Pair-instability supernova

A pair-instability supernova occurs when pair production, the production of free electrons and positrons in the collision between atomic nuclei and energetic gamma rays, temporarily reduces the internal pressure supporting a supermassive star's core against gravitational collapse. 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 black hole remnant behind. Pair-instability supernovae can only happen in stars with a mass range from around 130 to 250 solar masses and low to moderate metallicity (low abundance of elements other than hydrogen and helium – a situation common in Population III stars). The recently observed objects SN 2006gy, SN 2007bi, SN 2213-1745, and SN 1000+0216 are hypothesized to have been pair-instability supernovae. A pair-instability supernova occurs when pair production, the production of free electrons and positrons in the collision between atomic nuclei and energetic gamma rays, temporarily reduces the internal pressure supporting a supermassive star's core against gravitational collapse. 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 black hole remnant behind. Pair-instability supernovae can only happen in stars with a mass range from around 130 to 250 solar masses and low to moderate metallicity (low abundance of elements other than hydrogen and helium – a situation common in Population III stars). The recently observed objects SN 2006gy, SN 2007bi, SN 2213-1745, and SN 1000+0216 are hypothesized to have been pair-instability supernovae. Photons (the same particles that we perceive as light) 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 (hence the Stefan-Boltzmann law). The wavelength of maximum emission from a black body is inversely proportional to its temperature. That is, the frequency, and the energy, of the greatest population of photons of black-body radiation is directly proportional to the temperature. In very large hot stars with a temperature above about 3×108 K, photons produced in the stellar core are primarily in the form of gamma rays, with a very high energy level. The pressure from these gamma rays helps to support the upper layers of the star against the inward pull of gravity. If the level of gamma rays (the energy density) is suddenly reduced, then the outer layers of the star will begin to collapse inwards. Sufficiently energetic gamma rays can interact with nuclei, electrons, or one another. They can form pairs of particles, such as electron-positron pairs, and electron-positron pairs can also meet and annihilate each other to create gamma rays again, in accordance with Einstein's mass-energy equivalence equation E = mc2. At the very high density of a large stellar core, pair production and annihilation occur rapidly. Gamma rays, electrons, and positrons are overall held in thermal equilibrium, ensuring the star's core remains stable. 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 reduces the pressure. When the collapse stops, the positrons find electrons and the pressure from gamma rays is driven up, again. The population of positrons provides a brief reservoir of new gamma rays as the expanding supernova's core pressure drops.