What process leads to the massive size and extreme gas depletion observed in the largest elliptical galaxies?

Answer

Repeatedly absorbing or merging with smaller galaxies

The largest elliptical galaxies are believed to have grown through continuous accretion and merging, which results in massive structure formation and the consumption or loss of interstellar gas.

What process leads to the massive size and extreme gas depletion observed in the largest elliptical galaxies?
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