Black Hole Formation Accompanied by the Supernova Explosion of a 40 M _⊙ Progenitor Star

We have simulated the collapse and evolution of the core of a solar-metallicity 40 M _⊙ star and find that it explodes vigorously by the neutrino mechanism, despite its very high “compactness.” Within ∼1.5 s of explosion, a black hole forms. The explosion is very asymmetrical and has a total explosion energy of ∼1.6 × 10⁵¹ erg. At black hole formation, its baryon mass is ∼2.434 M _⊙ and gravitational mass is 2.286 M _⊙. Seven seconds after black hole formation, an additional ∼0.2 M _⊙ is accreted, leaving a black hole baryon mass of ∼2.63 M _⊙. A disk forms around the proto−neutron star, from which a pair of neutrino-driven jets emanates. These jets accelerate some of the matter up to speeds of ∼45,000 km s⁻¹ and contain matter with entropies of ∼50. The large spatial asymmetry in the explosion results in a residual black hole recoil speed of ∼1000 km s⁻¹. This novel black hole formation channel now joins the other black hole formation channel between ∼12 and ∼15 M _⊙ discovered previously and implies that the black hole/neutron star birth ratio for solar-metallicity stars could be ∼20%. However, one channel leaves black holes in perhaps the ∼5-15 M _⊙ range with low kick speeds, while the other leaves black holes in perhaps the ∼2.5-3.0 M _⊙ mass range with high kick speeds. However, even ∼8.8 s after core bounce the newly formed black hole is still accreting at a rate of ∼2 × 10⁻² M _⊙ s⁻¹, and whether the black hole eventually achieves a significantly larger mass over time is yet to be determined.