The effect of stellar encounters on the dark matter annihilation signal from prompt cusps

Abstract

Prompt cusps are the densest quasi-equilibrium dark matter objects; one forms at the instant of collapse within every isolated peak of the initial cosmological density field. They have power-law density profiles, $\rho \propto r^{-1.5}$ with central phase-space density set by the primordial velocity dispersion of the dark matter. At late times they account for $\sim 1\%$ of the dark matter mass but for $>90\%$ of its annihilation luminosity in all but the densest regions, where they are tidally disrupted. Here we demonstrate that individual stellar encounters, rather than the mean galactic tide, are the dominant disruptors of prompt cusps within galaxies. Their cumulative effect is fully (though stochastically) characterised by an impulsive shock strength $B_{\ast }=2\pi G\int {\rho }_{\ast }(\mathbf{x}(t))\mathrm{d}t$ where ${\rho }_{\ast }$, the total mass density in stars, is integrated over a cusp's entire post-formation trajectory. Stellar encounters and mean tides have only a small effect on the halo annihilation luminosity seen by distant observers, but this is not true for the Galactic halo because of the Sun's position. For a 100 GeV WIMP, Earth-mass prompt cusps are predicted, and stellar encounters suppress their mean annihilation luminosity by a factor of two already at 20 kpc, so that their annihilation emission is predicted to appear almost uniform over the sky. The Galactic Center $\gamma$-ray Excess is thus unaffected by cusps. If it is indeed dark matter annihilation radiation, then prompt cusps in the outer Galactic halo and beyond must account for 20-80% of the observed isotropic $\gamma$-ray background in the 1 to 10 GeV range.

arXiv comment22 pages, 23 figures, for a video and code see https://github.com/jstuecker/cusp-encounters

References in corpus (49)

• The Structure of Cold Dark Matter Halos
• The Cosmic Linear Anisotropy Solving System (CLASS) II: Approximation schemes
• Ellipsoidal collapse and an improved model for the number and spatial distribution of dark matter haloes
• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• The mass distribution and gravitational potential of the Milky Way
• Small Scale Cosmological Perturbations: An Analytic Approach
• The Waning of the WIMP? A Review of Models, Searches, and Constraints
• The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV
• Dark Matter Annihilation in The Galactic Center As Seen by the Fermi Gamma Ray Space Telescope
• WIMP dark matter candidates and searches - current status and future prospects
• Earth-mass dark-matter haloes as the first structures in the early Universe
• The Milky Way total mass profile as inferred from Gaia DR2
• Disruption of Dark Matter Substructure: Fact or Fiction?
• Cores in warm dark matter haloes: a Catch 22 problem
• Effects of cold dark matter decoupling and pair annihilation on cosmological perturbations
• The Compression of Dark Matter Halos by Baryonic Infall
• Galactic Bulge Preferred Over Dark Matter for the Galactic Center Gamma-Ray Excess
• Phat ELVIS: The inevitable effect of the Milky Way's disk on its dark matter subhaloes
• Hierarchical Formation of Dark Matter Halos and the Free Streaming Scale
• The Fermi-LAT GeV Excess Traces Stellar Mass in the Galactic Bulge
• The characteristics of the Galactic center excess measured with 11 years of Fermi-LAT data
• The survival and disruption of CDM micro-haloes: implications for direct and indirect detection experiments
• Density Profiles of CDM Microhalos and their Implications for Annihilation Boost Factors
• Can tides disrupt cold dark matter subhaloes?
• Gamma-ray Signal from Earth-mass Dark Matter Microhalos
• The asymptotic tidal remnants of cold dark matter subhalos
• Constraints on Decaying Dark Matter from the Isotropic Gamma-Ray Background
• Strong Evidence that the Galactic Bulge is Shining in Gamma Rays
• Earth-mass haloes and the emergence of NFW density profiles
• Density profiles of ultracompact minihalos: Implications for constraining the primordial power spectrum
• Strong constraints on thermal relic dark matter from Fermi-LAT observations of the Galactic Center
• Are ultracompact minihalos really ultracompact?
• Impact of Dark Matter Microhalos on Signatures for Direct and Indirect Detection
• On mini-halo encounters with stars
• Inner cusps of the first dark matter haloes: Formation and survival in a cosmological context
• Stellar Disruption of Axion Miniclusters in the Milky Way
• Predicting the density profiles of the first halos
• What sets the central structure of dark matter haloes?
• Fingerprints of the initial conditions on the density profiles of cold and warm dark matter haloes
• Dark matter halo cores and the tidal survival of Milky Way satellites
• Analysis of galactic tides and stars on CDM microhalos
• Phase-space structure of protohalos: Vlasov versus Particle-Mesh
• Tidal Stripping in the Adiabatic Limit
• Tidal evolution of dark matter annihilation rates in subhalos
• Evolution of dark matter microhalos through stellar encounters
• Prompt cusp formation from the gravitational collapse of peaks in the initial cosmological density field
• Shedding light on low-mass subhalo survival and annihilation luminosity with numerical simulations
• Dark matter annihilation and the Galactic Centre Excess
• Tidal stripping of dark matter subhalos by baryons from analytical perspectives: disk shocking and encounters with stars

Cited by in corpus (10)

• Prompt cusps and the dark matter annihilation signal
• Limits on dark matter annihilation in prompt cusps from the isotropic gamma-ray background
• The Disruption of Dark Matter Minihalos by Successive Stellar Encounters
• Can prompt cusps of WIMP dark matter be detected as individual gamma-ray sources?
• 21-cm Constraints on Dark Matter Annihilation after an Early Matter-Dominated Era
• Collisionless relaxation from near equilibrium configurations: Linear theory and application to tidal stripping
• The cusp-halo relation
• Limits on Early Matter Domination from the Isotropic Gamma-Ray Background
• Excursion Sets with a "Perfect" Collapse Model
• Prompt cusps in hierarchical dark matter halos: Implications for annihilation boost