A pair-instability supernova is a special type of supernova, or stellar explosion, occurring only in stars which are very massive (between 130 and 250 solar masses), have low to moderate rotation rates, and low metallicity (primarily made of hydrogen and helium). In a pair-instability supernova, the star's core is so extremely energetic that collisions between gamma rays and atomic nuclei result in the spontaneous creation of electron-positron pairs, siphoning away much of the thermal energy and leading to a drop in pressure. This pressure drop results in the star partially collapsing due to gravity.
Collapse regions are quickly superheated to extreme temperatures and pressures, causing the rapid fusion of atomic nuclei and tremendous energy release. The resulting thermal energy is so huge that it blows the star completely apart, leaving behind nothing behind. All other supernovae leave behind black hole or neutron star remnants.
Pair-instability supernovae are thought to be rare today, with only one candidate noted in recent astronomical history: SN 2006gy, which was called "the brightest stellar explosion ever recorded." It was ten times more powerful than a supernova, and like other like supernovae explosions was referred to as a hypernova. Some scientists have proposed that pair-instability supernovae might leave behind a quark star remnant, but this is unconfirmed.
Although pair-instability supernovae are rarely observed in the present, it is thought that they were very numerous in the distant past, among the primordial, supermassive, low-metallicity Population III stars. These are the first stars to come into being after the 100 million year period of darkness following the Big Bang. They are sufficiently old and distant to be practically unobservable using our current telescope technology, although the James Webb Space Telescope has imaged ancient light thought to be the faint glow of Population III stars.
Eta Carinæ is a star in our galaxy with so much mass (100-150 solar masses) that it may explode in a pair-instability supernova at the end of its life. Being only 4,500 light years away from the Earth, if it were to explode, it would be so bright that it would be possible to read at night using its light. The supernova would even be visible during the day, like the Moon. Fortunately, it would still not be energetic enough to significantly damage Earth's atmosphere.