An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A very large-scale structure made of → galaxy clusters threaded like beads on a chain. Cosmic filaments are chiefly made up of → dark matter but also, to a lesser extent, of → baryonic matter. They are the largest entities in the → Universe and can be up to 1 billion → light-years long. They are separated by great → voids.

→ cosmic; → filament.

1) A long tongue of a relatively cold matter (10,000 K), suspended in the → solar corona (2 million K). Filaments seem dark in the Hα light when they are seen projected on the solar disk; at the limb they look as what they actually are: → prominences.
2) Electricity, Electronics: In electric light bulbs and thermionic valves, a wire of metal of high melting point, which is heated by the passage of an electric current.
3) Cosmology: → cosmic filament.

From Mod.L. filamentum, from L.L. filare "to spin, draw out in a long line," from L. filum "thread," from PIE base *g^whi- "thread, tendon;" cf. Gk. bios "bow;" Skt. jiyā- "bow-string;" Av. jiiā- "bow-string;" Mod.Pers. zeh "string, bow-string" (dialectal Qomi zij "mason's cord"); Arm. jil "string, line;" Lith. gijà "thread;" Russ. žica "thread."

Rešté "thread, line, file," from reštan, ristan "to spin;" Mid.Pers. 'rws- "to turn to," abrešom "silk;" Sogdian rwyšt "spun;" Av. uruuaēs- "to twist, turn;" Proto-Iranian *uris- "to turn, spin."

A nebula, generally ionized, consisting of filament-like structures of gas, such as the Veil Nebula (NGC 6960) or the supernova remnant IC 443.

Filamentary adj. of → filament; → nebula.

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.

A → stream tube with a small cross section so that the variation of velocity over it is negligible.

→ stream; → filament.