Fr.: halo galactique
A roughly spherical aggregation of → globular clusters, as well as the oldest stars and unseen mass that surrounds the Galaxy.
Fr.: latitude galactique
In the → Galactic coordinate system, the angle between the line of sight to an object and the → Galactic equator. Galactic latitude, usually represented by the symbol bII, ranges from +90 degrees to -90 degrees.
Fr.: longitude galactique
In the → Galactic coordinate system, the angle between the → Galactic Center and the projection of the object on the → Galactic plane. Galactic longitude, usually represented by the symbol lII, ranges from 0 degrees to 360 degrees.
Fr.: noyau de galaxie
A concentration of stars and gas in the innermost region of a galaxy, sometimes extending over thousands of light-years from the center of the galaxy.
Fr.: flot galactique
Fr.: plan galactique
Fr.: pôle galactique
The point on the sky, north or south, at which the galaxy's rotation axis would meet the celestial sphere.
Galactic radio noise
nufe-ye râdioi-ye kahkešân
Fr.: bruit radio de la Galaxie
A diffuse radio signal that originates outside the solar system. It is strongest in the direction of the Galactic plane.
Fr.: rotation galactique
The revolving of the gaseous and stellar content of a galaxy around its central nucleus. The rotation is not uniform, but differential. One revolution of the Sun within our own Galaxy takes about 220 million years, or one cosmic year.
Fr.: structure galactique
The global shape and the arrangement of the various parts or constituents of a galaxy.
Fr.: système galactique
Same as → galactic coordinates.
Fr.: vent galactique
An outflow of hot gas, analogous to the → solar wind, from a galaxy that has recently undergone a high → burst of star formation or has an → active galactic nucleus. Galactic winds are streams of high speed charged particles blowing out of galaxies with speeds of 300 to 3,000 km s-1. In the case of starbursts, galactic winds are powered by → stellar winds driven by → massive stars and → supernova explosions. Galactic winds contain a mixture of extremely hot metal-enriched supernova ejecta and cooler entrained gas and dust. Outflowing material has been observed at great distances from galaxies (10 to 100 kpc). In some cases they escape the galaxy potential well and pollute the → intergalactic medium with → heavy elements. A prominent example is the → superwind of the starburst galaxy M82.
Fr.: fenêtres galactiques
The regions near the Galactic plane where there is low absorption of light by interstellar clouds so that some external galaxies may be seen through them.
sâl-e kahkešâni (#)
Fr.: année galactique
The time taken for the Sun to revolve once around the center of the Milky Way, amounting to about 220 million years.
ostacân bâ marpel-e kahkešâni
Fr.: flot à l'échelle galactique
The enormous amounts of → mass and → energy released from active galaxies into the → intergalactic medium. → Supermassive black holes, believed to exist at the centres of active galaxies (→ active galaxy), → accrete matter and liberate huge quantities of energy. The energy output is often observed as → active galactic nuclei (AGN) outflows in a wide variety of forms, e.g. → collimated → relativistic jets and/or huge overpressured cocoons in → radio, → blueshifted broad → absorption lines in the → ultraviolet and → optical, → warm absorbers and ultrafast outflows in → X-rays, and → molecular gas in → far infrared. Moreover, the processes of → star formation and → supernova explosions release mass/energy into the surroundings. This → stellar feedback heats up, ionizes and drives gas outward, often generating large-scale outflows/→ winds. Galactic outflows are observed at low redshifts reaching a velocity as large as 1000 km s-1 and at high-z up to z ~ 5, sometimes extending over distances of 60-130 kpc. Galactic-scale outflows may be a primary driver of galaxy evolution through the removal of cool gas from star-forming regions to a galaxy's → halo or beyond.
Fr.: absorption intergalactique
Fr.: nuage intergalactique
→ Intergalactic matter in the form of clouds.
Fr.: matière intergalactique
Very low density material found indirectly in the space between galaxies. → intergalactic absorption.
Fr.: milieu intergalactique
The matter or environment between the galaxies of a → cluster.