Tracer galaxies probe the cosmic background

The universe, perhaps surprisingly, is not comprised of galaxies randomly distributed throughout space; that is, it is not very homogeneous. Instead, its galaxies are clustered into distinct structures, typically gigantic filaments separated by vast voids—the "large-scale structure (LSS)," an architecture whose discovery and mappings were pioneered by CfA astronomers about thirty years ago. Astronomers since have combined LSS maps with results from the cosmic microwave background radiation (CMBR) and ideas about the inflationary big bang to assemble a remarkably consistent picture of the universe, its origins and its evolution.

source https://www.lifetechnology.com/blogs/life-technology-news-blog/tracer-galaxies-probe-the-cosmic-background