An Etymological Dictionary of Astronomy and Astrophysics
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Any of many long and slender structures visible in → radio continuum images of the inner hundred parsecs of the → Galactic Center. NTFs are typically tens of parsecs long and only a fraction of parsec wide. They may occur in isolation or in bundles, such as those comprising the linear portion of the prominent → radio Arc. Their → non-thermal spectrum and strong → linear polarization indicate → synchrotron radiation. The magnetic fields in the NTFs have been estimated from various means. Early estimates centered on the radio Arc, and focused on a comparison between the → magnetic pressure and the estimated → ram pressure from nearby → molecular cloud interactions, indicated magnetic field strengths as high as 1 mG (Morris and Yusef-Zadeh 1985). More recent observations, however, have pointed to significantly weaker magnetic fields among the population of NTFs. Synchrotron models of the radio spectrum imply equipartition magnetic fields between 50-200 μG. Theoretically, it has been challenging to understand the nature of these filaments that resemble extragalactic → radio jets but are not accompanied with any obvious source of acceleration of charged particles to high energy → relativistic energies. Although a number of detailed models have been considered, there is no consensus as to the origin of the NTFs. These models suggest that molecular and ionized gas clouds, mass-losing stars, → Galactic winds, magnetic activity of the → supermassive black hole at the Galactic center, and → lepton production due to → dark matter annihilation play a role in the processes that lead to the production of the NTFs (Linden et al. 2011, ApJ 741,95, and references therein). In most models, the magnetic field is strong and its global geometry in the central region of the Galaxy is considered to be → poloidal and static. However, some recent models have argued that the magnetic field is local and dynamic.

→ non-thermal; → filament.

The electromagnetic radiation whose characteristics do not depend on the temperature of the emitting source. In contrast to → thermal radiation, it has a different spectrum from that of → blackbody radiation. The three common types of non-thermal radiation in astronomy are: → synchrotron radiation, → bremsstrahlung radiation, and → maser  → stimulated emission.

→ non-thermal; → radiation.

A radio emission with a negative → spectral index. In this type of emission the intensity of the emitted radiation increases with wavelength.

→ non-thermal; → spectrum.

Not equal to zero.

→ non-; → zero.

A → polynomial that at least has one non-zero → coefficient. See also → zero polynomial.

→ non-zero; → polynomial.

The absorption of a photon and its re-emission at a different frequency (in the observer's frame of reference) by scattering atoms.

→ non-; → coherent scattering.

A plasma in which the → mean free path of the charged particles between two collisions is much larger than the size of the system containing the plasma.

→ non-; → collisional; → plasma.

An equation that is independent of the units of measurement as it only involves nondimensional numbers, parameters, and variables.

→ non-; → dimensional; → equation.

Describing something that is partially or totally occupied.

→ non; → empty.

A set containing at least → one → element.

→ nonempty; → set.

Math.: The fact that no → solution exists for a given → problem. In mathematics, nonexistence usually is a matter of impossibility.

→ non-; → existence.

Not → fuzzy. → nonfuzzy set.

→ non-; → fuzzy.

A set that obeys the rules of → classical logic, a → crisp set, as contrasted with a → fuzzy set.

→ nonfuzzy; → set.

A mechanical system with constraints on their velocity that are not derivable from position constraints. Nonholonomic systems arise, for instance, in mechanical systems that have rolling contact (for example, the rolling of wheels without slipping) or certain kinds of sliding contact (such as the sliding of skates). They are a remarkable generalization of classical Lagrangian and Hamiltonian systems in which one allows position constraints only.

→ non-; → holonomic; → system.

Not homogeneous. → nonhomogeneous linear differential equation.

→ non-; → homogeneous.

A → linear differential equation if Q(x)≠ 0 on interval I.

→ nonhomogeneous; → linear; → differential; → equation.

The quality of an atom that has neither lost nor gained any electrons.

→ non-; → ionized.

Not a linear function of the relevant variables.
Containing a variable with an exponent other than one; opposite of → linear.

→ non-; → linear.

An electronic device whose output is not directly proportional to its input. For example, in a → diode the current is a nonlinear function of the voltage; its voltage-current characteristics do not obey → Ohm's law.

→ nonlinear; → device.

Same as → chaos.

→ nonlinear; → dynamics.