Pair-instability supernova

Some stars are very big.

Inside these stars, bright light pushes out. This light fights the pull of gravity.

Sometimes, that light turns into tiny bits of matter. This makes the light push less. Now, gravity pulls the star inward. The star falls in on itself. This makes the core very hot. It gets so hot that the star blows up!

The whole star is gone. It leaves nothing behind.

Some stars are truly massive. A pair-instability supernova is a giant explosion of these stars.

Inside a very hot star, light moves outward. This light is made of gamma rays. These rays create pressure. This pressure helps hold up the star against gravity.

In very big stars, something strange happens. High-energy gamma rays hit each other. They turn into tiny bits of matter called electron-positron pairs. This process uses up the light. Because the light is gone, the outward pressure drops.

Now, gravity pulls the star inward. The star collapses. This makes the core very hot and tight. The heat starts a runaway reaction. This is a fast way of burning fuel. It creates a huge explosion. The star blows apart completely. It does not leave a black hole behind. It leaves nothing at all. This happens to stars with 130 to 250 times the mass of our Sun. They must also have low metallicity. This means they have few elements besides hydrogen and helium.

A pair-instability supernova is a massive explosion that completely destroys a star. Most stars leave something behind when they die, like a black hole or a neutron star. However, this specific kind of explosion is so powerful that nothing is left. The entire star is blown apart into space.

This event happens to only the most enormous stars in our universe. It is a special way for a giant star to end its life.

To understand this, we must look at how a star stays stable. Inside a very hot, massive star, high-energy light called gamma rays moves outward. This light creates radiation pressure. This outward pressure fights against the inward pull of gravity. In these huge stars, gamma rays can hit atomic nuclei. This collision creates tiny bits of matter called electron-positron pairs. This process, known as pair production, uses up the gamma ray energy.

Because the energy is used to make these pairs, the outward pressure drops suddenly.

Once the pressure drops, gravity wins the fight. The star's core begins to collapse inward. This collapse makes the core much hotter and tighter. The heat causes the star to burn its fuel at a runaway rate. This is a very fast thermonuclear explosion. It happens so quickly that it can burn oxygen and other elements in just a few seconds. The energy from this explosion is greater than the gravity holding the star together.

The star is then completely disrupted by the power.

Scientists use math to predict which stars will explode this way. A star must be between 130 and 250 solar masses to do this. A solar mass is the mass of our own Sun. These stars also need low metallicity. This means they have very few elements other than hydrogen and helium. If a star is even larger, at 250 solar masses or more, it might collapse into a black hole instead.

This is because a different process called photodisintegration absorbs the energy.

We can see the results of these explosions in space. One famous example is the hypernova known as SN 2006gy. In that case, about 40 solar masses of the star were released. These explosions can be much brighter than other types of supernovae. They also create many heavy elements like nickel-56. This nickel decays into cobalt-56 and then into iron-56. These elements are scattered into space to become part of new things.

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.