barred Magellanic spiral
mârpic-e mile-dâr-e Mâželâni
Fr.: spirtale barée magellanique
A transitional class of object between the classic spiral galaxies and true irregular systems. The → Large Magellanic Cloud, the nearest and best studied example of the class, is, contrary to popular opinion, not an irregular galaxy. The LMC and other members of the SBm class have definite structural signatures. They are generally dominated by a pronounced asymmetric bar -- one that is offset from the optical center of the galaxy -- with a nascent spiral arm emanating from one end. As is the case with irregular galaxies, the optical centers of SBm type systems are not particularly special places. Disk systems later than Sc characteristically lack a central stellar concentration in addition to having weak spiral structure; this is true of SBm-type galaxies. SBm galaxies are typically very active in their star formation activity, often containing a large star-forming complex situated at one end of the bar. Beyond these general trends there is a tremendous amount of dispersion in physical properties within the SBm class, particularly in the strength of the spiral structure. At one extreme are the "one-armed" spirals such as NGC 3664 and NGC 4027 which are dominated by single, looping spiral arm. On the other hand NGC 4861 shows little evidence of spiral structure and it is dominated by a large star-forming complex at one end of its bar. The class smoothly leads to the Barred Magellanic irregulars (IBm) which show no indication of spiral structure (Wilcots et al. 1996, AJ 111, 1575).
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.
Magellanic spiral galaxy
kakhešân-e mârpic-e Mâželâni
Fr.: galaxie spirale magellanique
A class of low-mass galaxies with relatively rare features. In particular, these galaxies are characterized by a → stellar bar whose center is displaced from that of the disk and a one-armed spiral. The → Large Magellanic Cloud (LMC) is considered the prototype of this class of objects. However, despite a wealth of data, there is still a good deal of uncertainty concerning the nature of the LMC's bar. The majority of the observed Magellanic spirals in the nearby Universe share the LMC's structure, in particular the evidence of an offset bar and a one-armed spiral structure. A good example of these systems is NGC 3906, which shows evidence of the bar offset from the photometric center of the galaxy by 1.2 kpc (Pardy et al., 2016, ApJ 827, 149).
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.: nébuleuse 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