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