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B-mode polarization qotbeš-e tarz-e B Fr.: polarisation en mode B A → polarization component in the → cosmic microwave background radiation that depends only on → curl, is independent of → gradient, and has → handedness that distinguishes left from right. The B-mode is due to only → vector perturbations or → tensor perturbations. It has two types, the first type, which constitutes the majority of the B-mode polarization, results from → lensing by galaxies that twist the → E-mode polarized light on its journey from the other side of the → observable Universe. The second type can be produced only by → gravitational waves, not by density perturbations. This type of B-mode is incredibly faint, producing temperature variations of about 0.4 microK and accounting for just one part in 10 million in the CMB temperature distribution. It is expected to be generated during cosmic → inflation shortly after the → Big Bang. The → BICEP2 team announced in March 2014 that they had detected the second type of B-modes, consistent with inflation and gravitational waves in the → early Universe. The detected degree scale B-mode polarization has a tensor-to-scalar ratio, r = 0.2 (+0.07, -0.05), which is a measure of the amplitude of the primordial gravitational waves. B, indicating magnetic-field like; → mode; → polarization. |
background radiation tâbeš-e paszaminé, ~ zaminé Fr.: rayonnement du fond The isotropic residual microwave radiation in space left from the primordial → Big Bang. Same as → cosmic microwave background (CMB) radiation. → background; → radiation. |
barrel distortion cowlegi-ye celiki (#) Fr.: distortion en barillet A defect in an optical system in which magnification decreases with distance from the optical axis, whereby the image of a square appears barrel-shaped. Opposite of → pincushion distortion. Barrel, M.E. barel, from O.Fr. baril; → distortion. Cowlegi, → distortion; celiki, relating to celik "barrel". |
baryon acoustic oscillation (BAO) naveš-e sedâyik-e bâryoni Fr.: oscillation acoustique baryonique In cosmology, one of a series of peaks and troughs that are present in the power spectrum of matter fluctuations after the → recombination era, and on large scales. At the time of the Big Bang, and for about 380,000 years afterwards, Universe was ionized and photons and baryons were tightly coupled. Acoustic oscillations arose from perturbations in the primordial plasma due to the competition between gravitational attraction and gas+photons pressure. After the epoch of recombination, these oscillations froze and imprinted their signatures in both the → CMB and matter distribution. In the case of the photons, the acoustic mode history is manifested as the high-contrast Doppler peaks in the temperature anisotropies. As for baryons, they were in a similar state, and when mixed with the non-oscillating → cold dark matter perturbations, they left a small residual imprint in the clustering of matter on very large scales, ~100 h^{-1}Mpc (h being the → Hubble constant in units of 100 km s^{-1} Mpc^{-1}). The phenomenon of BAOs, recently discovered using the Sloan Digital Sky Survey data, is a confirmation of the current model of cosmology. Like → Type Ia supernovae, BAOs provide a → standard candle for determining cosmic distances. The measurement of BAOs is therefore a powerful new technique for probing how → dark energy has affected the expansion of the Universe (see, e.g., Eisenstein 2005, New Astronomy Reviews 49, 360; Percival et al. 2010, MNRAS 401, 2148). → baryon; → acoustic; → oscillation. |
Bayer designation nâmgozini-ye bayer Fr.: designation de Bayer A stellar designation system in which a specific star is identified by a Greek letter, followed by the genitive form of its hosting → constellation's Latin name. For example, Alpha Eridani, Delta Cephei, Lambda Bootis. The Greek alphabet has only 24 letters. In case a single constellation contained a larger number of stars, Bayer amended with Latin letters: upper case A, followed by lower case b through z (omitting j and v), for a total of another 24 letters. Bayer did not go beyond z, but later astronomers added more designations using both upper and lower case Latin letters, the upper case letters following the lower case ones in general. Examples include, for Vela: a Vel (Velorum), z Vel, A Vel, Q Vel; for Scorpius: d Sco (Scorpii), A Sco; for Leo: b Leo (Leonis), o Leo, A Leo, → c Orionis. Compare with the → Flamsteed designation. First introduced by Johann Bayer (1572-1625) in his atlas Uranometria, published in 1603 at Augsburg, Germany; → designation. |
Bellatrix (γ Orionis) Bellatriks, Merzam Fr.: Bellatrix A bright, blue → giant star ( → spectral type B2 III), one of the main stars of the constellation → Orion. With a visual magnitude of 1.64, it is about 1000 times more luminous than the Sun, and lies at a distance of 243 → light-years. From L. bellatrix "a female warrior," fem. of bellator, from bellum "war." Merzam, Ar. name of the star; its other name is Nâjed. |
Belt of Orion kamarband-e Šekârgar, ~ Oryon Fr.: Baudrier d'Orion → Orion's Belt. |
Bernoulli equation hamugeš-e Bernoulli Fr.: équation de Bernoulli The equation expressing → Bernoulli's theorem: P + (1/2)ρV^{2} + ρgz = constant, where P is the fluid → pressure, V is → velocity, ρ is → density, g is the acceleration due to → gravity, and z is the vertical reference → level. The theree terms are called → static pressure, → dynamic pressure, and → hydrostatic pressure, respectively. The Bernoulli equation states that the total pressure along a → streamline is → constant. → Bernoulli's theorem; → equation. |
Bessel equation hamugeš-e Besel Fr.: équation de Bessel A linear second-order differential equation, the solutions to which are called Bessel functions. Hamugeš, → equation. |
Betelgeuse (α Orionis) Ebtoljowzâ (#) Fr.: Bételgeuse The → red supergiant that is the second brightest star in the constellation → Orion. Betelgeuse is one of the biggest stars known with a size of almost 1,000 times larger than the Sun, corresponding to an angular diameter of 43.76 ± 0.12 milli-arcseconds (Perrin et al. 2004, A&A 418, 675). It is a → semiregular variable whose → apparent visual magnitude varies between 0.2 and 1.2 shining very rarely more brightly than its neighbor → Rigel. The energy released by Betelgeuse is estimated to be only 13% in the form of visible light, with most of its radiation being at → infrared wavelengths. The distance of Betelgeuse is 643±146 → light-years (Harper et al. 2008, AJ 135, 1430), while its luminosity is about 140,000 times that of the Sun (→ solar luminosity). Its → spectral type is M2 Iab, its → surface temperature about 3,600 K, and its → initial mass 10 to 20 → solar masses (M_{sun}). Neilson & Lester (2011, arXiv:1109.4562) recently proposed a mass of 11.6 (+5.0, -3.9) M_{sun} for Betelgeuse, while Dolan et al. (2008, BAPS 53, APR.S8.6) obtained about 21 M_{sun}. Its → rotation period is estimated to be about 17 years (Uittenbroek et al. 1998, AJ 116, 2501). Recent observations with the → Very Large Telescope resolve not only the apparent surface of Betelgeuse, but also reveal a large and previously unknown plume of gas extending into space from the surface of the star (Kervella et al. 2009, A&A 504, 115). The plume extends to at least six times the diameter of the star, corresponding to the distance between the Sun and Neptune. This detection suggests that the whole outer shell of Betelgeuse is not shedding matter evenly in all directions. More recently, an image of the surface of the star was obtained using long → baseline → interferometry at infrared wavelengths (Haubois et al. 2009, A&A 508, 923). It shows the presence of an irregular flux distribution possibly caused by enormous → convective cells. A very large dusty envelope has also been observed at larger distances from the star (Kervella et al. 2011, A&A 531, A117). Betelgeuse, from Ar. Ibt al-Jauza' ( Ebtoljowzâ, from Ar. Ibt al-Jauza'. |
biased galaxy formation diseš-e varakdâr-e kahkašânhâ Fr.: formation biaisée de galaxies The theory that bright galaxies form preferentially from anomalously overdense perturbations in the → early Universe. |
bifurcation dogaleš Fr.: bifurcation 1) A branching or division into two parts; a splitting apart. Verbal noun of → bifurcate. |
bifurcation point noqte-ye dogaleš Fr.: point de bifurcation The point or moment in the evolution of a → dynamical system that occurs if a parameter passes through a critical point. At this point the system branches into any number of qualitatively new types of behavior. → bifurcation; → point. |
bifurcation theory negare-ye dogaleš Fr.: théorie de bifurcation 1) A theory which studies how, in certain nonlinear systems, there may be paths
and shifts in behavior dependent on small changes in circumstances or the current position
of the system. → bifurcation; → theory. |
bijection došâneš Fr.: bijection A → mapping f from a → set A onto a set B which is both an → injection and a → surjection. More explicitly, for every element b of B there is a unique element a of A for which f(a) = b. Also known as → bijective mapping. From bi- + → injection. |
bimodal star formation diseš-e domod-e setâregân Fr.: formation bimodale d'étoile A concept of → star formation in which → high-mass stars and → low-mass stars form in different physical conditions involving different → molecular clouds. Following the pioneering suggestion of Herbig (1962), successive investigations have generally supported the idea that star formation proceeds bimodally with respect to stellar mass. The star formation rate appears to differ both spatially and temporally for low mass and → massive stars. This is of considerable importance for galactic evolution, since the low-mass stars lock up mass and are long-lived, low luminosity survivors to the present epoch, whereas massive stars are short-lived, recycle and enrich interstellar gas, and leave dark remnants while producing a high luminosity per unit of mass (Silk, J., 1988, in Galactic and Extragalactic Star Formation, p. 503, eds. R. E. Pudritz and M. Fich). |
binary operation âpâreš-e dorin Fr.: opération binaire A mathematical operation that combines two numbers, quantities, sets, etc.,
to give a third. For example, multiplication of two numbers is a binary operation. |
binomial distribution vâbâžeš-e donâmin Fr.: distribution binomiale A probability distribution for independent events for which there are only two possible outcomes i.e., success and failure. The probability of x successes in n trials is: P(x) = [n!/x!(n - x)!] p^{x}.q^{n - x}, where p is the probability of success and q = 1 - p the probability of failure on each trial. These probabilities are given in terms of the → binomial theorem expansion of (p + q)^{n}. → binomial; → distribution. |
binomial expansion sopâneš-e donâmin Fr.: expansion binomiale A rule for the expansion of an expression of the form (x + y)^{n}. The variables x and y can be any → real numbers and n is an → integer. The general formula is known as the → binomial theorem. |
birth binary population (BBP) porineš-e dorinhâ hengâm-e zâdmân Fr.: population binaire à la naissance In star formation models, the population of binary components formed via random pairing of stars distributed according to the → canonical IMF. → birth; → binary; → population. |
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