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Astronomy 2e

Key Terms

Astronomy 2eKey Terms
cold dark matter
slow-moving massive particles, not yet identified, that don’t absorb, emit, or reflect light or other electromagnetic radiation
cosmological principle
the assumption that, on the large scale, the universe at any given time is the same everywhere—isotropic and homogeneous
dark energy
an energy that is causing the expansion of the universe to accelerate; the source of this energy is not yet understood
evolution (of galaxies)
changes in individual galaxies over cosmic time, inferred by observing snapshots of many different galaxies at different times in their lives
galactic cannibalism
a process by which a larger galaxy strips material from or completely swallows a smaller one
homogeneous
having a consistent and even distribution of matter that is the same everywhere
hot dark matter
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
isotropic
the same in all directions
Local Group
a small cluster of galaxies to which our Galaxy belongs
merger
a collision between galaxies (of roughly comparable size) that combine to form a single new structure
starburst
a galaxy or merger of multiple galaxies that turns gas into stars much faster than usual
supercluster
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
void
a region between clusters and superclusters of galaxies that appears relatively empty of galaxies
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