Cold dark matter microhalo survival in the Milky Way

Abstract

A special purpose N-body simulation has been built to understand the tidal heating of the smallest dark matter substructures (10 −6 M and 0.01 pc) from the grainy potential of the Milky Way due to individual stars in the disc and the bulge. To test the method, we first run simulations of single encounters of microhaloes with an isolated star, and compare with analytical predictions of the dark particle bound fraction as a function of impact parameter. We then follow the orbits of a set of microhaloes in a realistic flattened Milky Way potential. We concentrate on (detectable) microhaloes passing near the Sun with a range of pericentre and apocentre. Stellar perturbers near the orbital path of a microhalo would exert stochastic impulses, which we apply in a Monte Carlo fashion according to the Besançon model for the distribution of stars of different masses and ages in our Galaxy. Also incorporated are the usual pericentre tidal heating and disc shocking. We give a detailed diagnosis of typical microhaloes and find microhaloes with internal tangential anisotropy are slightly more robust than the ones with radial anisotropy. In addition, the dark particles generally go through of a random walk in velocity space and diffuse out of the microhaloes. We show that the typical destruction timescales are strongly correlated with the stellar density averaged along a microhalo's orbit over the age of the stellar disc. We also present the morphology of a microhalo at several epochs which may hold the key to dark matter detections. We checked our results against different choices of microhalo mass, virial radius and anisotropy.

Gravitational Lensing Signatures of Axion Dark Matter Minihalos in Highly Magnified Stars

“…If the number density of perturbers only decreases approximately as m −1 2 , dynamical heating should be dominated by the most massive perturbers. Tidal interactions between generic small halos and passing stars have been extensively studied (Goerdt et al 2007;Green & Goodwin 2007;Angus & Zhao 2007;Zhao et al 2007). Here we present a simple order-of-magnitude estimate applied to axion minihalos.…”

The dark matter annihilation boost from low-temperature reheating

“…The earth-mass microhalos that form in cosmological scenarios without an EMDE are more vulnerable to stripping by stellar encounters than by the host halo [77,78,[87][88][89][90][91][92]. Although these microhalos are expected to lose a considerable fraction of their mass due to interactions with stars, some high-density cores should survive [78,88,92].…”

The collision velocity of the bullet cluster in conventional and modified dynamics

“…For this procedure, the only two unknowns are the separation, which is initially known and computed in each time‐step, and the mass enclosed. The enclosed mass depends on the density profile of the two clusters and was fitted by Clowe et al (2006) using Navarro–Frenk–White (NFW) profiles of the form (see Angus & McGaugh 2007): where c is the concentration. The enclosed mass goes as …”