An Etymological Dictionary of Astronomy and Astrophysics
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A region in the → interstellar medium where processes of → star formation are going on or have occurred in the past.

→ star; → formation; → region.

The time necessary for a star to form. It depends inversely on the stellar mass.

→ star formation; → time scale.

A → main sequence→ B-type star that orbits the → supermassive black hole candidate → Sgr A* in the → Galactic center. The star S2, which is bright enough for making detailed measurements, has a highly elliptical, 16-year-period orbit around Sgr A*. Near → pericenter at 120 → astronomical units, ~ 1400 → Schwarzschild radii, the star has an orbital speed of ~ 7650 km s^-1, such that the first-order effects of → special relativity and → general relativity have become detectable with current capabilities (Auber et al., 2018, A&A 615, L15).

→ star.

Same as → stellar system.

→ stellar; → system.

A curved → path left by a star on an → imaging detector attached to a → telescope when the telescope does not keep up with the → rotation of the → Earth.

→ star; → trail.

A galaxy that is located on the → galaxy main sequence in the plane relating → star formation rates to total stellar masses.

→ star; → formation; → galaxy.

A region in which → star formation is going on.

→ star; → formation; → region.

Simultaneous formation of a large number of stars in a region of a galaxy at an exceptionally high rate, compared to the usual star formation rates seen in most galaxies.

→ star; → burst.

A galaxy showing a short-lived intense period of star formation that is unsustainable over the → Hubble time due to the limited supply of gas within a galaxy. Starburst galaxies were first classified by Searle & Sargent (1972) and Searle et al. (1973), based on the blue colors produced by the → massive stars formed during the burst. In the local Universe, starbursts create approximately 10% of the radiant energy and 20% of the massive stars. At z = 1, starburst characteristics are found in 15% of galaxies, presumably attributable to the greater amounts of gas typically present in young galaxies and increased galactic interactions. The starburst's impact on a galaxy and the surrounding → intergalactic medium is primarily due to the consumption of gas that fuels the burst and the feedback from massive stars formed in the burst (McQuinn et al. 2010, astro-ph/1008.1589).

→ starburst; → galaxy.

The → splitting of spectral lines of atoms and molecules due to the presence of an external electric field, which slightly changes the → energy levels of the atom. → Zeeman effect.

Named after Johannes Stark (1874-1957), a German physicist, and Physics Nobel Prize laureate (1919); → effect.

An astrophysical phenomenon that occurs when the → crust of a → neutron star undergoes a sudden adjustment, analogous to an → earthquake on Earth. Starquakes are thought to be caused by huge → stresses exerted on the surface of the neutron star produced by twists in the ultra-strong interior → magnetic fields. They are thought to be the source of the intense → gamma-ray bursts that come from → soft gamma repeaters.

→ star; → quake.

A phenomenon similar to a → sunspot but occurring on the surface of a star other than Sun. Due to spatial resolution constraints, starspots so far observed are in general much larger than those on the Sun, up to about 30% of the stellar surface may be covered, corresponding to sizes 100 times greater than those on the Sun.

→ star; → spot.

A process in which a star is not formed spontaneously but is provoked by the action of external forces, such as pressure and shock on a molecular cloud by close-by → massive stars, → supernova explosions, etc. See also → sequential star formation.

Stimulated, p.p. of → stimulate; → star formation.

A mechanism that could be responsible for global → spiral structure in galaxies either by itself or in conjunction with spiral → density waves. In this mechanism, star formation is caused by → supernova-induced → shocks which compress the → interstellar medium. The → massive stars thus formed may, when they explode, induce further → star formation. If conditions are right, the process becomes self-propagating, resulting in agglomerations of young stars and hot gas which are stretched into spiral shaped features by → differential rotation. Merging of small agglomerations into larger ones may then produce large-scale spiral structure over the entire galaxy. The SSPSF model, first suggested by Mueller & Arnett (1976) was developed by Gerola & Seiden (1978). While the → density wave theory postulates that spiral structure is due to a global property of the galaxy, the SSPSF model examines the alternative viewpoint, namely that spiral structure may be induced by more local processes. The two mechanisms are not necessarily mutually exclusive, but they involve very different approaches to the modeling of galaxy evolution. The SSPSF gives a better fit than the density wave theory to the patchy spiral arms found in many spiral galaxies. However, it cannot explain → galactic bars.

→ stochastic; → self; → propagate; → star; → formation.

A star that is less luminous than a main-sequence star of the same spectral type.

→ sub-; → luminous; → star.

A group of hundreds to thousands of very young stars packed into an unbelievably small volume of a few parsecs in size. These objects represent the youngest stage of → massive star cluster evolution yet observed. The most massive and dense SSCs, with ages less than 10⁶ years, may be proto globular clusters. SSCs are thought to dissolve within 10 million years and merge into the field star population.

→ super; → star; → cluster.

A star whose mass exceeds the → canonical upper limit of the stellar → initial mass function (Kroupa et al. 2012, arXiv:1112.3340).

→ super-; → canonical; → star.

A very → metal-rich star whose iron → metallicity, [Fe/H], exceeds 0.20 → dex. Examples include HD 32147, HD 121370, and HD 145675 (Feltzing & Gonzalez, 2001, A&A 367, 253).

→ super-; → metal; → rich; → star.

A highly luminous → B[e] star with a luminosity greater than 10⁴L_sun. A number of such objects exist in the → Magellanic Clouds, e.g. LMC R126, R66, SMC R4, and R50. A likely example in our Galaxy is MWC 300.

→ supergiant; → B[e] star.

A → neutron star of mass above the typical value that is temporarily prevented from → collapseing into a → black hole because of its rapid → rotation.

→ supermassive; → neutron; → star.