Figure 1: Example of an image acquired with HSC-SSP. Credit: HSC-SSP & NAOJ Project
The astrophysicists found the dark matter “roughness” of the universe to be 0.76, a number that contradicts the cosmic microwave background value of 0.83, indicating possible errors or an incomplete cosmological model. The study uses data from Subaru’s strategic Hyper Suprime-Cam program and will further investigate this compelling discrepancy.
An international team of astrophysicists and cosmologists at various institutes, including NAOJ and the Kavli Institute for the Physics and Mathematics of the Universe, presented a set of five papers measuring the value for the “density” of the universe’s dark matter, known to cosmologists as C8. The reported value is 0.76, which matches values that other gravitational lensing studies have found looking at the relatively recent Universe – but does not match the value of 0.83 obtained from the cosmic microwave background, which dates back to when the Universe was was about 380,000 years old. The difference between these two values is small, but does not appear to be random. The possibilities are that there is some as-yet-unrecognized error or error in one of these two measurements, or that the Standard Cosmological Model is incomplete in some interesting way.
The Standard Model of our universe is defined by just a few numbers: the expansion rate of the universe, a measure of how lumpy dark matter is (S8), the relative contributions of the universe’s constituents (matter, dark matter, and dark energy), the total density of the universe, and a technical quantity describing how the bulkiness of the universe on large scales is related to that on small scales. Cosmologists are eager to test this model by constraining these numbers in various ways, such as by observing fluctuations in the cosmic microwave background, modeling the expansion history of the universe, or measuring the clumpiness of the universe in the relatively recent past.
Figure 2: Example of a 3D dark matter distribution obtained by HSC-SSP. That map was produced using data from the first year, but the current study examines an area of the sky about three times larger than that. Credit: University of Tokyo/NAOJ
A team led by astronomers from the Kavli IPMU, University of Tokyo, Nagoya University, Princeton Universityand the astronomical communities of Japan and Taiwan have spent the past year unlocking the secrets of that most elusive material, dark matter, using sophisticated computer simulations and data from the first three years of the strategic Hyper Suprime-Cam Subaru (HSC-SSP) program. The observing program uses one of the world’s most powerful astronomical cameras, the Hyper Suprime-Cam (HSC), mounted on the Subaru Telescope. The HSC-SSP data the research team used covers about 420 square degrees of the sky, which is equivalent to 2,000 full moons.
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 really small effect; the shape of a galaxy is distorted by a imperceptible amount. But the team measured the distortion with fairly high precision by combining measurements for 25 million faint galaxies that are billions of light-years away. The team then measured the clumpiness of the universe today (Figure 3).
Figure 3: Measurement results of the S8 parameter from the HSC-SSP year 3 data. The chart shows the results of four different methods that use different parts of the HSC-SSP Year 3 data or combine the HSC-SSP Year 3 data with other data. For comparison, “Planck CMB” shows the measurement result for S8 from the cosmic microwave background data from the Planck satellite. “Other weak lensing results” shows the results of similar weak lensing measurements based on data from the Dark Energy Survey (DES) and the Kilodegree Survey (KiDS). Credit: Kavli IPMU
The discrepancy between S8 values of HSC-SSP and the Planck satellite is very fine. The team believes that the measurement was done correctly and carefully. And the statistics show that there is only a one in 20 chance that the difference is due to chance alone, which is convincing but not entirely conclusive. The team will continue to pursue this compelling discrepancy using the full HSC-SSP dataset and advanced methods. The team may discover something new about the universe, so please stay tuned.
For more information on this research, see Measuring dark matter with the Hyper Suprime-Cam reveals a discrepancy.
References:
“Hyper Suprime-Cam Year 3 Results: Galaxy Clustering and Weak Lensing Cosmology with HSC and SDSS” by Hironao Miyatake, Sunao Sugiyama, Masahiro Takada, Takahiro Nishimichi, Xiangchong Li, Masato Shirasaki, Surhud More, Yosuke Kobayashi, Atsushi J . Nishizawa, Markus M. Rau, Tianqing Zhang, Ryuichi Takahashi, Roohi Dalal, Rachel Mandelbaum, Michael A. Strauss, Takashi Hamana, Masamune Oguri, Ken Osato, Wentao Luo, Arun Kannawadi, Bau-Ching Hsieh, Robert Armstrong, Yutaka Komiyama, Robert H. Lupton, Nate B. Lust, Lauren A. MacArthur, Satoshi Miyazaki, Hitoshi Murayama, Yuki Okura, Paul A. Price, Tomomi Sunayama, Philip J. Tait, Masayuki Tanaka, and Shiang-Yu Wang April 3, 2023, Astrophysics > Cosmology and Non-Galactic Astrophysics.
arXiv: 2304.00704
“Hyper Suprime-Cam Year 3 Results: Measurements of SDSS-BOSS Galaxy Clustering, Galaxy-Galaxy Lensing, and Cosmic Shear” by Surhud More, Sunao Sugiyama, Hironao Miyatake, Markus Michael Rau, Masato Shirasaki, Xiangchong Li, Atsushi J Nishizawa, Ken Osato, Tianqing Zhang, Masahiro Takada, Takashi Hamana, Ryuichi Takahashi, Roohi Dalal, Rachel Mandelbaum, Michael A. Strauss, Yosuke Kobayashi, Takahiro Nishimichi, Masamune Oguri, Arun Kannawadi, Robert Armstrong, Yutaka Komiyama, Robert H. Lupton, Nate B. Lust, Satoshi Miyazaki, Hitoshi Murayama, Yuki Okura, Paul A. Price, Philip J. Tait, Masayuki Tanaka, and Shiang-Yu Wang, 3 Apr 2023, Astrophysics > Cosmology and Non-Galactic Astrophysics.
arXiv: 2304.00703
“Hyper Suprime-Cam Year 3 Results: Cosmology from Galaxy Clustering and Weak Lensing with HSC and SDSS” by Sunao Sugiyama, Hironao Miyatake, Surhud More, Xiangchong Li, Masato Shirasaki, Masahiro Takada, Yosuke Kobayashi, Ryuichi Takahashi, Takahiro Nishimichi, Atsushi J. Nishizawa, Markus M. Rau, Tianqing Zhang, Roohi Dalal, Rachel Mandelbaum, Michael A. Strauss, Takashi Hamana, Masamune Oguri, Ken Osato, Arun Kannawadi, Robert Armstrong, Yutaka Komiyama, Robert H. Lupton, Nate B. Lust , Satoshi Miyazaki, Hitoshi Murayama, Yuki Okura, Paul A. Price, Philip J. Tate, Masayuki Tanaka and Xiang-Yu Wang, 3 Apr 2023, Astrophysics > Cosmology and Non-Galactic Astrophysics.
arXiv: 2304.00705
“Hyper Suprime-Cam Year 3 Results: Cosmology from Cosmic Shear Power Spectra” by Roohi Dalal, Xiangchong Li, Andrina Nicola, Joe Zuntz, Michael A. Strauss, Sunao Sugiyama, Tianqing Zhang, Markus M. Rau, Rachel Mandelbaum, Masahiro Takada , Surhud More, Hironao Miyatake, Arun Kannawadi, Masato Shirasaki, Takanori Taniguchi, Ryuichi Takahashi, Ken Osato, Takashi Hamana, Masamune Oguri, Atsushi J. Nishizawa, Andrew A. Plazas Malagon, Tomomi Sunayama, David Alonso, Anže Slosar, Robert Armstrong , James Bosch , Yutaka Komiyama , Robert H. Lupton , Nate B. Lust , Lauren A. MacArthur , Satoshi Miyazaki , Hitoshi Murayama , Takahiro Nishimichi , Yuki Okura , Paul A. Price , Philip J. Tate, Masayuki Tanaka and Xiang-Yu Wang, 3 Apr 2023, Astrophysics > Cosmology and Non-Galactic Astrophysics.
arXiv: 2304.00701
“Hyper Suprime-Cam Year 3 Results: Cosmology from Cosmic Shear Two-Point Correlation Functions” by Xiangchong Li, Tianqing Zhang, Sunao Sugiyama, Roohi Dalal, Markus M. Rau, Rachel Mandelbaum, Masahiro Takada, Surhud More, Michael A. Strauss , Hironao Miyatake, Masato Shirasaki, Takashi Hamana, Masamune Oguri, Wentao Luo, Atsushi J. Nishizawa, Ryuichi Takahashi, Andrina Nicola, Ken Osato, Arun Kanawadi, Tomomi Sunayama, Robert Armstrong, Yutaka Komiyama, Robert H. Lupton, Nate B. Lust, Satoshi Miyazaki, Hitoshi Murayama, Takahiro Nishimichi, Yuki Okura, Paul A. Price, Philip J. Tait, Masayuki Tanaka, Shiang-Yu Wang, 3 Apr 2023, Astrophysics > Cosmology and Non-Galactic Astrophysics.
arXiv: 2304.00702
This research was supported by the National Science Foundation Graduate Fellowship Program (DGE-2039656); The National Astronomical Observatory of Japan; the Kavli Institute for Physics and Mathematics of the Universe; the University of Tokyo; The High Energy Accelerator Research Organization (KEK); the Academia Sinica Institute of Astronomy and Astrophysics in Taiwan; Princeton University; The FIRST program from the Japanese cabinet; Ministry of Education, Culture, Sports, Science and Technology (MEXT); Japan Society for the Promotion of Science; Japan Science and Technology Agency; the Toray Science Foundation; and the Vera C. Rubin Observatory.