Dark matter spikes around Sgr A* in γ-rays

The abnormally fast orbital decay observed in the black hole (BH) Low-Mass X-ray binaries (BH-LMXB) A0620-00 and XTE J1118+480 can be explained by the dynamical friction between Dark Matter (DM) and the companion star orbiting around the low-mass BH (≃ a few M ⊙) of the system. In this case the value of the index γ sp of the DM spike surrounding the BH can be pinned down with an accuracy of ≃ a few percent, way better than that for much bigger systems such as the super massive BHs (SMBHs) in the Galactic Center or in M87. We have used data from XTE J1118+480 to put bounds on the WIMP annihilation cross section times velocity ⟨σv⟩, assuming that DM annihilation is driven by the χχ → bb̅ annihilation channel and that it proceeds in s-wave. The bounds are driven by the radio synchrotron signal produced by e ± final states propagating in the magnetic field in the vicinity of the BH. We find that for DM masses m χ up to the TeV scale XTE J1118+480 allows to constrain ⟨σv⟩ well below the standard value ⟨σv⟩thermal, corresponding to the observed DM relic density in the Universe for a thermal WIMP. On the other hand, for m χ ≳ 15 GeV, the bounds from the SMBHs in the GC or in M87 do not reach ⟨σv⟩thermal when the very large uncertainties on the corresponding spike indices are taken into account, in spite of potentially producing much larger DM densities compared to XTE J1118+480. Our bounds for XTE J1118+480 have a mild sensitivity on the effect of spatial diffusion (which implies at most a weakening of the bounds of a factor ≲ 6 at large m χ). However, diffusion is instrumental in enhancing the sensitivity of the results upon the intensity of the magnetic field. In particular, our bounds rest on the assumption that the magnetic field B reaches the equipartition value B eq. We find that a reduction factor of the magnetic field B eq/B larger than about 14 at low m χ, becoming progressively smaller at higher WIMP masses, would be sufficient to relax the XTE J1118+480 bound to the level of other existing bounds. Recent estimates, albeit not conclusive, may suggest values of B eq/B in BH-LMXB systems as large as 20. This implies that the intensity of the magnetic field in BH-LMXB systems represents the major uncertainty in using them as an alternative to heavier BHs to search for WIMPs.

Section: Resultsmentioning

confidence: 99%

WIMP constraints from black hole low-mass X-ray binaries

Kar,

Kim,

Kim

et al. 2024

“…The possible BH spike on top of the galactic density is estimated as (see e.g. [24,35,[42][43][44][45])…”

Section: Dark Matter Influence On Gravitational Wavesmentioning

confidence: 99%

“…with power p ≈ 1.5-2.5. According to computations that assume adiabatic growth and that are not tested by simulations, a larger p ′ is expected to increase the spike power index as p ≈ (9 − 2p ′ )/(4 − p ′ ) [42,45]. General-relativistic corrections to the adiabatic growth of the DM density distribution are not expected to be relevant at the radii relevant for us, much bigger than the Schwarzschild radius [46].…”

Section: Jcap02(2024)054mentioning

confidence: 99%

See 1 more Smart Citation

Probing the Dark Matter density with gravitational waves from super-massive binary black holes

Ghoshal,

Strumia

2024

Supermassive black hole binaries source gravitational waves measured by Pulsar Timing Arrays. The frequency spectrum of this stochastic background is predicted more precisely than its amplitude. We argue that Dark Matter friction can suppress the spectrum around nHz frequencies, where it is measured, allowing to derive robust and significant bounds on the Dark Matter density, which, in turn, controls indirect detection signals from galactic centers. A precise spectrum of gravitational waves would translate in a tomography of the DM density profile, potentially probing DM particle-physics effects that induce a characteristic DM density profile, such as DM annihilations or de Broglie wavelength.

“…Despite the benchmark approach in DM indirect searches, which aims to set constraints on the DM annihilation cross-section by selecting a couple of possible (typically, one core and one cusp) DM density distribution profiles (see e.g. [49,50]), our main focus is to set constraints on the DM density profile within in a radius of 450 pc from the GC, by assuming a thermal DM candidate which could explain the gamma-ray spectra detected by H.E.S.S. in the inner 15 pc of the Galaxy [17,18].…”

Section: Introductionmentioning

confidence: 99%

Multi-TeV dark matter density in the inner Milky Way halo: spectral and dynamical constraints

Zuriaga-Puig,

Gammaldi,

Gaggero

et al. 2023

We develop a comprehensive study of the gamma-ray flux observed by the High Energy Stereoscopic System (H.E.S.S.) in 5 regions of the Galactic Center (GC). Motivated by previous works on a possible Dark Matter (DM) explanation for the TeV cut-off observed by H.E.S.S. in the innermost ∼ 15 pc of the Galaxy, we aim to constrain the DM distribution up to a radius of ∼ 450 pc from the GC. In this region, the benchmark approach (e.g. cosmological simulations and Galactic dynamics studies) fails to produce a strong prediction of the DM profile. Within our proof-of-concept analysis, we use DRAGON to model the diffuse background emission and determine upper limits on the density distribution of thermal multi-TeV Weakly Interactive Massive Particles (WIMPs), compatible with the observed gamma-ray flux. The results are in agreement with the hypothesis of an enhancement of the DM density in the GC with respect to the benchmark Navarro-Frenk-White (NFW) profile (γ = 1) and allow us to exclude profiles with an inner slope cuspier than γ ≳ 1.3. We also investigate the possibility that such an enhancement could be related to the existence of a DM spike associated with the supermassive black hole Sgr A* at the GC. We find out that the existence of an adiabatic DM spike smoothed by the scattering off of WIMPs by the bulge stars may be consistent with the observed gamma-ray flux if the spike forms on an underlying generalized NFW profile with γ ≲ 0.8, corresponding to a spike slope of γsp-star = 1.5 and spike radius of R sp-stars ∼ 25 30 pc. Instead, in the extreme case of the instantaneous growth of the black hole, the underlying profile could have up to γ ∼ 1.2, a corresponding γsp-inst = 1.4 and R sp-inst ∼ 15–25 pc. Finally, the results of our analysis of the total DM mass enclosed within the S2 orbit (updated with new GRAVITY data) are less stringent than the spectral analysis. Our work aims to guide future studies of the GC region, with both current and next generation of telescopes. In particular, the next Cherenkov Telescope Array will be able to scan the GC region with improved flux sensitivity and angular resolution.