An Etymological Dictionary of Astronomy and Astrophysics
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A → thermodynamic process in which no → heat is supplied to or rejected from a system. → polytropic process.

→ adiabatic, → process.

A class of → nuclear fusion reactions by which stars convert → helium into → heavy elements. Once carbon has been created, through → triple alpha process, in a star's interior, it can then continue to fuse with further → alpha particles to produce progressively heavier elements called → alpha particles. The first stage produces oxygen, followed by neon, magnesium, silicon, sulfur, argon, calcium, titanium, chromium and iron. This is known as the → alpha ladder, with energy released as a photon at each stage.

→ alpha;→ process.

A mechanism for the extraction of energy from a rotating → Kerr black hole. It relies on the assumption that the material → accreted by a → black hole would probably be → magnetized and increasingly so as the material gets closer to the → event horizon. Since all black holes of current astrophysical interest are probably accreting from magnetized disks, this has led to suggestions that the Blandford-Znajek process plays a vital role in → active galactic nuclei (AGN) and other accreting black hole systems. The power, P, generated is given by: P = (4π/μ₀) B²R_S²c, where B is the → magnetic field of the → accretion disk, and R_S is the → Schwarzschild radius of the black hole. As an example, for a 10⁸ solar mass black hole with a 1 T magnetic field, the power generated is approximately 2.7 × 10³⁸ W. In perspective, the annual energy consumption of the world is estimated around 5 × 10²⁰ J. The example case presented produces more energy in a single second than the entire globe consumes in a year. While this is a bold claim to make, it is only an example case where not all the energy produced is extractable as useable energy. However, at that point, even a system which is less that < 10-15 % efficient would be sufficient to supply enough energy to power the world for a full year. Of course, the system itself is limited in its lifetime due to the extraction of energy by slowing down the rotation of the black hole. Hence, the system can only exist as long as the black hole has angular momentum, continuing to rotate. At some point, the rotation will cease and the energy source will be unusable (D. Nagasawa, PH240, Stanford University, Fall 2011).

Blandford, R. D., & Znajek, R. L., 1977, MNRAS 179, 433; → process.

The production of an → electron-positron pair in the → collision of two → gamma ray → photons (γγ → e⁺e^-). It is the → inverse process of → Dirac annihilation (e⁺e^-→ γγ). The Breit-Wheeler process is the simplest way by which pure → light can be potentially transformed into → matter. However, as of 2014, this process has never been observed in practice because of the difficulty in preparing colliding → gamma ray beams.

Breit, G. & Wheeler, J. A. 1934, Collision of two light quanta. Phys. Rev. 46, 1087; → process.

The primary component of a → computer that processes instructions. It runs the → operating system and → applications, constantly receiving input from the user or active → software programs. The CPU has two typical components: 1) Control Unit, which extracts instructions from memory and decodes and executes them. 2) Arithmetic Logic Unit (ALU), which handles arithmetic and logical operations.

→ central; → processing; → unit.

The process of → radiative cooling in which the → temperature of an astrophysical system decreases due to the radiation of a major → emission line. For example, → molecular → emission at → millimeter wavelengths and → submillimeter wavelengths results in decreasing the temperature in molecular clouds. At temperatures less than 300 K, the main → coolant is the → carbon monoxide (CO) molecule which contains most of the carbon. Similarly, the → [C II] line is a major coolant in → photodissociation regions. See also → line cooling, → cooling time.

→ cooling; → process.

Any sequence of changes in a → thermodynamic system that returns the system into its → initial  → state.

→ cyclic; → process.

Systematic operations on data, such as handling, merging, sorting, and computing.

→ data; → processing.

A machine for handling data in → data processing.

→ data; → processor.

A nuclear or molecular process in which some of the energy of the incoming particle is absorbed by, or transferred to, the other particle.

→ endo- + -ergic, a combining form with the meanings "activated by, sensitive to, releasing, resembling the effect produced by the substance or phenomenon specified by the initial element," from → erg, → energy + → -ic; → process.

Farâravand, → process; kâružgir, from kâruž, → energy, + gir present stem of gereftan "to take, seize, catch" (Mid.Pers. griftan, Av./O.Pers. grab- "to take, seize," cf. Skt. grah-, grabh- "to seize, take," graha "seizing, holding, perceiving," M.L.G. grabben "to grab," from P.Gmc. *grab, E. grab "to take or grasp suddenly;" PIE base *ghrebh- "to seize").

Process during which heat is absorbed by the system from outside.

→ endo- + -therm, from Gk. therme "heat," from PIE *ghwerm-/*ghworm- "warm;" cf. Pers. garm "warm," L. fornax "an oven," O.E. wearm "warm" + → -ic.

From garmâ "heat, warmth" (Mid.Pers. garm, O.Pers./Av. garəma- "hot, warm," cf. Skt. gharmah "heat," Gk. thermos "warm," L. formus "warm," P.Gmc. *warmaz, O.E. wearm, O.H.G., Ger. warm, PIE *ghworm-/*ghwerm-, as above) + gir present tense stem of gereftan "to take, seize, catch" (Mid.Pers. griftan, Av./O.Pers. grab- "to take, seize," cf. Skt. grah-, grabh- "to seize, take," graha "seizing, holding, perceiving," M.L.G. grabben "to grab," from P.Gmc. *grab, E. grab "to take or grasp suddenly;" PIE base *ghrebh- "to seize").

The succession of physical events that results in the breaking of a → molecular cloud into several → fragments.

→ fragmentation; → process.

The use of techniques to produce, extract, identify, and display images for evaluation, interpretation, and further interaction with the data.

→ image; → processing.

A physical process in which the combined → entropy of the → system and the → environment increases. During an irreversible process the system is not in equilibrium at all instances of time. Most of the processes in nature are irreversible. → reversible process.

→ irreversible; → process.

A → thermodynamic process for which there is no → heat transfer with the surroundings, and no change in → entropy.

→ isentropic; → process.

A process taking place at constant pressure. → polytropic process.

Isobaric, adj. of → isobar; → process.

A process in which the volume remains unchanged.

From → iso- + chor-, from Gk. chora "place, land" + → ic.

Farâravand, → process; izogonj, from izo→ iso- + gonj "volume," gonjdan "to be contained; to hold exactly; to be filled;" Mid.Pers. winj- "to be contained;" Proto-Iranian *uiac-/*uic-; cf. Skt. vyac- "to contain, encompass," vyás- "extent, content, extension;" L. uincire "to bind."

A → thermodynamic process that takes place at → constant  → temperature. For the temperature of a system to remain strictly constant, the changes in other coordinates (pressure and volume) must be carried out slowly, and → heat must enter or leave the system to maintain a constant temperature. → polytropic process. Astrophysical examples include the → collapse of a → protostar down the → Hayashi track, and the collapse of a star at the end of its life to become a → white dwarf.

→ isothermal; → process.

The process of collision between galaxies which leads to a single galaxy.

→ merger; → process.

Controlling unit of a microcomputer; laid out on a tiny silicon chip and containing the logical elements for handling data, performing calculations, carrying out stored instructions, etc.

→ micro-; → processor.