Scientists may have finally found the way to directly detect dark matter

For nearly a century, scientists have grappled with the enigma of dark matter, an unseen substance believed to shape galaxies and the universe itself. While its gravitational influence is evident in galactic rotation curves, its fundamental properties—mass and non-gravitational interactions—remain elusive.

Despite decades of research, no direct detection has been made. Now, a groundbreaking approach using advanced infrared spectrographs may offer a new way forward in the search for this cosmic mystery.

One promising dark matter candidate is the axion-like particle (ALP), a theoretical elementary particle that interacts with photons. Some models predict ALPs in the mass range of 0.01 to 7.7 electron volts (eV). These particles could decay into two photons, creating narrow-line emissions in the infrared spectrum.

Unlike the hot dark matter theory of the 1980s, which suggested particles too light to form structures like galaxies, ALPs could act as cold dark matter under certain production conditions.

Recent research suggests that ALPs could explain anomalies in the cosmic infrared background if their mass is near 2 eV. Theoretical studies also indicate that if their photon coupling strength reaches around GeV, they could simultaneously account for two independent cosmic infrared excesses. Motivated by these possibilities, researchers have turned to state-of-the-art spectrographs to hunt for ALPs.

A team from Tokyo Metropolitan University, led by Associate Professor Wen Yin, has harnessed cutting-edge infrared spectrographs to search for signs of dark matter decay. They used the Warm Infrared Echelle Spectrograph for Realizing Extreme Dispersion and Sensitivity (WINERED), installed on the 6.5-meter Magellan Clay Telescope in Chile.

This high-resolution instrument, developed by the University of Tokyo and Kyoto Sangyo University, offers unparalleled sensitivity in the near-infrared spectrum (0.9–1.35 micrometers). With a spectral resolution reaching up to R=68,000, WINERED allows for precise detection of narrow spectral lines that could indicate the presence of ALP decay.

The team observed the Leo V dwarf spheroidal galaxy for one hour on July 6, 2023, followed by 30 minutes of blank sky observation to eliminate background noise. On November 2, 2023, they conducted a second session, targeting the Tucana II galaxy for 1.2 hours, with 0.7 hours of blank sky observation. By analyzing the data, they searched for excess infrared emissions that could signal ALP decay.

Despite the precision of their measurements, no clear decay signatures were found. However, this absence of detection provided valuable constraints on ALP properties. The researchers established one of the strongest limits yet on dark matter decay rates for masses between 1.8 and 2.7 eV. Their findings suggest that if ALPs exist, they have an incredibly long lifetime—at least to seconds, roughly ten to a hundred million times the age of the universe.

Their study also demonstrated the effectiveness of infrared spectrographs in dark matter searches. Unlike other methods that rely on indirect background models, their approach directly measured spectral lines, ensuring robust results.

Their work complements other dark matter searches, such as those using the Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST). The JWST method, which subtracts continuous background spectra, provides an alternative way to constrain dark matter properties, though its effectiveness is limited in certain regions of the sky due to interstellar absorption.

The results mark a significant advancement in dark matter research. By leveraging cutting-edge technology, scientists are pushing the boundaries of what is known about the cosmos.

Even though no direct detection was made, the findings provide a crucial benchmark for future studies. The team also noted anomalies in their data—potential hints of unexplained excess emissions—that warrant further investigation.

With additional observations and improved techniques, the search for dark matter continues. By refining these methods and expanding the search to different wavelengths, researchers hope to uncover the missing piece of the cosmic puzzle.

The quest to understand dark matter is far from over, but with each study, scientists get closer to revealing the true nature of this mysterious substance.

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