An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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ultra-
  اولتر-   
ultar- (#)

Fr.: ultra-   

A prefix occurring originally in loanwords from L., with the basic meaning "on the far side of, beyond, extremely."

From L. ultra- from ultra (adverb and preposition) "beyond, on the further side," from *ulter, from uls "beyond;" + *-ter suffix of comparative adj.; PIE base *al- "besides, other, beyond."

Ultar-, from Mid.Pers. ul "up, upward," ulêh "upward, above" (Av. ərəδuua- "upright, risen; cf. Skt. ūrdhvá- "high, above, elevated; Gr. orthos "set upright, straight;" L. arduus "high, steep;" → ortho-) + -tar suffix forming comparative adjectives (Mid.Pers. -tar; Av. -tara- (masculine); PIE base *-tero).

ultra-diffuse galaxy (UDG)
  کهکشان ِ اولتر-پخشیده   
kahkešân-e ultar-paxšide

Fr.: galaxie ultra-diffuse   

A galaxy of low stellar density, defined to have low central → surface brightness (> 24 mag arcsec-2) and an → effective radius (Re) of over 1.5 kpc. The question of whether UDGs represent a separate class of galaxies is still under debate. Currently, known UDGs that have been discovered in clusters, in groups, and in the field can have Re as large as 5 kpc which is comparable to that of giant Milky Way like galaxies. This fact has been used to suggest that UDGs are "failed" giants. As Re captures (at most) the central parts of giant galaxies, whether this radius can be used to fairly compare the sizes of UDGs to the more massive galaxies is questionable (see, e.g., Chamba et al., 2020, A&A 633, L3).

Term proposed by van Dokkum et al. (2015), arXiv: 1410.8141v2; → ultra-; → diffuse; → galaxy.

ultra-high-energy cosmic ray (UHECR)
  پرتوهای ِ کیهانی ِ اولتر-مه-کاروژ   
partowhâ-ye keyhâni-ye ultar-meh-kâruž

Fr.: rayons cosmiques de très haute énergie   

A particle belonging to the most energetic population of → cosmic rays with an energy above ~ 1020 → electron-volts. The UHECRs constitute a real challenge for theoretical models, because their acceleration requires extreme conditions hardly fulfilled by known astrophysical objects. See also → UHECR puzzle, → Greisen-Zatsepin-Kuzmin cutoff.

ultra- + → high-energy cosmic ray.

ultra-high-energy neutrino
  نوترینو‌ی ِ اولتر-مه‌کاروژ   
notrino-ye ultar-meh-kâruž

Fr.: neutrino ultra haute énergie   

A neutrino particle accelerated to energies above 1018 → electron-volts. They are produced by the interaction of → ultra-high-energy cosmic ray (UHECR)s with the → cosmic microwave background radiation. Also called → cosmogenic neutrinos. See also → Greisen-Zatsepin-Kuzmin limit.

ultra-; → high; → energy; → neutrino.

ultracompact
  اولتر-همپک   
ultar-hampak

Fr.: ultracompact   

Extremely compact with respect to a comparison value. → ultracompact H II region, → ultracompact dwarf galaxy.

ultra-; → compact.

ultracompact dwarf galaxy (UCD)
  کهکشان ِ کوتوله‌ی ِ اولتر-همپک   
kahkešân-e kutule-ye ultar-hampak

Fr.: galaxie naine ultracompacte   

A type of very bright compact → stellar system (-14 ≤ MV≥ -12) that is intermediate between → globular clusters (GCs) and → compact elliptical galaxies (cEs). With masses of M > 2 × 106 Msun and radii > 10 → parsecs (pc), UCDs are among the densest stellar systems in the Universe. Nevertheless, the nature and origin of these objects is still widely debated. Early interpretations suggested that UCDs could be the most massive GCs or possibly the → tidally stripped remnants of → dwarf galaxies. However, there is evidence that both formation mechanisms could contribute to the UCD population. → Supermassive black holes (SMBHs) have been confirmed in most UCDs with masses M > 107 Msun. The most massive UCD discovered to date, M59-UCD3 (M* ~ 2 × 108 Msun, radius ~ 25 pc), hosts a SMBH (Ahn et al., 2018, arxiv/1804.02399, and references therein).

ultracompact; → dwarf; → galaxy.

ultracompact H II region
  ناحیه‌ی ِ H IIی ِ اولتر-همپک   
nâhiye-ye H II-ye ultar hampak

Fr.: région H II ultracompacte   

A very young → H II region fully embedded in its natal molecular cloud. Ultracompact H II regions are distinguished from classical H II regions by their small sizes (diameter ≥ 0.1 pc), high densities (Ne ≥ 105 cm-3), and high emission measures (EM ≥ 107 pc cm-6). Their typical ionized gas content is about 10-2  → solar masses, in contrast to classical H II regions with a mass of about 105 solar masses. Due to very important extinction, ultracompact H II regions are not accessible to visible wavelengths.

ultra-; → compact; → H II region.

ultracool dwarf
  کوتوله‌ی ِ اولترسرد   
kutule-ye ultarsard

Fr.: naine ultrafroide   

A star-like objects with an → effective temperature of less than 2,700 K. Ultracool dwarfs constitute a heterogeneous group including stars of extremely low mass as well as → brown dwarfs, and represent about 15% of the population of astronomical objects near the Sun.

ultra-; → cool; → dwarf.

ultraluminous
  اولتر-تابان   
ultar-tâbân

Fr.: ultralumineux   

The quality of an object whose → luminosity exceeds a certain value.

ultra-; → luminous.

ultraluminous infrared galaxy (ULIRG)
  کهکشانِ فروسرخ ِ اولتر-تابان   
kahkešân-e forusorx-e ultar-tâbân

Fr.: galaxie ultralumineuse en infrarouge   

A galaxy that emits more than 90% of its energy in the infrared (8-1000 µm) and whose infrared luminosity exceeds 1012 solar luminosities. → luminous infrared galaxy (LIRG). Quasars can also have such high or even higher bolometric luminosities. However LIRGs and ULIRGs emit the bulk of their energy in the infrared. Most of ULIRGs are found in merging and interacting galaxy systems. It is thought that their luminosity results from galactic collisions, which increase the rate of star formation.

ultraluminous; → infrared; → galaxy.

ultraluminous X-ray source (ULX)
  خن ِ پرتو ِ ایکس ِ اولتر-تابان   
xan-e partow-e iks-e ultar-tâbân

Fr.: source ultralumineuse en rayons X   

An X-ray source that is not in the nucleus of a galaxy, and is more luminous than 1039 ergs s-1, brighter than the → Eddington luminosity of a 10 → solar mass → black hole. In general, there is about one ULX per galaxy in galaxies which host ULXs. The Milky Way contains no such objects. ULXs are thought to be powered by → accretion onto a → compact object. Possible explanations include accretion onto → neutron stars with strong → magnetic fields, onto → stellar black holes (of up to 20 → solar masses) at or in excess of the classical Eddington limit, or onto → intermediate-mass black holes (103-105 solar masses). NGC 1313X-1, NGC 5408X-1, and NGC 6946X-1 are three ULXs with X-ray luminosities up to ~ 1040 erg s-1 (Ciro Pinto et al., 2016, Nature 533, N) 7601).

ultraluminous; → X-ray source.

ultrarelativistic
  اولتر-بازانیگی‌مند   
ultar-bazânigimand

Fr.: ultrarelativiste   

Describing a system or situation for which the → Lorentz factor, γ, is much larger than 1. See also → subrelativistic.

ultra- + → relativistic

ultrarelativistic gas
  گاز ِ اولتر-بازانیگی‌مند   
gâz-e ultar-bazânigimand

Fr.: gaz ultrarelativiste   

A gas composed of ultrarelativistic particles.

ultrarelativistic; → gas.

ultrashort-period Cepheid
  کفیءوسی ِ اولتر-کوتاه-دوره   
Kefeid-e ultar-kutâh-dowré

Fr.: céphéide à très courte période   

A → Cepheid star of → spectral type A-F with regular pulsation period of 1-3 hours and with small variations in amplitude. This group is also known as δ Scuti stars.

ultra-; → short; → period; → Cepheid.

ultrasonics
  اولتر-صداییک، اولتر-سداییک   
ultar-sedâyik

Fr.: physique des ultra-sons   

The branch of physics dealing with elastic waves of frequencies above 20 kHz to 1010 kHz propagated in solids, liquids, and gases.

ultra-; sonic from L. sonussound + → -ics.

ultrasound
  اولتر-صدا، اولتر-سدا   
ultar-sedâ

Fr.: ultra-son   

Sound with a frequency lying above the audition frequency range, usually taken to be about 20 kHz. → sound wave.

ultra- + → sound.

ultraviolet (UV)
  فرابنفش، اولتر-بنفش   
farâ-banafš, ultar-banafš

Fr.: ultraviolet   

The part of the electromagnetic radiation beyond the violet end of the visible spectrum with wavelengths approximately in the range 50 Å to 4,000 Å. → extreme ultraviolet; → far ultraviolet.

ultra-; → violet.

ultraviolet astronomy
  اخترشناسی ِ فرابنفش، ~ اولتر-بنفش   
axtaršenâsi-ye farâ-banafš, ~ ultar-banafš

Fr.: astronomie ultraviolette   

The study of astronomical objects in the ultraviolet portions of the electromagnetic spectrum, in the waveband 3000 Å to about 10 Å. At these wavelengths, the atmosphere prevents ultraviolet radiation from reaching the Earth surface. Therefore ground-based observatories cannot observe in the ultraviolet. Only with the advent of space-based telescopes has this area of astronomy become available for research.

ultraviolet; → astronomy.

ultraviolet catastrophe
  نگونزار ِ فرابنفش   
negunzâr-e farâbanafš

Fr.: catastrophe ultraviolette   

A → paradox encountered in the classical theory of → thermal radiation (→ Rayleigh-Jeans law), whereby a → blackbody should radiate an infinite amount of energy at infinitely short wavelengths, in contradiction with what is observed. The problem was solved by Max Planck in 1900, who suggested that, rather than being continuous, the energy comes in discrete parcels called → quanta. The avoidance of the ultraviolet catastrophe was one of the first great achievements of → quantum mechanics.

This problem was first raised by Lord Rayleigh (1842-1919), whereas the term ultraviolet catastrophe was first used by Paul Ehrenfest (1880-1933); → ultraviolet; → catastrophe.

ultraviolet excess
  فزونی ِ فرابنفش، فرهبود ِ اولتر-بنفش   
fozuni-ye farâbanafš, ferehbud-e ultar-banafš

Fr.: excès ultraviolet   

Ultraviolet emission from an object in excess of that expected for a reference. For example, → subdwarf stars show ultraviolet excess with respect to that expected from a star with → solar metallicity at a given → effective temperature. In this case, UV excess results from smaller → line blanketing in → population II stars.

ultraviolet; → excess.

<< < -es -it -sc 201 951 abe abs abs aca acc acc aco act ada adh ado aer aft air Alf alg alk alp Alt alt amb ana And ang ani ann ant ant ant apo app app Apu arc arg Arn art ass ast ast ast atm ato att aur aut avo azi bac bal bar bar bat Bea Bel bet bia big bin bio Bir bla bla blo Blu bol Boo bou box bre Bri bro bur cal cal Can cap car Car cat cau cel cen cen cha Cha cha che Chi chr cir cir civ cla clo clo CMB coa coe coh col col col com com com com com com com com Com con con con con con con con con con con con con coo cor cor cor Cos cos cos cou cou cra cri cro cry cul cur cyc D l dar dat day dea dec dec dec def def deg Del Den dep der det deu dew dic dif dif dil dip dir dis dis dis dis dis diu dog Dop dou Dra Dsc dus dwa dyn Dys Ear ecc eco edg egg Ein Ela ele ele ele ele ell eme emp enc eng ent epi equ equ equ eru eth Eur eve exa exc exe exi exo exp ext ext ext fab fai Fan fea fem fer fie fil fir fir fla fli flu foc for for for fra fre fre fri fun fuz gal gal gal Gam gau Gau gen geo geo geo geo Gib glo gov gra gra gra gra gre gro Gui H-a hal Ham har Hay hea hei hel Hel her het hie hig hoa hom hor hot Hub Hug hur hyd hyd hyl hyp ice ide ima ima imp imp inc inc ind ine inf inf inf ing inn ins ins int int int int int int int int inv inv ion iro Isl iso iso Jab jet Jov Jup Kar Kep kil Kip Kra Lag Lam Lan Lar las law lea Leg Leo lev lig lim lin lin lin lit loc loc log Lor low lum lun lun Lym Mac mag mag mag mag mag mai Mal map mas mas mat Mau mea mea med Men mer Mes Met met mic mic Mie mil min Mir mix mod mol mom Moo mor mov mul mur n-b nan nat nea neg Ner neu new New NGC noc nom non non nor nor nuc nuc nul nut obj obl obs occ oct off old one ope opp opt opt orb ord org Ori osc oth ove Owl P-s Pal par par par par Pas pat pec pen per per per per per Pha pha pho pho pho phy pie pix Pla pla pla pla Pli Poi pol pol pol pol por pos pos pow pre pre pre pre pri pri pri pro pro pro pro pro pro pro pub pul pyc qua qua qua qua qui rad rad rad rad rad rad rai ran rar Ray rea Rea rec rec red red ref ref reg rel rel rel ren res res res res ret rev Ric rig rin roc roo rot rot rur S5- Sal sat sca sca Sch sci Scu sec sec sed sel sel sem seq set sha she sho sid sie sil sim sin sit sky slo sno sod sol sol sol sol son sou spa spa spe spe spe spe sph spi spo squ sta sta sta sta ste ste ste Sti sto str str sub sub sub sul sup sup sup sup sur sur syl syn sys tal Tay tel ten ter tex the the the the Tho thr tid tim Tit too Tor tra tra Tra tra Tra tri Tri tru tub tur two Typ ult ult unc uni uni uni upl ura uti val var vec vel ver Ver vie vir vis vis vol W-R war wav wav wea Wei wha wid win WN3 Wol wri xen yok zen zij > >>