Galaxies, also known as cosmic islands, in a broad sense refer to an operating system composed of countless stellar systems and dust. Referring to the Milky Way, it is a large galaxy containing stars, gas, cosmic dust and dark matter, and bound by gravity.
Typical galaxies, from dwarf galaxies with tens of millions of stars to elliptical galaxies with trillions of stars, all revolve around the center of mass. In addition to individual stars and thin interstellar matter, most galaxies have a large number of multi-star systems, clusters and various nebulae.
Characteristics of galaxies
Galaxies vary greatly in size. Elliptical galaxies range in diameter from 3,300 light years to 490,000 light years; The diameter of the spiral galaxy is between1.6000 light-years and160000 light-years. Irregular galaxies are about 6,500 to 29,000 light-years in diameter.
The mass of galaxies is generally between 1 100,000 and1trillion times the mass of the sun.
The stars in the galaxy are moving, and the galaxy itself is rotating, and the whole galaxy is also moving in space. Traditionally, astronomers believe that the rotation of galaxies, clockwise and counterclockwise ratio is the same. However, according to the observation results of a distributed participating project of galaxy classification, there are more galaxies rotating counterclockwise.
Most galaxies have the phenomenon of redshift, which shows that these galaxies are getting farther and farther away from the earth in the direction of space line of sight. This is also a strong evidence of the big bang theory.
Galaxies are nearly uniform in large-scale distribution; But on a small scale, it is very uneven. For example, the large Magellanic galaxy and the small Magellanic galaxy form a double galaxy, and they form a triple galaxy with the Milky Way.