Dark matter particle theories have a long string of documented problems. Here is another one.
Cold dark matter (CDM) has faced a number of challenges mainly at small scales, such as the too-big-to-fail problem, and core-cusp density profile of dwarf galaxies. Such problems were argued to have a solution either in the baryonic physics sector or in modifying the nature of dark matter to be self-interacting, or self-annihilating, or ultra-light. Here we present a new challenge for CDM by showing that some of Milky Way's satellites are too dense, requiring the formation masses and redshifts of halos in CDM not compatible with being a satellite. These too-dense-to-be-satellite systems are dominated by dark matter and exhibit a surface density above mean dark matter cosmic surface density. This value corresponds to dark matter pressure of . This problem, unlike other issues facing CDM, has no solution in the baryonic sector and none of the current alternatives of dark matter can account for it. The too-dense-to-be-satellite problem presented in this work provides a new clue for the nature of dark matter, never accounted for before.
Mohammadtaher Safarzadeh, Abraham Loeb "A New Challenge for Dark Matter Models" arXiv:2017.03478 (July 7, 2021).