Astronomers continue to investigate and test new ideas about the sources of dark matter particles. One such approach, described in a new paper published in the journal Physical Review Letters, suggests that if dark matter consists of axions, then we might see signs of their decay near glowing pulsars.

While the most popular candidates for dark matter are weakly massive particles (WIMPs), another popular option is the hypothetical axis. Axions were initially proposed not to solve the dark matter problem, but to clear up some confusing intricacies of particle physics. According to the theory, axions are low-mass, uncharged particles that do not interact strongly with ordinary matter or light, making them ideal candidates for dark matter. Axions can decay into photons, but the resulting light will be so rarefied and faint that we cannot detect it.

This work suggested a way to detect the residual glow of axions: If they exist, they could be created in extremely strong magnetic fields, such as in neutron stars and black holes. Pulsars have the strongest electromagnetic fields, so that’s the best place to look. Pulsars are neutron stars that produce powerful flows of energy from their magnetic poles. Polar regions can also form multiple axions, some of which can be converted into photons. Therefore, theoretically, light from pulsars should contain traces of axis decay.

The researchers estimated the amount and spectrum of light that would be produced by the decay of the axes. They then simulated how this would show up in the radio bursts of powerful pulsars. And they compared their model with observations of 27 nearby pulsars to find excess light that would confirm the decay of the axions.

The team found no evidence of the existence of axes. However, based on their observations, they managed to limit the mass of the axes. According to the data, the mass of the axions cannot be less than 10-8 electronvolts and cannot be heavier than 10-5 electronvolts, which is much less than even neutrinos.

One advantage of this is that it does not suggest that the axions are dark matter particles, it just assumes their existence. The result turns out to be more important for particle physics than cosmology, so the mass constraint may be useful in future research. But dark matter particles remain hidden.