In 2003 two astronomers Puraga Guha Thakurta of UCSC and David Reitzel of UCLA presented new findings to the American Astronomical Society. They believed that other galaxies grow by cannibalism. This means that large galaxies merge with smaller galaxies which creates a bigger galaxy.
NASA has captured a rare example of this happening more than 90 million light-years away. Hubble Space Telescope caught a picture of an elliptical galaxy that is considered a “shell galaxy” that shows unusual symmetry. These are formed when larger galaxies take over smaller ones creating a newly-combined galaxy.
Another type of galaxy that is found when this occurs is an irregular galaxy. This means that the galaxy has an irregular shape and does not fall into regular classes of galaxies. Examples of these include Whirlpool Galaxy, Mice Galaxies, and Andromeda Galaxies. These galaxies all seem to be merging and Cannibalizing to become larger.
The hierarchical model of galaxy formation galaxies is believed to grow by eating smaller, dwarf galaxies. In this model, some of these dwarf galaxies are shredded by the gravitational forces when they get too close to the halo. When this occurs it leaves streams of stars behind as evidence of the original event.
One noteworthy fact is the Andromeda Galaxy, is the largest galaxy Local Group and is on its way to the Milky Way. Andromeda boasts over a trillion stars while our galaxy has half a trillion. This is a very distant future event if it happens at all since Andromeda is 4.5 billion years away.
Galactic Cannibalism is becoming more common as the universe changes. There have been many interactions of this observed by the Hubble Space Telescope. There is substantial evidence that both Andromeda and Milky Way have done this many times. In 2 million years or so when the galaxies fly past each other, there is a chance the streams of stars behind them will cause a collision creating one giant galaxy.
This is a one in ten chance of happening, and if it does Earth may not even be around.
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