Understanding the Galaxies and their Radiations

 Galaxies are huge masses of stars, nebulae and interstellar materials. The smallest known galaxies contain about 100,000 stars while the large one contain up to 5,000 billion stars. There are mainly three types of galaxies, classified according to their shape: spiral (arms spiraling outwards from a central bulge), elliptical (oval shaped), and irregular (which have no obvious shape). Sometimes the shapes gets distorted by the collision between galaxies.

 Quasars (quasi-stellar objects) are assumed to be the galactic nuclei but are so far away that their exact nature is still uncertain. They are compact but highly luminous objects in the outer reach of the known universe. The furthest known "ordinary" galaxy is about 12 billion light years away and the furthest known quasar is about 13 billion light years away.

 The active galaxies such as the Seyfert galaxies and radio galaxies emit intense radiations, in the seyfert galaxy the radiation comes from the galactic nuclei and in the radio galaxy the radiation comes from the huge lobes on either side of the galaxy. The radiation from active galaxies and the quasars in caused by the materials falling into central block home.