According to a study published in Physical Review Letters, a team led by a Tokyo Metropolitan University member has made progress in the search for dark matter by examining galaxies using new spectrographic technology and the Magellan Clay Telescope.
Spectrographic technology to separate light from decaying dark matter and background light. WINERED uses the broader spectral properties of background light to tell it apart from light from decay events. Image Credit: Wen Yin, Tokyo Metropolitan University
With only 4 hours of observations, precise infrared measurements have established new limitations on the lifetime of dark matter. Their findings underscore the critical utility of their technique and broaden the search to hitherto unexplored areas of the spectrum.
Over the last century, cosmologists have struggled with an apparent discrepancy in their observations of the cosmos. Observations of galaxies’ spin, for example, imply that there is far more mass than we can perceive. Physicists have referred to this “missing” mass as “dark matter.” The quest for dark matter is extremely challenging because it is not visible and have no notion of what to look for.
Now, researchers are using a combination of simulations and cutting-edge observations to constrain the features of dark matter. In a recent advance, a team of Japanese scientists led by Associate Professor Wen Yin from Tokyo Metropolitan University employed a novel spectrographic approach to study light from two galaxies, Leo V and Tucana II. They collected light arriving on Earth using Chile’s 6.5-meter-wide Magellan Clay Telescope, focusing on the infrared area of the spectrum.
The team concentrated on a promising dark matter candidate, the axionlike particle (ALP), and studied how it “decays” and spontaneously emits light. Leading theoretical models indicate that the near-infrared region of the spectrum is a highly intriguing area to investigate. However, the infrared spectrum is dense and perplexing.
This is due to the wide spectrum of noise and interference from various sources. Examples include zodiacal light, the faint scattering of sunlight by interstellar dust, and the light emitted by the atmosphere when heated by the sun.
To address this, they previously presented a new technique that takes advantage of the fact that background radiation has a greater range of wavelengths, whereas light from a single decay process is more strongly skewed to a small range. Just like light viewing from a prism dims as distinct hues are spread thinner and thinner, decay events within a narrow range get sharper and sharper.
This approach can be used on a variety of state-of-the-art infrared spectrographs, including NIRSpec on the James Webb Space Telescope, WINERED on the Magellan Clay Telescope, and many others, effectively transforming these instruments into excellent dark matter detectors.
The team was able to account for all of the light they saw in the near infrared to a significant statistical accuracy because of the accuracy of their technique (WINERED). The absence of decay was then utilized to establish a lower bound on the lifespan of ALP particles or upper bounds on the frequency of these decay events. Ten to a hundred million times the universe’s age, or ten to twenty-six zeros after it, is their new lower bound in seconds.
The discovery is remarkable not only because it establishes the most restrictive limit for the lifetime of dark matter. The work applies cutting-edge infrared cosmology technologies to fundamental particle physics challenges. While their results are based on rigorous examination of the data so far, there are hints of abnormalities or “excesses” that raise the tantalizing prospect of genuine dark matter detection with more data and study. The search continues for the missing component of the universe.
This study was supported by JSPS KAKENHI Grant Numbers 22K14029, 20H05851, 21K20364, and 22H01215, as well as Tokyo Metropolitan University's Incentive Research Fund for Young Researchers. The 6.5-m Magellan Clay Telescope at Las Campanas Observatory in Chile was used to collect WINERED data under the proposal “eV-Dark Matter search with WINERED.”
The University of Tokyo and Kyoto Sangyo University’s Laboratory of Infrared High-resolution Spectroscopy developed WINERED with funding from JSPS KAKENHI Grant Numbers 16684001, 20340042, and 21840052, as well as the MEXT Supported Program for the Strategic Research Foundation at Private Universities (Nos. S0801061 and S1411028).
The observing runs in June 2023 and November 2023 were partially funded by JSPS KAKENHI Grant Number 19KK0080, JSPS Bilateral Program Number JPJSBP120239909, and Project Research Number AB0518 from the Astrobiology Center at NINS, Japan.
Journal Reference:
Yin, W. et. al. (2025) First Result for Dark Matter Search by WINERED. Physical Review Letters. doi.org/10.1103/PhysRevLett.134.051004