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Pair instability supernovae occur in massive stars with low metallicity. The core’s high energy creates electron-positron pairs, leading to a pressure drop and partial collapse. The resulting thermal energy blows the star apart completely, leaving no remnants. Eta Carinæ could potentially explode in a pair-instability supernova, visible both day and night.
A pair instability supernova is a special type of supernova, or stellar explosion, that occurs only in very massive stars (between 130 and 250 solar masses), with low to moderate rotational rates, and low metallicity (mostly made up of hydrogen and helium). ). In a pair-instability supernova, the core of the star is so highly energetic that collisions between gamma rays and atomic nuclei cause the spontaneous creation of electron-positron pairs, siphoning off much of the thermal energy and leading to a drop in pressure. This pressure drop causes the star to partially collapse due to gravity.
Collapse regions are rapidly superheated to extreme temperatures and pressures, causing atomic nuclei to rapidly melt and release enormous energy. The resulting thermal energy is so great that it blows the star apart completely, leaving nothing behind. All other supernovae leave behind remnants of black holes or neutron stars.
Pair-instability supernovae are thought to be rare today, with only one candidate noted in recent astronomical history: SN 2006gy, which has been called “the brightest stellar explosion on record.” It was ten times more powerful than a supernova and, like other supernova explosions, was called a hypernova. Some scientists have proposed that supernovae with pair instability could leave a quark star remnant, but this is unconfirmed.
Although pair-instability supernovae are rarely observed in the present, they are thought to have been very numerous in the distant past, among primordial, supermassive, low-metallicity Population III stars. These are the first stars to be born after the 100-million-year dark period following the Big Bang. They are sufficiently old and distant to be virtually undetectable using our current telescope technology, although the James Webb Space Telescope has imaged the 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 could explode in a pair-instability supernova at the end of its life. Being only 4,500 light-years away from 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 also be visible during the day, like the Moon. Fortunately, it still wouldn’t be energetic enough to significantly damage Earth’s atmosphere.
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