Dark Matter and the First Stars: A New Phase of Stellar Evolution

A mechanism is identified whereby dark matter (DM) in protostellar halos dramatically alters the current theoretical framework for the formation of the first stars. Heat from neutralino DM annihilation is shown to overwhelm any cooling mechanism, consequently impeding the star formation process and possibly leading to a new stellar phase. A “dark star” may result: a giant ($\gtrsim 1\mathrm{AU}$) hydrogen-helium star powered by DM annihilation instead of nuclear fusion. Observational consequences are discussed.

Figure 1

Adiabatically contracted DM profiles for (a) an initial NFW profile and (b) an initial Burkert profile, for $M_{\mathrm{vir}}={10}^6{M}_{\odot }$, $c_{\mathrm{vir}}=10$, and $z=19$. The solid (blue) lines show the initial profile. Dot-dashed (black) lines correspond to a baryonic core density $n\sim {10}^7{\mathrm{cm}}^{-3}$, long-dashed (red) lines to ${10}^{10}{\mathrm{cm}}^{-3}$, dashed (magenta) lines to ${10}^{13}{\mathrm{cm}}^{-3}$, and dotted (green) lines to ${10}^{16}{\mathrm{cm}}^{-3}$.

Figure 2

Comparison of critical temperature [dashed (red) lines] to typical evolution tracks in the temperature-density phase plane. The solid (blue) and dotted (green) lines show the protostellar gas evolution from simulations of 21, 29, respectively. The dashed (red) lines mark $T_c(n)$ for (i) $m_{\chi }=1\mathrm{GeV}$ with ${\mathrm{H}}_2$ density from simulations, (ii) $m_{\chi }=1\mathrm{GeV}$ assuming 100% ${\mathrm{H}}_2$, (iii) $m_{\chi }=100\mathrm{GeV}$, and (iv) $m_{\chi }=10\mathrm{TeV}$. At the crossing point of the solid (blue) or dotted (green) and dashed (red) lines, DM heating dominates over cooling in the core’s evolution.