What is a galaxy?
Galaxy is a cluster of stars, nebulae, dark matter and other astronomical objects. Most galaxies have a diameter of tens of thousands of light years and contain billions of stars. Galaxies come in three primary shapes; Spiral galaxies are thin discs, with spiral arms surrounding the central hub; Elliptical galaxies are uniform, oval agglomerations; And irregular galaxies have a small or no definitive structure.
The spiral galaxy concentrates around the bullet, which is roughly spherical and bulges out of the disk. Hub is a Gravity Center of Galaxy and usually contains a supermassive black hole. Surrounding charge are spiral arms that are muscled by wool of stars and gas orbiting the center. Spiral weapons usually have more gas and dust and contain most of the newly created stars that appear blue in color images. The spiral galaxy may have a horizontal stripe passing through its charge; It is assumed that our own galaxy, Milky Way, contains a bar.
elliptical galaxies have a large central hub, but lacks hands of spiral galaxies; They usually look more yellowish in color images from old, reddish stars. Irregular galaxies often do not have a recognizable structure, but can often be recognized as a distorted spiral or elliptical shape. Elliptical and irregular galaxies often result from collisions that cause large explosions of stars formation and distort the structure of galaxies due to complex gravitational interactions. In the end, both galaxies usually combine and create one large galaxy that has threw most of its clouds of gas and dust.
in the visible universe is about one hundred billion galaxies; Most of them are found in large agglomerations called Galaxy Superklustery. Among these super -clubs are cavities with several or no galaxies, often for one hundred million light -years or longer. By studying the rotation of the spiral galaxy AstrThe other people found that most of the matter in the universe were not stars and gas, but invisible "dark matter" that cannot be seen, but still shows gravity. Dark matter is considered to be responsible for these large clusters, because the gravitational attraction of dark matter has attracted the galaxy together.