It has been suggested for a long time that dark matter would form a density spike around a black hole. However, no promising evidence has been observed so far to verify this theoretical suggestion. Here, we report the existence of a dark matter density spike around each of the two nearby stellar-mass black holes (A0620-00 and XTE J1118+480). The dynamical friction between dark matter and the companion stars can satisfactorily explain the abnormally fast orbital decays in the two binaries. The calculated spike index for A0620-00 and XTE J1118+480 is γ = 1.71 − 0.02 + 0.01 and γ = 1.85 − 0.04 + 0.04 , respectively, which are close to the lower regime predicted by the stellar heating model. It may provide possible indirect evidence for the existence of dark matter density spikes around stellar-mass black holes. We anticipate that analyzing observational data of nearby black hole X-ray binaries would be a new way to reveal the nature of dark matter.

Recent gamma-ray and cosmic-ray observations have put strong constraints on the amount of primordial black holes (PBHs) in our universe. In this paper, we use the archival radio data of the inner Galactic Centre to constrain the PBH to dark matter ratio for three different PBH mass distributions including monochromatic, lognormal, and power law. We show that the amount of PBHs only constitutes a very minor component of dark matter at the Galactic Centre for a large parameter space.

Over the past few years, some studies have claimed that annihilating dark matter with mass ∼10–100 GeV can explain the GeV gamma-ray excess in our Galaxy. However, recent analyses of Fermi-LAT and radio observational data have ruled out the possibility of the thermal relic annihilating dark matter with mass m ≤ 100 GeV for some popular annihilation channels. By using the new observed radio data of the Andromeda galaxy, we rule out the existence of ∼100–300 GeV thermal relic annihilating dark matter for 10 annihilation channels. The lower limits of annihilating dark matter mass are improved to larger than 330 GeV for the most conservative case, which is a few times larger than the current best constraints. Moreover, these limits strongly disfavor the benchmark model of weakly interacting massive particles produced through the thermal freeze-out mechanism.

Recently, the discovery of the radial acceleration relation (RAR) in galaxies has been regarded as an indirect support of alternative theories of gravity such as modified Newtonian dynamics (MOND) and modified gravity. This relation indicates a tight correlation between dynamical mass and baryonic mass in galaxies with different sizes and morphology. However, if the RAR relation is scale independent and could be explained by alternative theories of gravity, this relation should be universal and true for galaxy clusters as well. In this article, by using the X-ray data of a sample of galaxy clusters, we investigate if there exists any tight correlation between dynamical mass and baryonic mass in galaxy clusters, assuming hot gas mass distribution almost representing baryonic distribution and that the galaxy clusters are virialized. We show that the resulting RAR of 52 non-cool-core galaxy clusters scatters in a large parameter space, possibly due to our simplifying assumptions and unclear matter content in galaxy clusters. This might indicate that the RAR is unlikely to be universal and scale independent.

If dark matter is composed of massive bosons, a Bose–Einstein condensation process must have occurred during the cosmological evolution. Therefore galactic dark matter may be in a form of a...

Black hole dynamics suggests that dark matter would redistribute near a supermassive black hole (SMBH) to form a density spike. However, no direct evidence of a dark matter density spike around an SMBH has been identified. In this Letter, we present the first robust evidence showing a dark matter density spike around an SMBH. We revisit the data of the well-known SMBH binary OJ 287 and show that the inclusion of the dynamical friction due to a dark matter density spike around the SMBH can satisfactorily account for the observed orbital decay rate. The derived spike index γ sp = 2.351 − 0.045 + 0.032 gives an excellent agreement with the value γ _sp = 2.333 predicted by the benchmark model assuming an adiabatically growing SMBH. This provides a strong verification of the canonical theory suggested two decades ago modeling the gravitational interaction between collisionless dark matter and SMBHs.