Basically there are 3 types of galaxies, that are elliptical, spiral and irregular.
Elliptical Galaxies :-
These systems exhibit certain characteristic properties. They have complete rotational symmetry; i.e., they are figures of revolution with two equal principal axes. They have a third smaller axis that is the presumed axis of rotation.
Unlike spiral galaxies, elliptical galaxies are not supported by rotation. The orbits of the constituent stars are random and often very elongated, leading to a shape for the galaxy determined by the speed of the stars in each direction. Faster moving stars can travel further before they are turned back by gravity, resulting in the creation of the long axis of the elliptical galaxy in the direction these stars are moving.
The size of an elliptical galaxy is measured as an effective radius which corresponds to the size of a circle encompassing half of the light coming from the galaxy. Measurements reveal that elliptical galaxies come in a large range of sizes, from the rare giant elliptical found in the center of galaxy clusters and stretching over hundreds of kilo parsecs, to the very common dwarf elliptical which may have diameters as small as 0.3 kilo parsecs.
Giant elliptical galaxies are generally thought to be the result of galaxy mergers. Ordinary elliptical galaxies may also form in this manner, or may have formed from the gravitational collapse of an interstellar gas cloud. In this case, a rapid burst of star formation would convert almost all the gas into stars simultaneously, leaving nothing to form a disk. Dwarf elliptical may also form in this manner, but others have suggested that they form out of the leftover material of a larger galaxy or in the tidal tails of interacting galaxies.
Spiral Galaxies :-
Spiral galaxies are twisted collections of stars and gas that often have beautiful shapes and are made up of hot young stars. Most of the galaxies that scientists have discovered so far are spiral galaxies, as opposed to the other two main categories of galaxy shapes — elliptical and irregular.
The Milky Way – the galaxy that includes Earth and our solar system – is an example of a spiral galaxy.
They are divided into two parallel classes: normal spirals and barred spirals. The normal spirals have arms that emanate from the nucleus, while barred spirals have a bright linear feature called a bar that straddles the nucleus, with the arms unwinding from the ends of the bar. The nucleus of a spiral galaxy is a sharp-peaked area of smooth texture, which can be quite small or, in some cases, can make up the bulk of the galaxy. Both the arms and the disk of a spiral system are blue in color, whereas its central areas are red like an elliptical galaxy.
Irregular Galaxies :-
Irregular galaxies are often chaotic in shape, with no central bulge or spiral arms. Although they used to have a more familiar shape, a dramatic collision with another galaxy has distorted their shape.Most representatives of this class consist of grainy, highly irregular assemblages of luminous areas. They have neither noticeable symmetry nor an obvious central nucleus, and they are generally bluer in color than are the arms and disks of spiral galaxies. An extremely small number of them, however, are red and have a smooth, though non symmetrical, shape.
Follow Our Instagram For Such Nice Posts click here.
0 Comments