<Ul> <Li> Minor merger: It occurs when one of the galaxies is significantly larger than the other (s). The larger galaxy will often "eat" the smaller, absorbing most of its gas and stars with little other major effect on the larger galaxy . Our home galaxy, the Milky Way, is thought to be currently absorbing smaller galaxies in this fashion, such as the Canis Major Dwarf Galaxy, and possibly the Magellanic Clouds . The Virgo Stellar Stream is thought to be the remains of a dwarf galaxy that has been mostly merged with the Milky Way . </Li> <Li> Major merger: It takes place if two spiral galaxies that are approximately the same size collide at appropriate angles and speeds, they will likely merge in a fashion that drives away much of the dust and gas through a variety of feedback mechanisms that often include a stage in which there are active galactic nuclei . This is thought to be the driving force behind many quasars . The end result is an elliptical galaxy, and many astronomers hypothesize that this is the primary mechanism that creates ellipticals . </Li> </Ul> <Li> Minor merger: It occurs when one of the galaxies is significantly larger than the other (s). The larger galaxy will often "eat" the smaller, absorbing most of its gas and stars with little other major effect on the larger galaxy . Our home galaxy, the Milky Way, is thought to be currently absorbing smaller galaxies in this fashion, such as the Canis Major Dwarf Galaxy, and possibly the Magellanic Clouds . The Virgo Stellar Stream is thought to be the remains of a dwarf galaxy that has been mostly merged with the Milky Way . </Li> <Li> Major merger: It takes place if two spiral galaxies that are approximately the same size collide at appropriate angles and speeds, they will likely merge in a fashion that drives away much of the dust and gas through a variety of feedback mechanisms that often include a stage in which there are active galactic nuclei . This is thought to be the driving force behind many quasars . The end result is an elliptical galaxy, and many astronomers hypothesize that this is the primary mechanism that creates ellipticals . </Li> <P> One study found that large galaxies merged with each other on average once over the past 9 billion years . Small galaxies were coalescing with large galaxies more frequently . Note that the Milky Way and the Andromeda Galaxy are thought to collide in about 4.5 billion years . The merging of these galaxies would classify as major as they have similar sizes . The result would therefore be an elliptical galaxy . </P>

Two mechanisms that cause the number of stars in a galaxy to increase