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Lenticular galaxies are in-between elliptical galaxies and spiral galaxies. Lenticular galaxies have a massive center and the arms of a spiral galaxy. These are normally the aftermath of two galaxies merging and creating a new galaxy. They are quite common amongst the many different galaxies.

Irregular galaxies are one of the smallest type of galaxies. They normally don't have a specific shape and are full of dust and gas floating around. Since they have a lot of dust and gas floating around there are a lot of star formations happening in the galaxies. Which make them much brighter than most types of galaxies.

Seyfert galaxies are close to quasars but are less in energy output. They have super massive black holes in the middle and mainly output large amounts of infrared light. The light produced at the center of the galaxy is caused by a super massive black hole's accretion disk heating up to high temperatures.  They are like quasars that have cooled down and aged.

Quasars are the brightest objects in the universe. Most quasars are 1-2 light years across and shine brighter than a galaxy with a diameter of 100,000 light years. Quasars are the early stages of a galaxy and are formed when massive amounts of matter is pulled into the accretion disk of a black hole and the gravitational pull of the black hole creates friction. This then heats the matter up and outputs massive amounts of energy across the electro magnetic spectrum.