Pair production

Light can turn into tiny bits of matter.

This happens when light has a lot of energy. The light hits a tiny center of an atom. This makes two small pieces.

One piece is a twin of the other. But they are opposites. If one has a plus charge, the other has a minus charge.

This can happen near a big star. It can even happen near a black hole.

It is amazing that light can become stuff!

Light can turn into matter. This is called pair production.

It starts with a photon. A photon is a tiny bit of light. To make this happen, the light must have a lot of energy. It must have more energy than the mass of the two new pieces.

The light must also be near an atomic nucleus. A nucleus is the center of an atom. This helps the light follow rules of energy and motion.

When the light hits the nucleus, it makes two new particles. One is a particle. The other is an antiparticle. They are like twins, but they are opposites. If one has a plus charge, the other has a minus charge.

Scientists can see this happen. In 2008, a large laser made many pairs at once. This can also happen in space. Near a black hole, gravity can pull these pairs apart. One piece escapes, but the other stays. This is part of a theory called Hawking radiation.

Pair production helps us understand how the universe works.

Light can actually turn into matter through a process called pair production.

This happens when a neutral boson, like a photon, creates two new particles. One is a subatomic particle and the other is its antiparticle. These two particles are like opposites of each other. For example, one might have a positive charge while the other has a negative charge. This process is a key way that light interacts with matter. It shows us how energy can change into physical things.

To make this work, the light must follow strict rules of physics. First, the incoming photon must have enough energy. This energy must be higher than the total rest mass energy of the two new particles. For an electron and a positron, this energy threshold is 1.022 MeV.

Second, the photon must be near an atomic nucleus. The nucleus helps the process follow the laws of energy and momentum. Without the nucleus, the particles could not satisfy both rules at once. When this happens, the nucleus often receives a small amount of recoil.

Scientists first observed these interactions using special tools. They used a device called a counter-controlled cloud chamber. This work was done by a scientist named Patrick Blackett. His discoveries were so important that he won the Nobel Prize in Physics in 1948.

Since then, we have learned much more about how particles behave. We now use complex math called quantum electrodynamics to study these events. This helps us understand the tiny diagrams that show how particles move.

There are many different types of pairs that can be made. You might see an electron and a positron pair. You could also see a muon and an antimuon pair. Even protons and antiprotons can be created this way.

In 2008, scientists used the Titan laser to make many pairs at once. They aimed the laser at a gold target that was 1 millimeter thick. This experiment showed how much energy is needed to create these particles in large numbers.

Pair production helps explain some of the biggest mysteries in space. Some scientists think it plays a role in Hawking radiation near black holes. In this theory, particle pairs constantly appear and disappear in a quantum foam. Strong gravity can pull these pairs apart before they can vanish. One particle might escape while the other is caught by the black hole.

It might also cause a special kind of stellar explosion called a pair-instability supernova. One example of this is the supernova known as SN 2006gy.

Pair production is a fascinating physical process where a neutral boson creates a subatomic particle and its corresponding antiparticle.

This phenomenon is a fundamental way that energy transforms into matter. While many types of pairs can form, the term often specifically describes a photon creating an electron and a positron. Other examples include the creation of a muon and an antimuon, or a proton and an antiproton. This process is a key interaction in particle physics because it demonstrates how energy and matter are deeply linked.

For pair production to occur, the laws of physics impose very strict constraints. The process must follow the conservation of energy and the conservation of momentum. Additionally, all other conserved quantum numbers must sum to zero. These numbers include angular momentum, electric charge, and lepton number. Because of this, the two new particles must have opposite values for these properties. If one particle has an electric charge of +1, its partner must have a charge of -1. If one has a strangeness of +1, the other must have a strangeness of -1.

The mechanism requires a specific amount of incoming energy. The energy of the incoming photon must be above a certain threshold. This threshold is at least the total rest mass energy of the two particles being created. For an electron-positron pair, this threshold is 1.022 MeV. This value is the sum of the rest mass energies of one electron and one positron, which is 2 × 511 keV. Because of this requirement, pair production does not happen in medical X-ray imaging. Those X-rays only contain about 150 keV, which is far below the needed threshold.

A photon cannot undergo pair production in empty space. It must be near an atomic nucleus to satisfy the conservation of momentum. When the photon interacts near a nucleus, the nucleus receives a small amount of recoil. This recoil helps balance the momentum of the system. In most cases, this recoil is small compared to the photon's energy. Because of this, the electron and positron are typically emitted in nearly the same direction. This is known as being nearly collinear.

The probability of this interaction happening depends on several factors. The chance of pair production increases as the photon energy increases. It also increases based on the atomic number of the nearby atom. Specifically, the probability increases approximately as the square of the atomic number, which is the number of protons. At high photon energies, such as the MeV scale and higher, pair production becomes the dominant way photons interact with matter. Scientists use quantum electrodynamics and Feynman diagrams to calculate the exact cross section, or the probability, of these interactions.

The history of this discovery is tied to important scientific milestones. These interactions were first observed using a counter-controlled cloud chamber. This device was used by the scientist Patrick Blackett. His work with these interactions led to him receiving the 1948 Nobel Prize in Physics. In modern laboratory settings, scientists continue to study these events. In 2008, researchers used the Titan laser to generate many positron-electron pairs. They achieved this by aiming the laser at a gold target that was only 1 millimeter thick.

Pair production also helps scientists understand massive events in the universe. It is used in the heuristic explanation of hypothetical Hawking radiation. In this theory, particle pairs constantly appear and disappear in a "quantum foam." Near a black hole, strong gravitational tidal forces may pull these pairs apart. One particle might escape while its antiparticle partner is captured by the black hole. Pair production is also linked to a type of stellar explosion called a pair-instability supernova. In these stars, pair production lowers the internal pressure, leading to a partial implosion and then an explosive thermonuclear burning. The supernova SN 2006gy is hypothesized to be one such event.