An Etymological Dictionary of Astronomy and Astrophysics
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A galaxy belonging to a comparatively rare class of galaxies possessing very small radii and high central → surface brightnesses. The prototype is the → Local Group  → dwarf galaxy M32. At the low mass end of the → early-type galaxy population, the well-known → mass-size relation splits into diffuse and compact branches. The compact branch is composed of compact elliptical galaxies (cEs) and may even extend to the regime of → ultracompact dwarfs. Compact ellipticals have → effective radii (R_e) generally less than 0.6 kpc, while their diffuse counterparts, the → dwarf elliptical galaxies (dEs) or → dwarf spheroidals (dSphs), have R_e ~ 0.6-3 kpc at similar mass. One formation scenario for cEs proposes that they are low-mass classical → elliptical galaxies, in accordance with the fact that they follow the same trend on the fundamental plane as the giant ellipticals. This implies formation through hierarchical mergers, as in "normal" ellipticals. Most cEs are notably more → metal-rich than dEs and are outliers from the → mass-metallicity relation of massive early type galaxies and low-mass galaxies in the Local Group. An alternative formation scenario addresses the problem of high metallicity by proposing that cEs are the remnants of larger, more massive galaxies. In this scenario, their disks are stripped by strong tidal interactions (→ tidal stripping) with an even more massive host galaxy, leaving only the compact, metal-rich bulges (Du et al., 2018, arxiv/1811.06778 and references therein).

→ compact; → elliptical; → galaxy.

An → elliptical galaxy that displays a → surface brightness profile with a distinct break from a steep outer slope to a shallower inner → cusp. Core profiles mainly occur in very luminous elliptical galaxies and are considered the result of dissipation-less → mergers of two galaxies that have central → supermassive black holes (S. P. Rusli et al., 2013, AJ 146, 160).

→ core; → elliptical; → galaxy.

A galaxy that is much smaller than other members of the elliptical class; it is designated as dE. A subtype of dwarf ellipticals is called a → dwarf spheroidal galaxy (dSph). The basic characteristics of the class are low surface brightness and smooth light distribution. They range in luminosity from that of the faintest dSph galaies M_V ~ -9 to about -17. In the → Local Group there are 19 known dEs. They are very common in → galaxy clusters.

→ dwarf; → elliptical; → galaxy.

Relating to or having the form of an → ellipse. Same as → elliptical.

From Gk. elleiptikos "pertaining to an ellipse," from elleipein "to fall short, leave out," from en- "in" + leipein "to leave," + → -ic.

Beyzigun, from beyzi, → ellipse, + -gun, from gun "resembling; manner, fashion; color" (Mid.Pers. gônak "kind, species;" Av. gaona- "color").

That part of → annual aberration proportional to the → eccentricity of the Earth's orbit.

→ elliptic; → aberration.

Pertaining to or having the shape of a geometric ellipse.

→ elliptic; → -al.

A galaxy whose structure is smooth without spiral arms and ellipsoidal in shape. Ellipticals are redder than spirals of similar mass. Giant ellipticals contain over 10¹² solar masses, whereas dwarf ellipticals have masses as low as 10⁷ solar masses.

→ elliptical; → galaxy.

The → polarization of an → electromagnetic radiation in which the electric vector at any point in the path of the beam describes an ellipse in a plane perpendicular to the propagation direction. Elliptical polarization results from the combination of two perpendicular → linearly polarized waves whose → phase difference is other than 0, 90, or 180°. The form of the ellipse is determined by the amplitudes of the component waves and the phase difference. → Linear polarization and → circular polarization can be considered as limiting cases of elliptical polarization.

→ elliptical; → polarization.

Light exhibiting → elliptical polarization.

→ elliptic; → polarized; → light.

The degree of divergence of an ellipse from a circle.

From elliptic-, from elliptical + → -ity.

Beyzigi, from beyzi, → ellipse, + -igi, → -ity.

An → elliptical galaxy whose → surface brightness can be approximated by a single → power law at small radii (r ≤ 10-20''). More modern interpretations have emphasized that these profiles can be better understood as the inward continuation of the galaxy's overall → Sersic profile, usually modified by an additional, nuclear-scale stellar component (S. P. Rusli et al., 2013, AJ 146, 160).

→ power; → law; → galaxy.

A satellite galaxy of the Milky Way discovered only in 1994 since most of it is obscured by the Galactic disc. At only 50,000 light years distant from our Galaxy's core, it is travelling in a polar orbit around the Galaxy. Our Galaxy is slowly devouring it, as evidenced by a filament which stretches around the Milky Way's core like a gossamer loop. It is only about 10,000 light-years in diameter, in comparison to the Milky Way's diameter of 100,000 light years. It is populated by old yellowish stars has four known globular clusters: M54, Arp 2, Terzan 7, and Terzan 8. It should not be confused with the → Sagittarius Dwarf Irregular Galaxy.

→ Sagittarius; → dwarf; → elliptical; → galaxy.

A → dwarf elliptical galaxy that is a satellite of our → Milky Way. It lies about 285,000 → light-years away in the constellation → Sculptor, and has an → absolute magnitude of -11.28 and a mass of about 3 million → solar masses. The Sculptor Dwarf is a → metal-deficient galaxy containing only 4 percent of the oxygen and carbon elements in our own Galaxy.

→ Sculptor; → dwarf; → elliptical; → galaxy.