slow-moving massive particles, not yet identified, that don’t absorb, emit, or reflect light or other electromagnetic radiation
the assumption that, on the large scale, the universe at any given time is the same everywhere—isotropic and homogeneous
an energy that is causing the expansion of the universe to accelerate; the source of this energy is not yet understood
changes in individual galaxies over cosmic time, inferred by observing snapshots of many different galaxies at different times in their lives
a process by which a larger galaxy strips material from or completely swallows a smaller one
having a consistent and even distribution of matter that is the same everywhere
massive particles, not yet identified, that don’t absorb, emit, or reflect light or other electromagnetic radiation; hot dark matter is faster-moving material than cold dark matter
the same in all directions
a small cluster of galaxies to which our Galaxy belongs
a collision between galaxies (of roughly comparable size) that combine to form a single new structure
a galaxy or merger of multiple galaxies that turns gas into stars much faster than usual
a large region of space (more than 100 million light-years across) where groups and clusters of galaxies are more concentrated; a cluster of clusters of galaxies
a region between clusters and superclusters of galaxies that appears relatively empty of galaxies