On the survival and disruption of Earth mass CDM micro-haloes

TL;DR

This paper argues that Earth-mass CDM micro-haloes are more resilient to Galactic tidal disruption than previously thought, likely surviving over cosmic timescales and potentially detectable via gamma-ray emissions.

Contribution

It corrects prior assumptions about stellar disruption of micro-haloes by applying the impulse approximation to multiple encounters, showing their survival over a Hubble time.

Findings

Micro-haloes can survive several Hubble times despite stellar interactions.

Tidal heating by stars does not significantly reduce micro-halo abundance.

Central cores of micro-haloes may be detectable as gamma-ray sources.

Abstract

Neutralino dark matter leads to the formation of numerous earth mass dark matter haloes at redshifts z\approx 60 (Diemand et al. 2005). These abundant CDM micro-haloes have cuspy density profiles that can easily withstand the Galactic tidal field at the solar radius. Zhao, Taylor, Silk & Hooper (astro-ph/0502049) concluded that ``...the majority of dark matter substructures with masses \sim 10^{-6}M_o will be tidally disrupted due to interactions with stars in the Galactic halo''. However these authors assumed a halo density of stars that is at least an order of magnitude higher than observed. We show that the appropriate application of the impulse approximation is to the regime of multiple encounters, not single disruptive events as adopted by Zhao et al., which leads to a survival time of several Hubble times. Therefore we do not expect the tidal heating by Galactic stars to affect the abundance of micro-haloes. Disk crossing will cause some mass loss but the central cores are likely to survive and could be detected as gamma-ray sources with proper motions of several arc minutes per year.