Milky Way


May 28, 2022

The Milky Way (Galaxy) is a spiral galaxy that contains the Earth and the solar system. The radius of the stellar disk of the Milky Way and the radius of the Galaxy are 16 kiloparsecs. The total mass of the Galaxy, taking into account dark matter, is estimated as 1–2⋅1012 M⊙. The Milky Way contains from 100 to 400 billion stars, and its luminosity is 2⋅1010 L⊙. Compared to other spiral galaxies, the Milky Way has a fairly large mass and high luminosity. The solar system is located at a distance of 7.5-8.5 kiloparsecs from the center of the Galaxy and moves around it at a speed of 220 km/s. All stars visible to the naked eye belong to our galaxy, but often the term "Milky Way" is applied to a light hazy band in the night sky. Due to the fact that the Earth is inside the Milky Way, the exact view of our Galaxy from the outside is unknown. Most of the stars in the galaxy are concentrated in the galactic disk with spiral arms. It also contains a medium-sized bulge and a moderately pronounced bar, and according to the morphological classification, it is classified as SBbc or SABbc. In addition, the disk of the Milky Way is surrounded by a galactic halo, which contains a small proportion of stars and a large amount of hypothetical dark matter. There is a supermassive black hole at the center of the Galaxy. In the Milky Way, the rate of star formation is 1.6–2 M⊙ per year. In a simplified form, the stellar population of the Galaxy can be divided into population I and population II. The former consists of relatively young, high-metallicity stars that move in near-circular orbits and form a flat rotating galactic disk. The second is old stars, poor in heavy elements, which move along elongated orbits and make up a spheroidal halo that does not rotate as a whole, and a bulge. Interstellar gas and open star clusters belong to population I, while globular clusters belong to population II. More accurate is the division of the stellar population into subsystems of a thick and thin disk, halo and bulge separately. The different subsystems of the galaxy also have different dynamics: the flatter subsystems rotate faster and have less velocity dispersion. The Milky Way is located