barred spiral galaxy
kahkašân-e mârpic-e miledâr
Fr.: galaxie spirale barrée
mârpic-e Cornu (#)
Fr.: spirale de Cornu
A plane curve whose Cartesian coordinates are given in parametric form by the → Fresnel integrals. Cornu's spiral is an auxiliary tool for calculating the Fresnel integrals. It is particularly used for the calculation of the diffraction of light at the straight edge of a flat screen or at a straight slit. It is characterized by the fact that the angle it makes with the abscissa axis is proportional to the square of the distance along the curve from the origin of coordinates. Cornu's spiral comprises two branches, symmetrical with respect to the origin and winding asymptotically on the points (0.5,0.5) and (-0.5,-0.5) respectively. Also known as the → clothoid or Euler's spiral.
Named after the French physicist Alfred Cornu (1841-1902); → spiral.
dwarf spiral galaxy
kahkašân-e mârpic-e kutulé (#)
Fr.: galaxie spirale naine
A galaxy that belongs to the spiral class but is significantly smaller.
extreme mass ratio inspiral (EMRI)
forupicé bâ vâbar-e ostom-e jerm
Fr.: orbite plongeante d'un trou noir binaire, au rapport de masse extrême
A compact stellar remnant (e.g., a → white dwarf, → neutron star, or → black hole) that undergoes → inspiral into a much more massive object (→ supermassive black hole found → galactic centers). EMRIs are potential sources of low-frequency → gravitational waves. Predictions of the EMRI event rates span a wide range, from ~ 10-9 to 10-6 yr-1 per galaxy (Merritt et al. 2011, Physical Review D 84, 044024). See also → resonant relaxation.
flocculent spiral galaxy
kahkešân-e mârpic-e pašmin
Fr.: galaxie spirale floculente
A galaxy that has short segments of patchy spiral structure so that the disk appears like the fleece of a sheep. Examples: NGC 2841 and NGC 5055.
From L. floccus "flock of wool" + -ulent; → spiral galaxy.
Kahkešân, → galaxy; mârpic, → spiral; pašmin "woolly, woollen," from pašm "wool" (Mid.Pers. pašm "wool;" Av. pašna- "eyelash, eyelid;" cp. Skt. páksman- "eyelashes;" Gk. pekos "wool, fleece," pek(t)ein "to comb, pluck;" Lith. pešti "to pluck;" O.N. fax "mane").
grand design spiral galaxy
kahkešân-e mârpic-e farsâz
Fr.: galaxie spirale parfaite
A galaxy with prominent → arms that are clearly attached to the central → bulge or → bar spiraling continuously outward until they reach the edge of the visible disk. Some examples are: → Whirlpool galaxy (M51), M74 (NGC 628), and NGC 2997.
M.E. graunt, from O.Fr. grant, grand, from L. grandis "big, great," also "full-grown;" design, from M.E. designen, from L. designare "mark out, designate, appoint," from → de- "out" + signare "to mark," from signum→ sign; → spiral; → galaxy.
Fr.: orbite plongeante en spirale
The inward spiraling of an orbiting → black hole toward a central → supermassive black hole (SMBH) as it radiates → gravitational wave. As a result, the orbit decays, and the orbital period decreases, leading to the → merging of both black holes as they get close enough. Once merged, the single hole goes through a stage called → ringdown.
Running continuously around a fixed point or center while constantly receding from or approaching it.
From M.Fr. spiral, from M.L. spiralis "winding, coiling," from L. spira "coil," from Gk. speira "coil, twist, wreath."
Mârpic, literally "snake coil," from mâr "snake, serpent," → Serpens, + pic, present stem of picidan "to twist, entwine, coil," ultimately Proto-Iranian *paticā-citanai- "to coil;" cf. Av. paitica "inversely; back" and ci- (caē-, caii-) "to heap up, gather" (Nyberg 1974).
Fr.: bras spiral
Fr.: galaxie spirale
Fr.: structure spirale
The morphology of a galaxy which displays → spiral arms.
strong arm spiral galaxy
kahkešân-e mârpic bâ bâzu-ye setorg
Fr.: galaxie spirale à forts bras
A galaxy with prominent stellar → spiral arms and little star formation between stellar arms, such as M51.
weak arm spiral galaxy
kahkešân-e mârpic bâ bâzu-ye nezâr
Fr.: galaxie spirale à faibles bras