introduction to galaxies

Galaxy is the home for the stars. By star we can indicate many celestial objects (such as Nebula, planets etc.). By Gravitational force of attraction of the total mass they are connected all together.

So, how are the Galaxies formed. There are many different approaches of this particular answer. The famous, among them is Bottom-up theory. In bottom-up theories it is assumed that masses the size of star clusters collapse first, and these then assemble through collisions and mergers into galaxies, clusters of galaxies, and superclusters. The adjacent figure illustrates schematically. The initial collapses are assumed to begin very early in the history of the Universe.

Presence of dark hallo is thought to be there around a galaxy, spherically. Some very old stars remain there, and the orbit they follow, is known as Hallo stars orbit. In the disk of the galaxy the stars in the galaxy follow a certain orbit, known as Disk star orbit (For some variations in kinetical energy the stars use to follow a sinusoidal path being in the Disk star orbit).

Galaxies can be of different types, such as: Elliptical galaxies, Spiral galaxies, Lenticular galaxies. Again the spiral galaxies can be divided in two categories; ‘SA’ and ‘SB’. Mainly we represent the ‘SA’ type as ‘S’. We can further divide ‘S’ and ‘SB’ among some types; such as, ‘Sa’, ‘Sb’, ‘Sc’ and ‘SBa’, ‘SBb’, ‘SBc’.

These types depend on the galactic bulge size. More the compact and bright the bulge is, more the galaxy gets alphabetical priority. An easy way to identify spiral galaxies, is it arms. But if any galaxy is in edge on structure, in our sight, then we can identify them by the row of interstellar-dust of the galaxy. 7 Elliptical galaxies are basically of 8 different types; E0, E1, E2, E3, E4, E5, E6 and E7. The index number defines the changing shape from a circle to ellipse.

Lenticular galaxies are basically the joining point of elliptical and spiral galaxies. Sometime lenticular galaxies are symbolized as S0. In these type of galaxies, loss of interstellar matter, causes it a very little amount of star formation. We can also come to know about some irregular galaxies in the universe, they basically don’t have any shape. Galaxies in together by influence of Gravitational force form a galaxy cluster.

Galaxy clusters again in together form Super clusters. Seyfert galaxies are some kind of galaxies which have an active nucleus. It radiates enormous amount of energy, due to its high spin of the core region. Hoag's Object is a non-typical galaxy of the type known as a ring galaxy; such as: PGC 54559.