Collapsed Dark Matter Structures

TL;DR

This paper proposes a model where dark matter, charged under a 'dark electromagnetism', can form small, gravitationally collapsed structures, challenging the traditional view that dark matter cannot cool and collapse.

Contribution

It introduces a simple dark electromagnetism model allowing dark matter to form small-scale collapsed objects, expanding the possibilities for dark matter structure formation.

Findings

Dark matter can form small gravitationally collapsed objects.

Galaxies may host numerous dark matter substructures.

Potential observational signatures of these structures are unexplored.

Abstract

The distributions of dark matter and baryons in the Universe are known to be very different: the dark matter resides in extended halos, while a significant fraction of the baryons have radiated away much of their initial energy and fallen deep into the potential wells. This difference in morphology leads to the widely held conclusion that dark matter cannot cool and collapse on any scale. We revisit this assumption, and show that a simple model where dark matter is charged under a "dark electromagnetism" can allow dark matter to form gravitationally collapsed objects with characteristic mass scales much smaller than that of a Milky Way-type galaxy. Though the majority of the dark matter in spiral galaxies would remain in the halo, such a model opens the possibility that galaxies and their associated dark matter play host to a significant number of collapsed substructures. The observational signatures of such structures are not well explored, but potentially interesting.