Pair-Instability Supernovas

Artist's Concept: A close-up of SN 2006gy (NASA/CXC/M.Weiss)

For extremely massive stars, another, even more violent type of supernova is possible. According to stellar evolution theory, temperatures rise to several billion degrees in the central regions of stars with masses between 140 and 260 suns. At these temperatures the usual process of converting mass into energy (E = mc²) by nuclear reactions is reversed, and energy is converted into mass in the form of pairs of electrons and antielectrons, or positrons.

The production of electron-positron pairs saps energy from the core of the star, disturbing the equilibrium between the outward push of pressure and the inward crush of gravity. This so-called "pair instability" causes violent pulsations that eject a large fraction of the outer layers of the star, and eventually disrupt the star completely in a thermonuclear explosion.

Illustration of Stellar Explosion of SN 2006gy (NASA/CXC/M.Weiss)

Pair-instability supernovas, if they exist, would be the most energetic thermonuclear explosions in the universe. In stars with masses greater than about 260 suns, the pulsations would be overwhelmed by gravity and the star would collapse to form a black hole without an explosion.

For stars with initial masses above about 200 suns, pair-instability supernovas would produce an abundance of radioactive nickel. Radioactive decay of this large mass of nickel into cobalt and other nuclei would feed energy into the expanding debris for several months, and create an ultra-bright supernova.

Observations with Chandra and optical telescopes indicate that Supernova 2006gy, the most luminous supernova ever recorded, may be a long-sought (40 years) pair-instability supernova.