The Biggest Explosions in the Universe. II
  One of the leading contenders for the origin of supermassive black holes at
$z \gtrsim$ 7 is catastrophic baryon collapse in atomically-cooled halos at $z
\sim$ 15. In this scenario, a few protogalaxies form in the presence of strong
Lyman-Werner UV backgrounds that quench H$_2$ formation in their constituent
halos, preventing them from forming stars or blowing heavy elements into the
intergalactic medium prior to formation. At masses of 10$^ 8$ \Ms\ and virial
temperatures of 10$^4$ K, gas in these halos rapidly cools by H lines, in some
cases forming 10$^4$ - 10$^6$ \Ms\ Pop III stars and, a short time later, the
seeds of supermassive black holes. Instead of collapsing directly to black
holes some of these stars died in the most energetic thermonuclear explosions
in the universe. We have modeled the explosions of such stars in the dense
cores of line-cooled protogalaxies in the presence of cosmological flows. In
stark contrast to the explosions in diffuse regions in previous simulations,
these SNe briefly engulf the protogalaxy but then collapse back into its dark
matter potential. Fallback drives turbulence that efficiently distributes
metals throughout the interior of the halo and fuels the rapid growth of
nascent black holes at its center. The accompanying starburst and x-ray
emission from these line-cooled galaxies easily distinguish them from more
slowly evolving neighbors and might reveal the birthplaces of supermassive
black holes on the sky.
