What is believed to be the origin of giant elliptical galaxies?


Quick Answer

Giant elliptical galaxies form early in the life of local galactic clusters as members of the group pass close by each other and begin to merge, according to John Dubinski for the Canadian Institute for Theoretical Astrophysics. In any sizable galactic cluster, some galaxies near the core of the group gravitationally interact with each other, exchange material and eventually fall together to form the core of the central elliptical giant.

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Full Answer

Simulations of this process that begin with nothing but spiral galaxies and dwarf ellipticals show that dozens of galaxies quickly migrate to the center of the group and begin "gravitationally harassing" each other. With every pass, the galaxies pull streamers of gas and stars away from their neighbors. In time, the central galaxies organize into an elongated filament with the mass of several dozen spiral galaxies. Over approximately 4.5 billion years, the large filament collapses into a large elliptical galaxy whose constituent stars each have a distinct momentum. The galaxy has no discernible net rotation of its own.

After the large elliptical galaxy takes shape, the cluster enters a stable period that can last hundreds of millions of years. Some galaxies close to the heart of the cluster undergo their own mergers and become ellipticals themselves, while pristine spiral galaxies tend to orbit at the edge of the cluster.

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