Matter, and therefore everything seen, is made out of fundamental particles of nature. These fundamental particles are hadrons and leptons, the hadrons being further subdivided into baryons and mesons. Hadrons include the proton and neutron and leptons include the electron, muon and tau as well as the corresponding neutrinos. For simplicity, the overwhelming majority of matter in the universe is comprised of protons, neutrons and electrons.
These particles have been mysterious for quite some time: although physicists knew they existed, they knew very little about them. In physics, you can say you "know" something when, among other proprieties, you can predict and describe the way it behaves. You know that a stone will fall if it's not held properly. Physicists can describe how it falls and predict exactly where it will touch the ground using mathematical formulas.
But physicists couldn't predict anything about the electron! Until a Paul Dirac thought about it: he found a very simple way to describe the proprieties and behavior of electrons, but... there was something curious about it. His description would only work if the electron had a "twin" particle, identical to it but with an opposite electric charge. It would be just like its mirror image! He called it an antielectron or POSITRON. Of course, the same would be true for any existing particle (proton and antiproton, neutron and antineutron).
Of course, to make matter a lot of it is needed, and very much concentrated in space. Particles and antiparticles are always created together, out of energy.
The first success was the creation of an "electron-positron" pair, twins that only require a relatively small amount of energy-dough to make them. Later came pairs of protons and antiprotons, then pairs of neutrons and antineutrons.
Antiparticles created in a laboratory "live" for a very short time before they crash into normal particles and annihilate. But nevertheless, they do exist.
Paul Dirac wondered, if protons, electrons and neutrons stick together to make atoms, and atoms stick together to make everything around us, what we call matter, then what about positrons, antiprotons and antineutrons? Do they stick together to make antiatoms? Are antiatoms the building bricks of antimatter? Modern-day physicists agree with him. But thinking something is possible doesn't mean it's necessarily true.
Scientists are hard at work on this mystery at a place called CERN they are trying to build antimatter. If some of the originally-created antiparticles are still around, they certainly can't be nearby some people think those antiparticles could be somewhere far, far away in the Universe. Some people think the antiparticles do not exist anymore. Something may have happened, just after their creation, which destroyed them all, leaving only particles for the hard task of building up the Universe.
When a particle meets its antiparticle, they destroy each other, releasing a burst of energy such as gamma rays. In 1978, gamma ray detectors flown on balloons detected a type of gamma ray emerging from space that is known to be emitted when electrons collide with positrons — meaning there was antimatter in space.
These gamma rays apparently came from a cloud of antimatter roughly 10,000 light-years across surrounding our galaxy's core. This giant cloud shines brightly with gamma rays, with about the energy of 10,000 suns.
What exactly generated the antimatter was a mystery for the following decades. Suspects have included everything from exploding stars to dark matter.
Now, an international research team looking over four years of data from the European Space Agency's International Gamma Ray Astrophysics Laboratory (INTEGRAL) satellite has pinpointed the apparent culprits. Their new findings suggest these positrons originate mainly from stars getting devoured by black holes and neutron stars.
As a black hole or neutron star destroys a star, tremendous amounts of radiation are released. Just as electrons and positrons emit the tell-tale gamma rays upon annihilation, so too can gamma rays combine to form electrons and positrons, providing the mechanism for the creation of the antimatter cloud, scientists think.
The researchers calculate that a relatively ordinary star getting torn apart by a black hole or neutron star orbiting around it — a so-called "low mass X-ray binary" — could spew on the order of one hundred thousand billion billion billion billion positrons (a 1 followed by 41 zeros) per second. These could account for a great deal of the antimatter that scientists have inferred, reducing or potentially eliminating the need for exotic explanations such as ones involving dark matter.