Probing the metastability of a protoneutron star with hyperons in a core-collapse supernova

The role of $\Lambda$ hyperons is investigated in the dynamical collapse of a nonrotating massive star to a black hole using a one-dimensional general-relativistic (gr1d) code. The dynamical formation and evolution of a protoneutron star (PNS) to a black hole is followed using various progenitor models, adopting a hyperonic equation of state (EoS) generated by Shen et al. [Shen, Toki, Oyamatsu, and Sumiyoshi, Astrophys. J., Suppl. Ser. 197, 20 (2011)]. The results are compared with those of a nuclear EoS by Shen et al. [Shen, Toki, Oyamatsu, and Sumiyoshi, Nucl. Phys. A 637, 435 (1998)] to understand the role of $\Lambda$ hyperons in the core-collapse supernova. The neutrino signals that may be used as a probe for core collapse is also discussed. Further, an exotic EoS may support a cold neutron star with a maximum mass much lower than that of a PNS. In this regard, the metastability of a PNS in the presence of $\Lambda$ hyperons is studied in the long-time evolution of the progenitors, relevant to supernova SN1987A.

Figure 1

Temporal evolution of baryonic and gravitational mass for the Shen $np$ and $np\Lambda$ EoS.

Figure 2

Temporal evolution of central density for the Shen $np$ and $np\Lambda$ EoS.

Figure 3

Temporal evolution of temperature for teh Shen $np$ and $np\Lambda$ EoS.

Figure 4

Density profile of the 40$M_{\odot }$ (black lines) and 23$M_{\odot }$ (red/gray lines) progenitors with $np$ [panel (a)] and $np\Lambda$ [panel (b)] EoS at $t=t_{\mathrm{bounce}}$ and at postbounce times of 0.363 and 0.563 s.

Figure 5

Temperature profile of the 40$M_{\odot }$ (black lines) and 23$M_{\odot }$ (red/gray lines) progenitors with $np$ [panel (a)] and $np\Lambda$ [panel (b)] EoS at $t=t_{\mathrm{bounce}}$ and at postbounce times of 0.363 and 0.563 s.

Figure 6

Mass fractions of the constituents for the 40$M_{\odot }$ (black lines) and 23$M_{\odot }$ (red/gray lines) progenitors with the Shen $np\Lambda$ EoS.

Figure 7

Snapshots of mass fractions of the constituents vs radius at $t=0.363$ s (black lines) and 0.563 s (red/gray lines) postbounce for the 40$M_{\odot }$ progenitors (a) and $t=0.363$ s (black lines) and 0.84 s (purple/gray lines) postbounce for the 23$M_{\odot }$ progenitors (b) with the Shen $np\Lambda$ EoS.

Figure 8

Evolution of shock radii for the $23M_{\odot }$ progenitor models.

Figure 9

Long-time evolution of central density for the $23M_{\odot }$ progenitor model with teh $np\Lambda$ EoS.

Figure 10

Long-time evolution of temperature for the $23M_{\odot }$ progenitor model with teh $np\Lambda$ EoS.

Figure 11

Long-time evolution of gravitational mass for the $23M_{\odot }$ progenitor model with teh $np\Lambda$ EoS. The dark solid line is with $f_{\mathrm{heat}}=1$ for the $40M_{\odot }$ progenitor, and the rest of the lines are for the $23M_{\odot }$ progenitor.