At https://phys.org/news/2019-08-heavyweight-candidate-dark.html … according to current theory a quarter of the universe is composed of dark matter – sitting in the shadows. Its presence is determined by gravitational pull. What dark matter is made of is a complete mystery. Scientists at the Max Planck Institute for Gravitational Physics have come up with a new theory – the existence of a hypothetical particle, gravitinos. Its existence follows on from a theory that seeks to explain the spectrum of quarks and leptons in the standard model of particle physics.
The standard model concerns the building blocks of matter and the forces that hold them together. It claims there ar six different quarks and six leptons grouped into 3 families. However, the matter around us is made up of only 3 particles from the first of the families – two quarks (up and donw) and the electron (a lepton). The long established standard model (an hypothesis that became mainstream fundamental thinking) has rmained unchanged for a long time. The large hadron collider at CERN had as its main purpose, explaining beyond the standard model. After ten years of data scientists have failed to detect any other elementary particle (apart from Higgs Bosun). Mainstream scientists, observing the cosmos, say it cannot be explained by ordinary matter. One sign of this is that galaxies rotate at high speeds and visible matter of the universe is not enought to hold them together. So far, nobody nobody knows what the missing matter is – yet alone its properties. The existence of dark matter, although entirely theoretical, weighs heavily on the minds of cosmologists. The gravatino, a heavy element rather than the lightweight WIMPs of earlier speculation, it is hoped, will provide the answer. The problem is that gravatinos aren't easy to spot – even if they exist. Interestingly, they are projected to have strong electromagnetic interactions with ordinary matter. The idea now is to search for relics of gravatinos deep underground in case they have been preserved over millions, if not billions, of years, within the crust. Digging a hole you might say.