Abstract
We use a semianalytic approach that is calibrated to N-body simulations to study the evolution of self-interacting dark matter cores in galaxies. We demarcate the regime where the temporal evolution of the core density follows a well-defined track set by the initial halo parameters and the cross section. Along this track, the central density reaches a minimum value set by the initial halo density. Further evolution leads to an outward heat transfer, inducing gravothermal core collapse such that the core shrinks as its density increases. We show that the time scale for the core collapse is highly sensitive to the outer radial density profile. Satellite galaxies with significant mass loss due to tidal stripping should have larger central densities and significantly faster core collapse compared to isolated halos. Such a scenario could explain the dense and compact cores of dwarf galaxies in the Local Group like Tucana (isolated from the Milky Way), the classical Milky Way satellite Draco, and some of the ultrafaint satellites. If the ultimate fate of core collapse is black hole formation, then the accelerated time scale provides a new mechanism for creating intermediate mass black holes.
Highlights
Self-interacting dark matter (SIDM) [1,2,3] is a compelling framework for explaining the small-scale structure formation puzzles [4]
We investigate the evolution of a dark matter halo in the presence of self interactions using a semianalytic method, originally developed to study gravothermal collapse in globular clusters [19, 20] and later applied to isolated SIDM halos [21, 22]
We showed that for σm < 10 cm2/g, the halo core density follows a track defined by the outer halo parameters, attaining a minimum value of ∼ 3 ρs
Summary
Self-interacting dark matter (SIDM) [1,2,3] is a compelling framework for explaining the small-scale structure formation puzzles [4]. We investigate the evolution of a dark matter halo in the presence of self interactions using a semianalytic method, originally developed to study gravothermal collapse in globular clusters [19, 20] and later applied to isolated SIDM halos [21, 22] This method allow us to track the full halo evolution at scales ≤ 100 pc, which are expensive to achieve with N-body simulations. We first characterize the full process of SIDM halo evolution, whereby large cores can be created today for cross sections of ∼ 1 cm2/g and the gravothermal collapse phase sets in for larger cross sections, as seen in simulations We show that this temporal evolution is accelerated if the outer region of the halo is stripped, resulting in a higher density core today. We discuss the possible consequences of core collapse of the SIDM halo for intermediate-mass black hole formation
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