'We Don't Planet' Episode 15: How Type II Supernovae Are Triggered

When a core of iron forms in the center of a sufficiently massive star, the continued gravitational collapse of the surrounding layers initiates a staggeringly large explosion — a Type II supernova. But the exact mechanisms behind these explosions are still shrouded in mystery.

The first problem is that the "bounce" of material off the core isn’t sufficiently powerful enough to further eject material. A shock wave forms in the inner core region and begins to propagate outward, but it slows down and eventually stalls about midway through the star.

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The shock is revived by a sudden influx of neutrinos, which are formed when electrons are shoved into protons to form neutrons in the iron core. Since neutrinos do not interact via the electromagnetic force, they usually pass through other matter without notice. But they do participate in the weak nuclear force and can occasionally scatter off another particle. A sufficient number of neutrinos — such as produced in the core at the beginning stages of a supernova — can exert a pressure on the surrounding material.

The shock wave gets reinvigorated by the neutrinos, but they quickly lose energy, and once again the shock stalls out. This is where things get a little hazy. But advanced computer simulations suggest that at this stage the interior of the star becomes highly unstable, and some vibrational modes become enhanced. Continually reinforced, the oscillations grow in amplitude, eventually destroying the star in an asymmetrical fashion, finally completing the supernova explosion.

"We Don't Planet" is hosted by Ohio State University astrophysicist and COSI chief scientist Paul Sutter with undergraduate student Anna Voelker. Produced by Doug Dangler, ASC Technology Services. Supported by The Ohio State University Department of Astronomy and Center for Cosmology and AstroParticle Physics. You can follow Paul on Twitter and Facebook.