Pair-instability supernova

A pair-instability supernova is a catastrophic stellar explosion that completely destroys a star. While most massive stars leave behind a dense remnant like a neutron star or a black hole, this specific event leaves nothing behind. The entire mass of the star is ejected into space. This happens because the energy released during the explosion is greater than the star's gravitational binding energy. This process is driven by a sudden loss of internal pressure within the star's core.

To understand this, we must look at how massive stars maintain stability. In extremely hot and massive stars, the core produces high-energy light called gamma rays. These photons create radiation pressure, which acts as an outward force. This pressure is essential because it resists the inward pull of gravity. In these specific stars, the core temperatures are high enough for gamma rays to interact with atomic nuclei. When these collisions occur, they trigger pair production, which is the creation of electron-positron pairs.

This pair production creates a dangerous feedback loop. As gamma rays are converted into electron-positron pairs, the radiation pressure drops. This reduction in pressure allows gravity to compress the core further. As the core contracts, it becomes much hotter and denser. This heating increases the energy of the produced gamma rays. Higher energy gamma rays are even more likely to undergo pair production. This creates a runaway process where the core loses its outward support at an accelerating rate.

Eventually, this collapse leads to a massive thermonuclear explosion. The rapid compression ignites the detonation fusion of oxygen and other heavy elements. This happens in a matter of seconds. The sudden surge in power production is so immense that it overcomes the star's gravity. Unlike other types of stars, the core of a pair-instability supernova is completely disrupted. This means the star is blown apart entirely, leaving no central object behind.

Not all large stars explode this way. The outcome depends heavily on the star's initial mass and its metallicity. Metallicity refers to the abundance of elements heavier than hydrogen and helium. For a true pair-instability supernova to occur, a star generally needs a mass between 130 and 250 solar masses. It also requires low to moderate metallicity, a condition often found in Population III stars. If a star is between 100 and 130 solar masses, it might experience pulses instead of a single explosion. Stars with 250 solar masses or more undergo a different process called photodisintegration, which leads to a black hole.

These explosions are among the most luminous events in the universe. For the most massive progenitor stars, the peak luminosity can exceed 10^44 ergs per second. This makes them even brighter than Type Ia supernovae. The light curves of these events are highly extended, meaning the peak brightness occurs months after the explosion begins. This delay is caused by the extreme amount of ejected mass and the dense nature of the debris.

A notable example of this phenomenon is the hypernova known as SN 2006gy. Studies suggest that approximately 40 solar masses of the original star were released during this event. Much of the visible light from such explosions comes from the radioactive decay of newly created elements. Specifically, the explosion transforms a large portion of the core into nickel-56. This radioactive isotope decays into cobalt-56, which then decays into stable iron-56.

Because these stars are completely destroyed, they contribute significantly to the chemistry of the universe. They eject many solar masses of heavy elements into interstellar space. These elements eventually become part of new stars and planetary systems. This process also helps explain the "upper mass gap" in the distribution of stellar black holes. Since these stars leave no remnant, there is a lack of black holes in the specific mass range associated with these explosions.