Tokyo, Japan – A team led by a member of Tokyo Metropolitan University have made advances in the search for dark matter, observing galaxies using new spectrographic technology and the Magellan Clay Telescope. With a mere 4 hours of observations, precise measurements in the infrared range have set new limits on the lifetime of dark matter. Their findings highlight the crucial utility of their technology and extend the search to less explored parts of the spectrum.
Over the past century, cosmologists have grappled with an apparent inconsistency in what they saw in the universe. Observations of the rotation of galaxies, for example, imply that there is a lot of mass out there than we can see. Physicists have been calling this "missing" mass "dark matter." What makes the search for dark matter phenomenally difficult is the fact that not only can we not see it, but we don't have a clear idea of what we are looking for.
Now, researchers have begun to use a combination of models and state-of-the-art observations to put limits on the properties that dark matter might have. In a recent development, a team of scientists from Japan led by Associate Professor Wen Yin from Tokyo Metropolitan University have used a new spectrographic technique to observe light arriving from two galaxies, Leo V and Tucana II. They used the 6.5-m-wide Magellan Clay Telescope in Chile to collect light arriving on earth, paying close attention to the infrared region of the spectrum.
The team focused on a promising dark matter candidate, the axionlike particle (ALP), and considered how it "decays" and spontaneously emit light. Leading theoretical models make the near infrared part of the spectrum a particularly promising place to look. However, the infrared is also a crowded and confusing part of the electromagnetic spectrum. This is because of the vast range of sources of noise and interference from other sources. Examples include zodiacal light, the dim scatter of sunlight by interstellar dust, and light emitted by the atmosphere when it is heated by the sun. To get around this, in their previous work, they proposed a new technique which uses the fact that background radiation tends to include a broader range of wavelengths, whereas light from a specific decay process is more strongly skewed to a narrow range. Just like light spilling off a prism gets dimmer as different colors are spread thinner and thinner, decay events confined to a narrow range get sharper and sharper. Various state‐of‐the‐art infrared spectrographs—such as NIRSpec on the James Webb Space Telescope, WINERED on the Magellan Clay Telescope, and many others—can be used to implement this technique, effectively turning these instruments into excellent dark matter detectors.
Thanks to the precision of the team's technology (WINERED), they were able to account for all the light they detected in the near infrared to significant statistical accuracy. The fact that no decay was found was then used to set upper bounds on the frequency of these decay events, or a lower bound on the lifetime of ALP particles. Their new lower bound in seconds is 10 with 25 to 26 zeros after it, or ten to a hundred million times the age of the universe.
The finding is not only significant because this is the most stringent limit yet for the lifetime of dark matter. The work uses cutting-edge technology from infrared cosmology to address problems in fundamental particle physics. And while their conclusions are based on stringent analysis of the data so far, there are hints of anomalies or "excesses" which offer the tantalizing prospect of actual detection of dark matter with more data and more analysis. The search goes on for the missing piece of our universe.
This work was supported by JSPS KAKENHI Grant Numbers 22K14029, 20H05851, 21K20364, and 22H01215, and the Incentive Research Fund for Young Researchers from Tokyo Metropolitan University. WINERED data was gathered with the 6.5-m Magellan Clay Telescope located at Las Campanas Observatory, Chile, under the proposal "eV-Dark Matter search with WINERED." WINERED was developed by the University of Tokyo and the Laboratory of Infrared High-resolution Spectroscopy, Kyoto Sangyo University, under the financial support of JSPS KAKENHI Grant Numbers 16684001, 20340042, and 21840052, and 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 partly supported by JSPS KAKENHI Grant Number 19KK0080, JSPS Bilateral Program Number JPJSBP120239909, and Project Research Number AB0518 from the Astrobiology Center, NINS, Japan.
