Although dark matter is a central part of the standard cosmological model, it’s not without its issues. There continue to be nagging mysteries about the stuff, not the least of which is the fact that scientists have found no direct particle evidence of it.

Despite numerous searches, we have yet to detect dark matter particles. So some astronomers favor an alternative, such as modified Newtonian dynamics (MoND) or modified gravity model. And a new study of galactic rotation seems to support them.

The idea of MoND was inspired by galactic rotation. Most of the visible matter in a galaxy is clustered in the middle, so you’d expect that stars closer to the center would have faster orbital speeds than stars farther away, similar to the planets of our solar system. What we observe is that stars in a galaxy all rotate at about the same speed. The rotation curve is essentially flat rather than dropping off. The dark matter solution is that galaxies are surrounded by a halo of invisible matter, but in 1983 Mordehai Milgrom argued that our gravitational model must be wrong.

Scientists from the Large High Altitude Air Shower Observatory (LHAASO) have presented roughly 1.5 years of observational data, calculating new limits on the lifetime of heavy dark matter particles that have masses between 10⁵ and 10⁹ giga-electron volts.

The study, titled “Constraints on heavy decaying dark matter from 570 days of LHAASO observations,” was recently published in Physics Review Letters.

The gravitational model of the Milky Way shows that there is a very high density of dark matter in the galactic center, and the gamma rays produced by the decay of this dark matter will radiate from the galactic center to the surroundings for hundreds of light-years or even thousands of light-years. However, for a long time, the observation of ultra-high-energy gamma rays produced by heavy dark matter has been complicated by the presence of other background radiation.

What were the first moments of the Universe like? It’s a mystery that scientists have been trying to unravel for decades. The ALICE collaboration at CERN is a specialist in the subject: this detector (A Large Ion Collider Experiment) was designed to study quark-gluon plasma, a phase of matter that would have existed just after the Big Bang. And the team recently succeeded in recreating and characterizing this very first hypothetical material, using the Large Hadron Collider (LHC).