Antimatter or contra-terrene matter (HS: di'mok) is matter that is composed of the antiparticles of those that constitute normal matter. If a particle and its antiparticle come in contact with each other, the two annihilate and produce a burst of energy, which results in the production of other particles and antiparticles or electromagnetic radiation. In these reactions, rest mass is not conserved, although (as in any other reaction) energy is conserved.
Sources of antimatter
Antiparticles are created everywhere in the universe where high-energy particle collisions take place, such as in the center of our galaxy, but few have been detected that are residual from the Big Bang, as most normal matter is.
Exploding stars can produce it during stellar outbursts, but it is possible more exotic processes can take place in the universe. Dark matter has been theorized to decay into other particles - including antimatter - through unknown principles.
Another potential source is a certain kind of binary star system, where an exotic compact object, like a white dwarf, neutron star or black hole, is locked in gravitational interaction with a regular star. The exotic star siphons away material, which piles up on its surface. In this extreme environment, antimatter could be spontaneously generated in the intense radiation field.
Producing antimatter using particle accelerators is under normal circumstances prohibitively expensive, often because producing antimatter tanks prohibitive amounts of energy. By simply placing solar collectors in the orbit of a sun one can reduce power costs dramatically by harvesting its virtually free energy. Each particle accelerator only produces a trickle of antimatter, so to speak, but since the energy is abundant from a sun one can run many particle accelerators at once to make a fair amount of antimatter.
Antimatter as fuel
In antimatter-matter collisions, the entire rest mass of the particles is converted to energy. The energy per unit mass is about 10 orders of magnitude greater than chemical energy, and about 2 orders of magnitude greater than nuclear energy that can be liberated using chemical reactions or nuclear fission/fusion. Antimatter Reactors based on this principle are employed in many starships and orbital installations as a more efficient alternative to fusion.
When a particle of antimatter meets its normal matter counterpart, the two particles annihilate each other in a powerful blast of gamma rays. This burst of radiation is very specific; the gamma rays from a matter/antimatter annihilation carry exactly 511 thousand electron-volts of energy. Freefloating antimatter in the Universe, although exceedingly rare, can thus be looked for by starships in need of wilderness refueling simply by scanning for 511 keV emissions.
Antimatter as an explosive
Many primarily torpedo-based weapons systems use anti-matter as a potent explosive. The anti-matter is usually suspended in a magnetic containment field and, once the target is reached, combined with an equal amount of regular matter, creating a violent explosion of pure energy.