Muon Creation in Supernova Matter Facilitates Neutrino-Driven Explosions

Muons can be created in nascent neutron stars (NSs) due to the high electron chemical potentials and the high temperatures. Because of their relatively lower abundance compared to electrons, their role has so far been ignored in numerical simulations of stellar core collapse and NS formation. However, the appearance of muons softens the NS equation of state, triggers faster NS contraction, and thus leads to higher luminosities and mean energies of the emitted neutrinos. This strengthens the postshock heating by neutrinos and can facilitate explosions by the neutrino-driven mechanism.

Figure 1

Upper row: Angle-averaged shock radii (solid line) and mass-infall rates (at 400 km, dashed line) versus postbounce time for our sets of models with SFHo (left) and LS220 EOS (right). Lower row: Time evolution of NS radii (measured at an average density of $10^{11}\mathrm{g}{\mathrm{cm}}^{-3}$, left) and net heating rate integrated over the gain layer (in $1\mathrm{B}{\mathrm{s}}^{-1}={10}^{51}\mathrm{erg}{\mathrm{s}}^{-1}$, right) for models with SFHo EOS.

Figure 2

Evolution of angle-averaged specific entropy (color, in $k_B$ per nucleon) versus postbounce time for model s20.0-SFHo with our standard physics (top) and with muons (bottom). The outer boundary of the light blue-green-yellow region follows the average radius of the SN shock. The gray lines mark “mass shells” (radii of constant enclosed baryonic mass), the white line corresponds to an average density of $10^{11}\mathrm{g}{\mathrm{cm}}^{-3}$.

Figure 3

Neutrino luminosities (upper row) and radiated mean neutrino energies (defined as ratio of neutrino energy density to number density, lower row) versus postbounce time, evaluated in the laboratory frame at the average gain radius for the standard model with SFHo EOS (black) and the simulation with muons (red).

Figure 4

Top: Radial profiles at 0.4 s after bounce of the net numbers of charged leptons (left-hand scale) and neutrinos (right-hand scale) per baryon for the standard model with SFHo EOS (solid lines) and the simulation with muons (dashed lines). Bottom: Radial profiles of density (black lines) and temperature (red lines) for three cases with SFHo EOS.