The rotational behaviour of spiral galaxies can not be explained by the visible matter in the galaxy. So it was posited that there was an invisible halo of dark matter around them that would explain the anomalous behaviour. This explanation appears supported by gravitational lensing. However...
No trace of dark matter halos (https://phys.org/news/2022-08-dark-halos.html)
"According to the standard model of cosmology, the vast majority of galaxies are surrounded by a halo of dark matter particles. This halo is invisible, but its mass exerts a strong gravitational pull on galaxies in the vicinity. A new study led by the University of Bonn (Germany) and the University of Saint Andrews (Scotland) challenges this view of the Universe. The results suggest that the dwarf galaxies of Earth's second closest galaxy cluster—known as the Fornax Cluster—are free of such dark matter halos. The study appeared in the journal Monthly Notices of the Royal Astronomical Society."
Curiouser and cuiouser!