An Etymological Dictionary of Astronomy and Astrophysics
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The central part of a cluster (globular, galaxies, etc.) where the spatial density of the objects making up the cluster is much higher than the average value.

→ cluster; → core.

The central region of a → massive star where → convection prevails due to steep gradient of temperature relative to pressure.

→ convective; → core.

1) The central region of a star in which energy is generated by → thermonuclear reactions.
2) The central region of a planet or satellite which has a → differentiated interior.
3) The innermost and densest layer of the Earth, lying from 2890 km to 6360 km beneath the surface. It consists primarily of the metals iron and nickel, and is divided into the → outer core, which is believed to be liquid, and the → inner core, which is believed to be solid.
4) The central region of a → star cluster.
5) A flat → density profile representing the distribution of stars in the central region of a galaxy. Cores are found in high mass galaxies. They are believed to result from the interaction of a central → supermassive black hole with another merging black hole.
6) A progenitor of → protostars. → dense core.
7) → reactor core.

Probably from O.Fr. cœur "core of fruit," literally "heart," from L. cor "heart," cf. Gk. kardia: P.Gmc. *khertan- (O.E. heorte, E. heart, Ger. Herz, Bret. kreiz "middle"), Skt. hrd-; Av. zərəd-; Mid.Pers. dil; Mod.Pers. del; Baluci zird; Arm. sirt; PIE base *kerd- "heart".

Maqzé, from maqz "kernel; brain; marrow" + nuance suffix -é. Mod.Pers. maqz from Mid.Pers. mazg "brain; marrow," Av. mazga- "marrow; brain" cf. Skt. majján- "marrow," P.Gmc. *mazga-, O.E. mearg "marrow," Lith. smagenes "brain," O.H.G. mark "marrow," PIE base *mozgho- "marrow, brain".

The collapse of a → massive star's core at the → final → stages of its → evolution when the core consists entirely of → iron (→ iron core). Since iron cannot burn in → nuclear reaction, no energy is generated to support the → gravitational collapse. The result will be a → supernova explosion of → Type Ib, → Type Ic, or → Type II. See also → core-collapse supernova.

→ core; → collapse.

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.

The mass distribution of → pre-stellar cores in → star-forming regions. The CMF is usually represented by dN/dM = M^α, where dM is the mass interval, dN the number of cores in that interval, and α takes different values in different mass ranges. In the case of → low-mass stars, it is found that the CMF resembles the → Salpeter function, although deriving the masses and radii of pre-stellar cores is not straightforward. The observational similarity between the CMF and the → initial mass function (IMF) was first put forth by Motte et al. (1988, A&A, 336, 150), and since then many other samples of dense cores have been presented in this context. For example, Nutter & Ward-Thompson (2007, MNRAS 374, 1413), using SCUBA archive data of the Orion star-forming regions, showed that the CMF can be fitted to a three-part → power law consistent with the form of the stellar IMF. Recent results, obtained using observations by the → Herschel Satellite, confirm the similarity between the CMF and IMF with better statistics (Könyves et al. 2010, A&A, 518, L106; André et al. 2010, A&A, 518, L102). Moreover, these works show that the CMF has a → lognormal distribution (i.e. dN/dlog M follows a → Gaussian form against log M), as is the case for the IMF at low masses (below about 1 solar mass).

→ core; → mass; → function.

→ convective overshooting.

→ core; → overshooting.

A → profile representing the number density of stars in the → core of a galaxy.

→ core; → profile.

A supernova arising from the → core collapse of a → massive star. Same as → Type Ib, → Type Ic, or → Type II supernova.

→ core; → collapse; → supernova.

A → radio-loud quasar in which the central source is enhanced by → relativistic beaming and characterized by a → flat  → spectrum. It has been conjectured that this phenomenon is an → orientation effect. If a radio-loud quasar is seen along its → jet, it will appear as a core-dominated source. See also → lobe-dominated quasar.

→ core; → dominate; → quasar.

A radio galaxy characterized by an emission "halo" surrounding a more intense "core". About 20% of the known extended radio sources are of the core-halo type.

→ core; → halo; → galaxy.

The → mid-infrared radiation which is scattered by unusually large → dust grains in the denser core regions of → molecular clouds. It occurs between 3 and 5 μm, when the light from nearby stars undergoes → scattering by the grains provided that they are about 1 μm in size, instead of 0.1 μm, as previously thought. Coreshine, which was detected in Spitzer IRAC data, is a widespread astronomical phenomenon. It is found across dozens of → dark clouds in the Galaxy and during all the phases of the → low-mass star formation (Pagani et al. 2010, Science, 329, 1622). See also → cloudshine.

→ core; → shine.

An opaque region of a → molecular cloud (A_V  10 mag) which is considered to be the progenitor of → star formation. Dense cores have temperatures of about 10 K and masses of roughly 1 to 10Msun each and in which the → molecular hydrogen density is roughly 10⁴-10⁵ cm^-3 and size 0.1 pc. The → self-gravity of a dense core plays a central part in star formation. See also → hot molecular core.

→ dense; → core.

→ core mass function.

→ dense; → core; → mass; → function.

The innermost part of the Earth consisting of a solid → inner core, mainly composed of → iron, and a → liquid → outer core. The → pressure and → temperature are so extreme that the molten iron solidifies. The temperature at the inner core boundary is expected to be close to the → melting point of iron at 330 gigapascal (GPa). From static laser-heated diamond anvil cell experiments up to 200 GPa, using synchrotron-based fast → X-ray diffraction as a primary melting diagnostic, S. Anzellini et al. (2013, Science 340, 484) conclude that the melting temperature of iron at the inner core boundary is 6230 ± 500 K. This estimation favors a high heat flux at the core-mantle boundary with a possible partial melting of the → mantle. The inner core, 2,400 km in diameter, is suspended in the molten metal of the → outer core, which is about 2,240 km thick. The temperature difference between the mantle and the core is the main engine for large-scale thermal movements, which coupled with the → Earth's rotation, function as a generator for the planet's → magnetic field.

→ Earth; → core.

A first object in → hydrostatic equilibrium predicted to form during early dynamical contraction of a → molecular cloud → clump in the course of the → first collapse.

→ first; → core.

Same as → hot molecular core.

→ hot; → core.

A relatively small, dense, and hot → molecular clump occurring in regions of → massive star formation. HMCs have diameters ≤ 0.1 pc, densities ≥ 10⁷ cm^-3, and temperatures ≥ 100 K. The densest hot cores are traced in → ammonia (NH₃) and possess densities of 10⁸ cm^-3, sizes down to 0.05 pc and temperatures of up to 250 K. Hot molecular cores are generally associated with → compact H II regions and → ultracompact H II regions. High angular resolution observations suggest that HMCs are internally heated by embedded sources, since temperature and density increases toward the center as expected if star formation is occurring close to the core center. Same as → hot core.

→ hot; → molecular; → core.

The central part of the → Earth's core, composed of solidified → iron and → nickel, and extending from a depth of about 5100 km to the center of the Earth, at 6360 km. Its radius is about 1/3 that of the whole core and is effectively decoupled from the → mantle due to the molten nature of the surrounding → outer core. The radius of the inner core is defined by a small increase in → compressional wave velocity at a radius of about 1200 km. Its density is about 12 g/cm³. The → temperature of the inner core has been estimated at 5000-7000 °C.

→ inner; → core.

1) Electromagnetism: A bar of → soft iron that passes through a coil and serves to increase the → inductance of the coil.
2) The innermost part of some planets, such as Mercury, Venus, and Earth, which have a molten iron-rich core.
3) The end point in the evolution of stars with a mass above ~ 10 → solar masses. Such a star evolves in several stages over millions of years during which various → thermonuclear reactions take place in the star core. Each stage results in a core composed of heavier elements. The process ends when → silicon burning produces a core of iron-nickel. Since iron has the maximum → binding energy per → nucleon, the → nuclear fusion cannot proceed further. The iron core shrinks and heats up. It is maintained against → gravitational collapse by → electron degeneracy pressure, but it continues to grow as Si burning adds more iron. When the core reaches its → Chandrasekhar limit, it becomes unstable and undergoes the → core collapse.

→ iron; → core.