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Constraints on primordial black holes as dark matter candidates from capture by neutron stars

Fabio Capela, Maxim Pshirkov, Peter Tinyakov

TL;DR

The paper addresses whether primordial black holes can constitute all dark matter by examining their capture by neutron stars. It quantifies the energy loss and capture rates of PBHs traversing NSs, with a focus on environments like globular cluster cores that host high DM densities and low velocity dispersions. The analysis shows that, under plausible GC-core DM densities around $2\times 10^{3}$ GeV/cm$^3$, PBHs with masses up to roughly $5\times 10^{24}$ g cannot make up all of DM, with tighter bounds for higher densities and lower velocities. These results extend previous PBH-DM constraints to higher masses and stress that any PBH-DM scenario must feature a very narrow mass distribution, while also highlighting that Galactic-center constraints are less competitive unless DM densities and kinematics are extreme. Overall, the work tightens the allowed PBH parameter space by linking NS survivability to halo DM properties in DM-rich astrophysical environments.

Abstract

We investigate constraints on primordial black holes (PBHs) as dark matter candidates that arise from their capture by neutron stars (NSs). If a PBH is captured by a NS, the star is accreted onto the PBH and gets destroyed in a very short time. Thus, mere observations of NSs put limits on the abundance of PBHs. High DM densities and low velocities are required to constrain the fraction of PBHs in DM. Such conditions may be realized in the cores of globular clusters if the latter are of a primordial origin. Assuming that cores of globular clusters possess the DM densities exceeding several hundred GeV/cm$^3$ would imply that PBHs are excluded as comprising all of the dark matter in the mass range $3\times 10^{18} \text{g} \lesssim m_\text{BH}\lesssim 10^{24} \text{g}$. At the DM density of $2\times 10^3$ GeV/cm$^3$ that has been found in simulations in the corresponding models, less than 5% of the DM may consist of PBH for these PBH masses.

Constraints on primordial black holes as dark matter candidates from capture by neutron stars

TL;DR

The paper addresses whether primordial black holes can constitute all dark matter by examining their capture by neutron stars. It quantifies the energy loss and capture rates of PBHs traversing NSs, with a focus on environments like globular cluster cores that host high DM densities and low velocity dispersions. The analysis shows that, under plausible GC-core DM densities around GeV/cm, PBHs with masses up to roughly g cannot make up all of DM, with tighter bounds for higher densities and lower velocities. These results extend previous PBH-DM constraints to higher masses and stress that any PBH-DM scenario must feature a very narrow mass distribution, while also highlighting that Galactic-center constraints are less competitive unless DM densities and kinematics are extreme. Overall, the work tightens the allowed PBH parameter space by linking NS survivability to halo DM properties in DM-rich astrophysical environments.

Abstract

We investigate constraints on primordial black holes (PBHs) as dark matter candidates that arise from their capture by neutron stars (NSs). If a PBH is captured by a NS, the star is accreted onto the PBH and gets destroyed in a very short time. Thus, mere observations of NSs put limits on the abundance of PBHs. High DM densities and low velocities are required to constrain the fraction of PBHs in DM. Such conditions may be realized in the cores of globular clusters if the latter are of a primordial origin. Assuming that cores of globular clusters possess the DM densities exceeding several hundred GeV/cm would imply that PBHs are excluded as comprising all of the dark matter in the mass range . At the DM density of GeV/cm that has been found in simulations in the corresponding models, less than 5% of the DM may consist of PBH for these PBH masses.

Paper Structure

This paper contains 7 sections, 24 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Capture of black holes by compact stars
  3. Energy Loss
  4. Capture Rate
  5. Constraints
  6. Conclusions
  7. Calculation of the friction force

Figures (2)

  • Figure 1: Constraints on the fraction of PBHs in the total amount of DM from various observations as explained in Sect. \ref{['sec:introduction']} (red shaded regions). The green shaded region shows constraints derived in this paper, which would follow from observations of NSs in the cores of globular clusters if one assumes the DM density of $2\times 10^3$ GeV/cm$^3$ as obtained in numerical simulations.
  • Figure 2: The dependence of the constraints on the fraction $\Omega_\text{PBH}/\Omega_\text{DM}$ of PBHs in the total amount of DM on the assumed DM density in the core of a GC. Three cases are shown: $\rho_\text{DM}=4\times 10^{2}~\text{GeV}\text{cm}^{-3}$, $\rho_\text{DM}=2\times 10^{3}~\text{GeV}\text{cm}^{-3}$ (the same as in Fig. \ref{['fig:constraints']}), and $\rho_\text{DM}=10^{4}~\text{GeV}\text{cm}^{-3}$.