An international team of astrophysicists led by Peter Garnavich, professor of astrophysics at the University of Notre Dame, has caught two supernovae in the act of exploding. Using the Kepler Space Telescope, the team spent three years observing 50 trillion stars for the chance to watch as supersonic shockwaves reached their surfaces after explosions deep in the core. For the first time, a "shock breakout" in an exploding supergiant star was discovered at visible wavelengths.

Stars 10 to 20 times the mass of our sun often puff up to supergiants before ending their lives as supernovae. These stars are so large that the Earth's orbit would easily fit inside such a star. When these massive stars run out of fuel in their center, their core collapses down to a neutron star and a supersonic shockwave is sent out to blow up the entire star.

When the shockwave reaches the surface of the star, a bright flash of light, called a "shock breakout," is predicted.

"The flash from a breakout should last about an hour, so you have to be very lucky or continuously stare at millions of stars just to catch one flash," said Garnavich.

In 2011, two of these massive red supergiants exploded while in Kepler's view. The first, KSN 2011a, is nearly 300 times the size of our sun and a mere 700 million light years from Earth. The second, KSN 2011d, is roughly 500 times the size of our sun and some 1.2 billion light years away.

Supernovae like these - known as Type II - begin when the internal furnace of a star runs out of nuclear fuel causing its core to collapse as gravity takes over.

Understanding the physics of these explosions allows scientists to better understand how the seeds of chemical complexity and life itself have been scattered in space and time in the Milky Way galaxy.

The Kepler Space Telescope is famous for its discoveries of extra-solar planets, some that may have the right conditions to harbor life. But Kepler can also look at galaxies beyond the Milky Way. A team of astrophysicists from Notre Dame, Maryland, Berkeley and Australia have formed the "Kepler ExtraGalactic Survey," or KEGS, specifically to apply the power of Kepler to study galaxies and supernovae.

The research paper reporting this discovery has been accepted for publication in the Astrophysical Journal and can be found here