Can somebody explain what is "pair-production" when referring to energy being converted into mass.?

Answer 1

Large numbers of pairs of particles, an electron and a positron (an anti-matter version of an electron, having a + charge where an electron has a - charge) are produced in hypergiant stars as they turn into a supernova. And the sheer volume of pair production causes a runaway reaction which completely blows the star apart.

THE BRIGHTEST STELLAR EXPLOSION EVER RECORDED

This issue arose recently regarding the supernova SN 2006gy and it is thought that it could arise as regards the star Eta Carinae in our own galaxy.

SN 2006gy was an extremely energetic supernova, sometimes referred to as a hypernova, that was discovered around September 18, 2006.

On May 7, 2007, NASA and several of the astronomers announced the first detailed analyses of the supernova, describing it as the "brightest stellar explosion ever recorded".

SN 2006gy occurred in a distant galaxy (NGC 1260), approximately 238 million light years (72 megaparsecs) away. Therefore, due to the time it took light from the supernova to reach Earth, the event occurred about 238 million years ago.

Preliminary indications are that it was an unusually high-energy supernova of a very large star, around 150 solar masses, possibly of a type referred to as a pair instability supernova.

A pair instability supernova can only happen in stars that are very massive—having a range of around 130 to 250 solar masses.

The massive star's core can produce high energy gamma rays which have a greater energy than the rest mass of two electrons (mass-energy equivalence). These gamma rays interact with electromagnetic fields of the atomic nuclei in the star, and become particle and anti-particle pairs of electrons and positrons.

This causes the average travel distance of the gamma rays to become shorter, causing the temperature of the interior of the star to rise. This causes an even larger fraction of the produced gamma rays to be of high enough energy for pair production, causing more of the energy to be reabsorbed closer to its source.

This creates a runaway reaction. As the energy is concentrated more and more into the star's core, the outer layers start to fall inwards, which then compress the core. The compression and heating produce a rapid (few seconds) thermonuclear burn or explosion of the core material. The explosion blows the star completely apart without leaving a black hole remnant behind

ETA CARINAE

Eta Carinæ (η Carinæ or η Car) is a highly luminous hypergiant star located approximately 7,500 light years from Earth in the Milky Way galaxy.

Since Eta Carinæ is 32,000 times closer than SN2006gy, the light from it will be almost a billion-fold brighter. It is estimated to be similar in size to the star which became SN2006gy.

Dave Pooley, one of the discoverers of SN2006gy, says that if Eta Carinæ exploded in a similar fashion, it would be bright enough that one could read by its light here on Earth nights, and would even be visible during the day time.

SN2006gy's Apparent magnitude (m) is 15, so a similar event at Eta Carinæ will have an apparent magnitude of about -7.5, about 16 times as bright as Venus and about 250 times as bright as Sirius.

Answer 2

Electrons and positrons have masses of about 9 x 10^-31 kg which using E=mc^2 comes to 511 keV. A photon (gamma ray or high energy x-ray) of 1022 keV (1.022 MeV) or higher can produce an electron-positron pair.

Answer 3

It has to do with the particles that comprise the mass which is being created. They are charged, and would be created as 1 pair, one with a (+) charge and the other with a (-) charge.