Groundbreaking observations reveal variations in dark matter below the scale of galaxies, confirming the theory of cold dark matter and providing new insights into the composition of the universe.
A research team led by Professor Kitaro Inoue of Kinki University in Osaka Prefecture is using the Atacama Large Millimeter/Submillimeter Array, the world’s most powerful radio interferometer, to study the universe on a scale smaller than massive galaxies. We discovered fluctuations in the dark matter distribution.alma telescope), located in the Republic of Chile.
This is the first time that spatial fluctuations in dark matter in the distant Universe have been detected on a scale of 30,000 light years. This result indicates the existence of cold dark matter.[1] is also favored on scales smaller than massive galaxies, making it an important step toward understanding the true nature of dark matter.The article will be published in of astrophysical journal.
Key Point
- Observation by ALMA, one of the world’s largest radio interferometers, which is an international project.
- First detection of fluctuations in dark matter in the universe on a scale of less than 30,000 light years.
- An important step towards elucidating the true nature of dark matter.
ALMA detects small-scale fluctuations in dark matter distribution
Dark matter, an invisible substance that makes up most of the mass of the universe, is thought to have played an important role in the formation of structures such as stars and galaxies.[2] Because dark matter is not evenly distributed in the universe, but in clumps, its gravity can slightly change the path of light (including radio waves) coming from distant sources. . Observations of this effect (gravitational lensing) have shown that dark matter is associated with relatively large galaxies and galaxy clusters, but it remains unclear how dark matter is distributed on smaller scales. I don’t understand.
The research team decided to use ALMA to observe celestial objects located 11 billion light years from Earth. This object is a quasar with lenses,[3] MG J0414+0534[4] (Hereinafter referred to as “this quasar.”)
This quasar appears as a quadruple image due to the gravitational lensing of the foreground galaxy. However, the position and shape of these apparent images are different from those calculated only from the gravitational lensing effect of the foreground galaxy, and the gravitational lensing effect of the dark matter distribution on a scale smaller than that of the massive galaxy is at work. is shown.
It was found that there is spatial variation in the density of dark matter even on a scale of approximately 30,000 light years, which is far below the cosmic scale (tens of billions of light years). This result is consistent with cold dark matter theoretical predictions, which predict that clumps of dark matter exist not only within galaxies (light yellow in Figure 2) but also in intergalactic space (orange in Figure 2). Masu.
The gravitational lensing effect caused by the dark matter clumps found in this study is extremely small, making it extremely difficult to detect on its own. But thanks to the gravitational lensing effect caused by the foreground galaxy and ALMA’s high resolution, we were able to detect the effect for the first time. Therefore, this research is an important step in validating the theory of dark matter and elucidating its true nature.
This research was published in the paper “ALMA Measurement of 10 kpc-scale Lensing Power Spectra according to the Lensed Quasar MG J0414+0534” by KT Inoue et al.inside astrophysical journal.
Note
- cold dark matter
As the universe expands, the density of matter decreases, so particles of dark matter (matter invisible to light) no longer encounter other particles and begin to move independently from the normal motion of matter. Become. In this case, dark matter particles that move at a speed much slower than the speed of light relative to normal matter are called cold dark matter. Due to its slow speed, it does not have the ability to erase the large-scale structure of the universe. - Structure formation of the universe
In the early Universe, stars and galaxies are thought to have formed through the gravitational growth of dark matter density fluctuations and the aggregation of hydrogen and helium attracted to clumps of dark matter. The distribution of dark matter at scales smaller than massive galaxies is still unknown. - quasar
Quasars are compact regions at the center of galaxies that emit extremely bright light. There is a large amount of dust that emits radio waves in and around the dense area. - MG J0414+0534
MG J0414+0534 is located in the direction of Taurus as seen from Earth. This object’s redshift (the increase in wavelength of light divided by the original wavelength) is z=2.639. Taking into account the uncertainties in the cosmological parameters, the corresponding distance is assumed to be 11 billion light-years.
Reference: “ALMA measurement of 10 kpc scale lens power spectrum for lensed quasar MG J0414+0534”, Kaiki Taro Moeno, Takeo Minezaki, Satokimatsushita, Kouicular Middleishi, September 7, 2023. astrophysical journal.
DOI: 10.3847/1538-4357/aceb5f
This research was supported by the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (Project Numbers 17H02868 and 19K03937), the National Astronomical Observatory of Japan ALMA Joint Scientific Research Project 2018-07A, and the ALMA Japan Research Grant. National Astronomical Observatory of Japan-ALMA-256 Fund, and Taiwan MoST 103-2112-M-001-032-MY3, 106-2112-M-001-011, 107-2119-M-001-020, 107-2119-M-001 – 020.