Galaxy

 Galaxy

Galaxies are huge congregation all stars held Together by force of gravity. They are so big that they are also called Island Universe. Studies of distant spaces with optical and radio telescope indicate that there may be about 1.3 trillion galaxies in the visible Universe. Galaxies seems to be scattered in space. Galaxies tend to be grouped together into clusters, and some clusters appear to be grouped into superclusters all the galaxies will look at all display red shift in their Spectra indicating they are moving from from us. Current data suggest that the Galaxies are moving apart at rate of 50-100 KPS for every million parsecs of distance. 

When the expanding when the expanding material of the universe broke up in the first instance billions of Island of gaseous matters were formed in space these gases Island or Proton Galaxy is rotated each with its own speed of rotation those with very low rotational speed as you and nearly spherical shapes. Others assumed elliptical forms with varying degrees of elongation depending on the rotational Speed most of these gases islands, however had such rotational speed that their bodies were flatened out into the shape of discs from whose edges spiral arms streamed. The centre of the galactic disc was formed by a multitude of proto-starts rotating on regular circular orbits around the centre of the galaxy , whereas the spiral arms were formed by highly diluted , dusty gas streamers which were caught in the general rotation and were twisted into the shape of spirals . The galaxies have thus come out in different shapes and sizes.

A structural analysis of the known galaxies bring out three major forms spiral, elliptical and irregular spiral. Spiral have a Central nucleus with great spiral arms training round it. The Milky Way and the Andromeda Galaxy belong to this group a special type of spiral galaxies in what are called Barred spirals which have a central bar as nucleus. The spiral comprise some 80% of the Galaxy sorry far known. Elliptical galaxies show purely elliptical shape without any spiral arms . They range in shape from spherical ellipticals to extremely saucers-shaped ones and account for about 17%of the known galaxies. Irregular , as the name suggest , show no definite geometric pattern or shape.