, but when I saw the final result, all my worries vanished,” said Kavli IPMU graduate student Sunao. sugiyama

An example of the three-dimensional distribution of dark matter obtained with the HSC-SSP. This map was created using data from the first year, but the current study examined an area of ​​the sky about three times larger than that. Credit: University of Tokyo/NAOJ

Giant research with the world’s largest telescope camera

The HSC is the largest camera on a telescope of its size in the world. The survey used by the research team covers about 420 square degrees of the sky, roughly equivalent to 2,000 full moons. It is not a contiguous piece of heaven, but divided into six different parts, each the size of an outstretched human fist. The 25 million galaxies the researchers studied are so distant that instead of seeing them as they are today, HSC recorded them billions of years ago.

Each of these galaxies glows with the fire of tens of billions of suns, but because they are so far away they are extremely faint, 25 million times dimmer than the faintest stars we can see with the naked eye. Source