markaz-e kahkešân (#)
Fr.: centre galactique
1) The rotational center of the → Milky Way galaxy located
in the direction of the → Sagittarius constellation at a
distance of 7.62 ± 0.32 kpc (2005, ApJ 628, 246). Its equatorial coordinates
(J2000 epoch) are: R.A. 17h45m40.04s, Dec. -29° 00' 28.1''.
The Sun orbits around the Galactic center once every 200 million years
at a speed of 220 km per second. It is believed that
there is a → supermassive black hole at the
Galactic center cluster
xuše-ye markaz-e kahkešân
Fr.: amas du centre galactique
One of the three massive clusters located toward the → Galactic center: → Quintuplet cluster, → Arches cluster, → Central cluster. Heavily extinguished by the presence of dust clouds and only accessible at infrared (and longer) wavelengths or in X-rays, each of these clusters has a population of more than a hundred → massive stars. The three clusters are similar in most respects, each containing about 104 solar masses in stars. The Arches cluster is younger than the two others.
xuše-ye kahkešâni, ~ kahkešânhâ
Fr.: amas galactique
Fr.: coordonnées galactiques
A system of astronomical coordinates using → latitude (bII) measured north and south from the → Galactic equator and → longitude (lII), measured from the → Galactic Center in the sense of increasing → right ascension from 0 to 360 degrees. In the old system (lI,bI), the Galactic center was at lI = 327°41'. Same as → galactic system.
Fr.: disque galactique
Fr.: dynamique galactique
Fr.: équateur galactique
The great circle in the sky defined by the place of the → Galactic plane or the → Milky Way. At an angle of about 62°, the Galactic equator intersects the celestial equator at two points located in the constellations → Monoceros and → Aquila.
Galactic habitable zone
zonâr-e zistpazir-e kahkešân
Fr.: zone habitable galactique
A region of the Galaxy whose boundaries are set by its calm and safe environment and access to the chemical materials necessary for building terrestrial planets similar to the Earth. → circumstellar habitable zone; → habitable zone.
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.