binary supermassive black hole
siyah-câl-e abar-porjerm-e dorin
Fr.: trou noir supermassif double
A → dual supermassive black hole whose components are separated by a few parsecs.
compact massive galaxy (CMG)
kahkešân-e porjerm-e hampak
Fr.: galaxie massive compacte
A galaxy with a stellar mass of M ≥ 1011Msun and an → effective radius of Re ≤ 1.5 kpc. Many studies have shown that massive galaxies with low → star formation rates were remarkably compact at a → redshift of z≥ 2. At fixed stellar mass of Mstars ≅ 1011Msun, quiescent galaxies are a factor of ~ 4 smaller at z = 2 than at z = 0. As the stellar mass of the galaxies also evolves, the inferred size growth of individual galaxies is even larger. It is unlikely that all massive galaxies in the present-day Universe had a compact progenitor. However, the vast majority of CMGs that are observed at z = 2 ended up in the center of a much larger galaxy today. Their size growth after z = 2 is probably dominated by minor → mergers. Such mergers are expected because other mechanisms cannot easily produce the observed scaling between size growth and mass growth (P. G. van Dokkum1 et al., 2015, ApJ 813, 23).
dual supermassive black hole
siyah-câl-e abar-porjerm-e dogâné
Fr.: trou noir supermassif double
The outcome of a → merger process between two galaxies, each with its own central → supermassive black hole (SMBH), resulting in a remnant galaxy hosting two SMBHs. Simulations of → galaxy mergers show there should be lots of dual → active galactic nuclei (AGN) visible at less than 10 kpc separations. As of 2015 more than 100 known dual supermassive black holes have been found. See also → binary supermassive black hole.
isolated massive star formation
diseš-e vâyutide-ye setâre-ye porjerm
Fr.: formation isolée d'étoile massive
Massive star formation outside → OB associations. Recent observational findings suggest that → massive star formation is a collective process. In other words, massive stars form in → cluster environments and the mass of the most massive star in a cluster is correlated with the mass of the cluster itself. Nevertheless, other observational results give grounds for supposing that massive stars do not necessarily form in clusters but that they can be formed as isolated stars or in very small groups. According to statistical studies nearly 95% of Galactic → O star population is located in clusters or OB associations. This means that a small percentage, about 5%, of high mass stars may form in isolation. Isolation is meant not traceable to an origin in an OB association. This definition therefore excludes → runaway massive stars, which are thought to result from either dynamical interaction in massive dense clusters, or via a kick from a → supernova explosion in a → binary system. Alternatively, isolated massive star has been defined as follows: An O-type star belonging to a cluster whose total mass is < 100 Msun and moreover is devoid of → B stars (Selier et al. 2011, A&A 529, A40 and references therein).
magnetic massive star
setâre-ye porjerm-e meqnâtisi
Fr.: étoile massive magnétique
A → stellar magnetic field associated with
a → massive star.
Magnetic fields are detected only for seven to ten percent of all
studied massive → OB stars, and the
magnetic field occurrence does not depend on the
→ spectral type. Because
these magnetic fields seem to be stable over long time-scales and their
strength does not seem to correlate with known stellar properties, it
is assumed that they are of fossil origin
(→ fossil magnetic field)
and are frozen into the → radiative envelope
of the stars.
The fields are those of the birth
→ molecular clouds, partly trapped inside
the → pre-main sequence star
during the cloud → collapse
phase, possibly further enhanced by a
→ dynamo effect in the early fully convective
Typically, the polar field strength ranges from about a
hundred → Gauss up to several kiloGauss.
However, some weaker fields,
below 100 G, have recently been detected.
Magnetism in Massive Stars (MiMeS)
An international collaboration devoted to the study of the origin and physics of → magnetic fields in → massive stars. The project uses several observatories and a large number of telescopes equipped with → spectropolarimetric and → asteroseismologic instruments, including → HARPS, → HARPSpol, and → ESPaDOnS (Wade et al., 2016, MNRAS 456, 2).
Consisting of or forming a large mass.
From M.Fr. massif (feminine massive) "bulky, solid," from O.Fr. masse "lump."
Porjerm, from por "full, much, very, too much," (Mid.Pers. purr "full;" O.Pers. paru- "much, many;" Av. parav-, pauru-, pouru-, from par- "to fill;" PIE base *pelu- "full," from *pel- "to be full;" cf. Skt. puru- "much, abundant;" Gk. polus "many," plethos "great number, multitude;" O.E. full) + jerm, → mass.
massive black hole
Fr.: trou noir massif
A black hole with a mass between millions and billions of solar masses residing in galactic nuclei. The mass of this type of black holes represents about 0.2% of the bulge mass. When matter is swallowed by the black hole, this gives rise to the tremendous energetic phenomena observed in quasars and active galactic nuclei.
massive close binary
dorin-e kip-e porjerm
Fr.: binaire serrée massive
Fr.: halo massif
Spheroidal distribution of dark matter surrounding a galaxy.
setâre-ye porjerm (#)
Fr.: étoile massive
A star whose mass is larger than approximately 10 → solar masses. The → spectral types of massive stars range from about B3 (→ B star) to O2 (→ O star) and include → Wolf-Rayet stars as well as → Luminous Blue Variables. Massive stars are very rare; for each star of 20 solar masses there are some 100,000 stars of 1 solar mass. Despite this rarity, they play a key role in astrophysics. They are major sites of → nucleosynthesis beyond oxygen and, therefore, are mainly responsible for the → chemical evolution of galaxies. Due to their high ultraviolet flux and powerful → stellar winds, they bring about interesting phenomena in the → interstellar medium, like → H II regions, → turbulence, → shocks, → bubbles, and so on. Massive stars are progenitors of → supernovae (→ type Ia, → type Ic and → type II), → neutron stars, and → black holes. The formation processes of massive stars is still an unresolved problem. For massive stars the → accretion time scale is larger than the → Kelvin-Helmholtz time scale. This means that massive stars reach the → main sequence while → accretion is still going on.
supermassive black hole (SMBH)
Fr.: trou noir supermassif
A → black hole of tremendous mass, equivalent to those of millions or even billions of stars, which is believed to exist and occupy the centers of many galaxies. The supermassive black hole residing in the center of our → Milky Way Galaxy is the object → Sgr A* with a mass of 4 x 106→ solar masses within a radius of 100 → astronomical units.
supermassive neutron star
setâre-ye notroni-ye abar-porjerm
Fr.: étoile à neutron supermassive
Fr.: étoile supermassive
A star with an initial mass over about 120 solar masses. The existence of such stars is the present Universe is not confirmed. Such stars were proposed as an explanation for very bright O type stars in the Large Magellanic Cloud, but these are now known to be clusters of ordinary O stars. → very massive star; → massive star.
very massive star
setâre-ye besyâr porjerm
Fr.: étoile très massive