ABSTRACT
Active galaxies are an exotic class of galaxies, whose properties are very different in comparison to normal galaxies. Their most striking feature is their nuclei, which is very small and extremely luminous. In some cases, the size of these nuclei may be comparable to that of the solar system. However, their luminosity is typically larger than that of a whole galaxy. Hence these cores generate a huge amount of power in a very compact region and are called Active Galactic Nuclei or AGNs. The host galaxies of AGNs may be one of the normal galaxies, such as a spiral, elliptical, etc. These hosts are often difficult to observe because they are outshined by their nuclei.
