SN 2006gy and Pair Instability Supernovae

Like explosions? Well, supernovae are the biggest ones in the whole universe. Some can outshine their entire host galaxy and last week, astronomers observed their biggest one yet, called SN 2006gy.


SN 2006gy is the bright spot on the right. It's entire host galaxy is the darkish green blur one the left.

It came from a star more than 150 times the mass of our sun. It is an example of a very rare type of supernova called a pair instability supernova. In these kinds of supernova a high energy photon (gamma ray) coming from the fusion areas within the star spontaneously forms a particle anti-particle pair and is either deflected in a different direction when the two particles collide or not recreated at all, thus reducing the light pressure on the surface of the star. This allows gravitational forces to win out on the surface of the star, causing it to contract.


An illustration of the mechanisms involved in pair instability supernova.

When the gammas produce pairs of particles, they travel less on average, thus heating the innards of the star, thus causing it to produce more gammas. The process goes on until the core of the star explodes with more force than the gravity that holds the star together. This can only occur in stars with more than 130 times the mass of the sun. In lesser massed stars, the process may even out and lead to a semi-stable, pulsating star. In the big stars though, it can produce what we saw with SN 2006gy, namely, an enormous bang: