Scientists Set Tightest Limits on Dark Matter’s Lifetime

Looking for dark matter is like looking for a black cat in a dark room, especially if there is no cat there. But dark matter seems to exist in the Universe, whatever it is. And now scientists have set the strictest limits on its existence. After all, in science, even without discovering something, you can make far-reaching conclusions. For example, what is the decay rate of dark matter or how long it can live in the Universe.

Dark matter has its own spectrum, which gives a chance to detect it. Image source: Tokyo Metropolitan University

The discovery was made by a team of scientists from Tokyo Metropolitan University. For the first time, they combined dark matter models and observations using state-of-the-art spectrometers. The scientists focused on finding a light version of dark matter, so-called ALP particles, or axion-like particles. These are some of the promising candidates for dark matter, the models of which are well developed.

One of the expected properties of ALP particles is spontaneous decay with the emission of light (photons). Scientists assumed that the spectrum of light from the decay of ALP particles would be somewhat different from the usual spectrum, for example, from the scattered zodiacal light or from the glow of the Earth’s atmosphere heated by the Sun. This is the near infrared range, in which ALP particles should emit characteristic spectra after decay. The problem is that near infrared light is overloaded with interference.

Scientists from Japan have developed an observation technique that, when combined with the latest near-infrared spectrographs, could help find the narrow spectra that accompany the decay of ALP particles. The researchers used the WINERED spectrograph on the 6.5-m Magellan telescope in Chile. In the future, they hope to gain access to the spectrographs of the James Webb Space Telescope. They collected light from two dwarf satellite galaxies of the Milky Way: Leo V and Tucana II. The analysis did not reveal any signs of decay of dark matter particles (ALP particles), but it did allow them to set limits on the lower threshold of its lifetime or the upper decay frequency.

The new and most stringent lower bound for the lifetime of ALP particles in seconds is 10 with 25–26 zeros after the decimal point, or 10 to 100 million times the age of the Universe. And although each individual dark matter particle may live seemingly forever compared to the Universe, according to the laws of quantum physics they still decay, and this is a chance to detect their presence and close the question of the century in astrophysics.