What key compositional element is notably lacking in Elliptical galaxies compared to Spirals?
Answer
Cold gas and dust, the raw materials for star creation
The most fundamental distinction between spiral galaxies and elliptical galaxies, aside from shape, lies in their interstellar medium content, which dictates their evolutionary state. Elliptical galaxies, often thought to be the end products of major mergers, possess very little cold gas and dust. This scarcity means they have either consumed or ejected the necessary raw materials, resulting in very low or nonexistent ongoing star formation—they are quiescent. In contrast, spiral galaxies maintain vast reservoirs of this cold gas and dust within their disks, allowing them to remain active sites of star birth, producing younger, hotter stars.
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