Dark compact objects: An extensive overview

We study the structure of compact objects that contain non-self annihilating, self-interacting dark matter admixed with ordinary matter made of neutron star and white dwarf materials. We extend the previous work [Phys. Rev. D 92, 123002 (2015)] on these dark compact objects by analyzing the effect of weak and strongly interacting dark matter with particle masses in the range of 1–500 GeV, so as to set some constraints in the strength of the interaction and the mass of the dark matter particle. We find that the total mass of the compact objects increases with decreasing dark matter particle mass. In the strong interacting case and for dark matter particle masses in the range 1–10 GeV, the total mass of the compact objects largely exceeds the $2M_{\odot }$ constraint for neutron star masses and the nominal $1M_{\odot }$ for white dwarfs, while for larger dark matter particle masses or in the weakly interacting case the compact objects show masses in agreement or smaller than these constraints, thus hinting at the exclusion of strongly self-interacting dark matter of masses 1–10 GeV in the interior of these compact objects. Moreover, we observe that the smaller the dark matter particle mass, the larger the quantity of dark matter captured is, putting constraints on the dark matter mass trapped in the compact objects so as to fulfill $\simeq 2M_{\odot }$ observations. Finally, the inhomogeneity of distribution of dark matter in the Galaxy implies a mass dependence of compact objects from the environment which can be used to put constraints on the characteristics of the Galaxy halo DM profile and on particle mass. In view of these results, we discuss the formation of the dark compact objects in an homogeneous and nonhomogeneous dark matter environment.

Figure 1

Mass and radius of OM content of the astrophysical objects as a function of the central pressure of OM for the DM interaction strength parameters $y={10}^{-1}$ (left panels) and $y={10}^3$ (right panels). The solutions go through both stable and unstable regions. The separations are delimited by the roughly vertical dashed curves. The colored lines indicate solutions for $M_{\mathrm{OM}}$ and $R_{\mathrm{OM}}$ over OM central pressures for a set of dimensionless ratio, $p_{\mathrm{DM}}/p_{\mathrm{OM}}$, running from ${10}^{-5}$ to $10^5$. Those lines turn grey in the unstable regions. Note that for the case $y={10}^{-1}$, lines of $p_{\mathrm{DM}}/p_{\mathrm{OM}}={10}^{-1}$ to $p_{\mathrm{DM}}/p_{\mathrm{OM}}={10}^{-5}$ for the $M_{\mathrm{OM}}$ and $R_{\mathrm{OM}}$ distributions lie on top of each other.

Figure 2

Mass and radius of DM content of the astrophysical objects as a function of the OM central pressure for the DM interaction strength parameter $y={10}^{-1}$ (left panels), and $y={10}^3$ (right panels). The vertical black and red dashed lines delimit the stable regions for two sets given by different $p_{\mathrm{DM}}/p_{\mathrm{OM}}$, denoted by black and red curves. Each curve in each set stands for a DM particle mass going from 1 GeV to 500 GeV (1, 5, 10, 50, 100, 200, 500) from top to bottom. In this figure black curves correspond to $p_{\mathrm{DM}}/p_{\mathrm{OM}}={10}^{-5}$, whereas red curves correspond to $p_{\mathrm{DM}}/p_{\mathrm{OM}}={10}^5$.

Figure 3

Same as in Fig. 2, for the dimensionless ratios, $p_{\mathrm{DM}}/p_{\mathrm{OM}}={10}^{-3}$ (black curves) and $10^3$ (red curves).

Figure 4

Same as in Fig. 2, for the dimensionless ratios, $p_{\mathrm{DM}}/p_{\mathrm{OM}}={10}^{-1}$ (black curves) and $10^1$ (red curves).

Figure 5

Total mass, $M_T$, and radius of OM content, $R_{\mathrm{OM}}$, of the astrophysical objects as a function of the central density of OM for the DM interaction strength parameters $y={10}^{-1}$ (left panels) and $y={10}^3$ (right panels). We fix $m_{\mathrm{DM}}=1\mathrm{GeV}$. The colored lines indicate solutions for $M_T$ and $R_{\mathrm{OM}}$ over OM central densities for a set of dimensionless ratio, $p_{\mathrm{DM}}/p_{\mathrm{OM}}$, running from ${10}^{-5}$ to $10^5$. These lines turn grey in the unstable regions. Note that for the case $y={10}^{-1}$, lines from $p_{\mathrm{DM}}/p_{\mathrm{OM}}={10}^{-1}$ to $p_{\mathrm{DM}}/p_{\mathrm{OM}}={10}^{-5}$ for the $M_T$ and $R_{\mathrm{OM}}$ distributions lie on top of each other.

Figure 6

Mass-radius relations of the equilibrium configuration of DM-admixed WD branch for weakly interacting DM, $y={10}^{-1}$. Results are shown for DM particle mass $m_{\mathrm{DM}}$ ranging from 1 to 500 GeV (1, 5, 10, 50, 100, 200, 500) from top to bottom. Each color corresponds to the DM particle mass, indicated in the legend. Each panel corresponds to a different $p_{\mathrm{DM}}/p_{\mathrm{OM}}$, indicated in the legend. Note that for some values of $p_{\mathrm{DM}}/p_{\mathrm{OM}}$, some mass curves are not visible because they overlap with others.

Figure 7

Same as in Fig. 6 for the NS branch.

Figure 8

Same as in Fig. 6 for the strongly interacting DM, $y={10}^3$.

Figure 9

Same as in Fig. 8 for the NS branch.

Figure 10

The total maximum mass of the CO as a function of the DM mass for weakly interacting DM, $y={10}^{-1}$. The colored curves, built from the extrema at fixed $p_{\mathrm{DM}}/p_{\mathrm{OM}}$ curves (see text) at a given DM particle mass, show the evolution of the star mass with increasing DM mass content. Each color corresponds to one DM particle mass, as indicated in legend. Top panel: The neutron-star branches. Bottom panel: The white-dwarf branches.

Figure 11

Same as Fig. 10 for the strongly interacting DM, $y={10}^3$. Note that lines shift horizontally to the left with increase of DM particle mass, while exhibiting a growth with increasing DM content for $m_{\mathrm{DM}}=1–10\mathrm{GeV}$.