The nearby or "local" universe, an area that extends about 380
million light-years away from Earth, contains many galaxy
clusters, i.e., gravitationally bound groups of about 100 to
more than 1000 galaxies. These clusters are connected with each
other and make up a huge network of galaxies called the "large-
scale structure" of the Universe. Such configurations raise
fundamental questions: When and how did these structures form in
the history of the Universe? Astronomers think that the Universe
started out as an almost homogeneous mass that spread uniformly.
Small fluctuations in the initial mass distribution increased by
gravity over the 13.7 billion years of the Universe's age and
produced the recent array of clusters. Because clusters contain
a larger number of old and massive galaxies than those found in
isolated galaxies, astronomers speculate that developing
clusters may significantly affect the evolution of their member
galaxies. Therefore, understanding the details of cluster
formation (Note 1) is an e