A pair-unstable supernova is the most powerful explosion that can occur in the universe. Someone might argue, «But wait, what about the Big Bang?» The thing is that the Big Bang was not an explosion in the usual sense of the word, and if it were my will, I would rename it the Big Expansion or something like that. The name «Big Bang» gives rise to many misconceptions associated with the perception of the big bang as a normal explosion. But back to the topic of the article.
As many know, when massive stars run out of fuel to support thermonuclear reactions, they explode in the form of supernovae. After explosions, a nebula with a black hole or neutron star in the center remains from the star.
However, many are unaware that there are different types of supernovae. One of these types —
As you know, photons are constantly being born inside the stars. Figuratively speaking, photons tend to escape from the star and press on its outer layers from the inside, generating internal pressure, but the outer layers are held by the star’s gravity.
The shape of a star in the form of a huge ball is precisely due to the fact where the internal pressure of photons comes into equilibrium with the gravity of the star. That is why stars increase in size over time: their mass and gravity decrease and internal pressure expands the star.
Pairs of particles and antiparticles (usually electrons and positrons) begin to be born inside pair-unstable stars.
This process is, in fact, the reverse of the process of annihilation of matter and antimatter. When two high-energy light beams collide, energy is converted into particles: an electron and a positron.
The result of this process is that fewer photons press on the outer layers of the star (after all, the photons have turned into particles and antiparticles). The star begins to shrink.
Compression raises the internal pressure and temperature inside the star. The hotter star emits more powerful gamma rays, which expand the star again and it cools slightly. Then again, due to the creation of particle-antiparticle pairs, the star contracts, and so on. It is because of the constant confrontation of these forces that the star is called
At some point, the star begins to collapse — the outer layers acquire a momentum that is too strong to be stopped by the pressure of photons increasing with increasing temperature.
This leads to the fact that the temperature and pressure rise to enormous values and the star burns all the fuel in just a few seconds. In a matter of moments, a huge mass of matter is converted into pure energy.
As a result, the most powerful explosion possible in the universe occurs, which is hundreds of times more powerful than the explosions of ordinary supernovae.
As a result of the explosion of a pair-unstable supernova, literally nothing remains, except for a certain amount of heavy elements formed in the course of thermonuclear reactions.
Explosions like this are very rare in the universe. Firstly, stars so large are not common, and secondly, stars should consist almost only of hydrogen and helium. The noticeable fraction of heavier elements in the star makes pairwise instability unlikely.
In history, there have been several cases of observation of outbursts that can be identified as pair-unstable supernovae.
In our galaxy, a candidate for an explosion as a pair-unstable supernova is Eta Carina A. It is located at a distance of 7,500 light years from the Sun, but if it explodes as a pair-unstable supernova, its light will be so bright that it will allow reading at night, and she herself will be visible in the sky as a second Sun for several weeks.
However, we are not sure that Eta Carina A will explode as a pair-unstable one. Perhaps the star will have time to lose enough mass before the explosion, and then there will be a type Ib or Ic supernova explosion. These are also quite powerful explosions and they will also be visible from the Earth with the naked eye, but much weaker than the potential explosion of a pair-unstable supernova.
Eta Carina A is expected to explode over the next several thousand years.