Two Hypotheses For Origins
Dwarf ellipticals may be primordial objects. Within the currently favoured cosmological Lambda-CDM model, small objects (consisting of dark matter and gas) are the first to form. Because of their mutual gravitational attraction, some of these will coalesce and merge, forming more massive objects. Further mergers lead to ever more massive objects.
The process of coalescence is thought to lead to the present-day galaxies, and has been called "hierarchical merging". If this hypothesis is correct, dwarf galaxies may be the building blocks of today's giant galaxies.
An alternative suggestion is that dEs could be the remnants of low-mass spiral galaxies that obtained a rounder shape through the action of repeated gravitational interactions with giant galaxies within a cluster. This process of changing a galaxy's morphology by interactions has been called "galaxy harassment". Evidence for this latter hypothesis has been found in the form taken by stellar disks and spiral arms of spiral galaxies. Under this alternative hypothesis the disks and arms are modified version of the original stellar disk of the transformed spiral galaxy, and similarly, small remnants of disks and arms are embedded within "harassed" dEs.
Read more about this topic: Dwarf Elliptical Galaxy
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