Pair-instability supernova

[1] This pressure drop leads to a partial collapse, which in turn causes greatly accelerated burning in a runaway thermonuclear explosion, resulting in the star being blown completely apart without leaving a stellar remnant behind.

Photons given off by a body in thermal equilibrium have a black-body spectrum with an energy density proportional to the fourth power of the temperature, as described by the Stefan–Boltzmann law.

In very massive, hot stars with interior temperatures above about 300000000 K (3×108 K), photons produced in the stellar core are primarily in the form of very high-energy gamma rays.

The pressure from these gamma rays fleeing outward from the core helps to hold up the upper layers of the star against the inward pull of gravity.

By random fluctuation, the sudden heating and compression of the core can generate gamma rays energetic enough to be converted into an avalanche of electron-positron pairs.

This reduction in gamma ray energy density reduces the radiation pressure that resists gravitational collapse and supports the outer layers of the star.

When the temperature reaches the level when electrons and positrons carry the same energy fraction as gamma-rays, pair production cannot increase any further, it is balanced by annihilation.

Calculations suggest that so much of the outer layers are lost that the very hot core itself is no longer under sufficient pressure to keep it intact, and it is completely disrupted too.

These stars are large enough to produce gamma rays with enough energy to create electron-positron pairs, but the resulting net reduction in counter-gravitational pressure is insufficient to cause the core-overpressure required for supernova.

The collapse proceeds to efficiently compress the star's core; the overpressure is sufficient to allow runaway nuclear fusion to burn it in several seconds, creating a thermonuclear explosion.

In addition to the immediate energy release, a large fraction of the star's core is transformed to nickel-56, a radioactive isotope which decays with a half-life of 6.1 days into cobalt-56.

This endothermic (energy-absorbing) reaction absorbs the excess energy from the earlier stages before the runaway fusion can cause a hypernova explosion; the star then collapses completely into a black hole.