Notre Galaxie, La Voie lactée (milky way galaxy)

En tout état de cause, sa forme générale est un disque de 80 000 années-lumière (25 000 pc) de diamètre comportant un bulbe central, lui-même entouré d’un halo sphérique de faible densité de 100 000 al (30 kpc) de diamètre. Elle contient entre 200 et 400 milliards d’étoiles^[7], dont le Soleil, pour une masse totale évaluée de l’ordre de plusieurs centaines de milliards de masses solaires.
Compte tenu de la position très excentrée du Système solaire, les étoiles les plus éloignées de notre galaxie sont distantes d’environ 78 000 al (24 kpc), alors que l’étoile la plus proche du Soleil, Proxima Centauri, se trouve à 4,22 al.

The Milky Way is a barred spiral galaxy 100,000–120,000 light-years in diameter containing 200–400 billion stars. It may contain at least as many planets.^[17] The Solar System is located within the disk, around two thirds of the way out from the Galactic Center, on the inner edge of a spiral-shaped concentration of gas and dust called the Orion–Cygnus Arm. The stars in the inner ≈10,000 light-years are organized in a bulge and one or more bars. The very center is marked by an intense radio source named Sagittarius A* which is likely to be a supermassive black hole. The Galaxy rotates differentially, faster towards the center and slower towards the outer edge. The rotational period is about 200 million years at the position of the Sun.^[8] The Galaxy as a whole is moving at a velocity of 552 to 630 km per second, depending on the relative frame of reference. It is estimated to be about 13.2 billion years old, nearly as old as the Universe. Surrounded by several smaller satellite galaxies, the Milky Way is part of the Local Group of galaxies, which forms a subcomponent of the Virgo Supercluster.