the protoneutron star and the rest comes from its subsequent contraction. Astronomical observations, on the other hand, show the typical core-collapse supernova explosion energy to be in the range $10^{50}-10^{51}\,\mathrm{erg}$. *Hypernova* explosions may have up to $10^{52}\,\mathrm{erg}$, but they make up $\lesssim$1% of all core-collapse supernovae. A small subset of hypernovae are associated with gamma-ray bursts.

Where is all the gravitational energy going that does not contribute to the explosion energy? The answer is: Neutrinos. Antineutrinos and neutrinos of all flavors carry away $\gtrsim 99\%$ ($\gtrsim 90\%$ in the hypernova case) of the available energy over $\mathcal{O}(10)\,\mathrm{s}$ as the protoneutron star cools and contracts. This was first theorized and then later observationally confirmed with the detection of neutrinos from SN 1987A, the most recent core-collapse supernova in the Milky Way vicinity.

![Volume rendering of the specific entropy in the core of a neutrino-driven core-collapse supernova at the onset of explosion. Based on the 3D general-relativistic simulations of [@ott:13a] and rendered by Steve Drasco (Cal Poly San Luis Obispo). Specific entropy is a preferred quantity for visualization, since in the core of a supernova, it typically ranges from $\sim$1 to $\sim$20 units of Boltzmann’s constant $k_\mathrm{B}$ per baryon. Shown is the 