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When astronomers measured how fast stars orbit the centers of galaxies, they found something puzzling: stars far from the center move almost as fast as those close in. Based on the visible matter alone, they should move much more slowly.
The leading explanation is that galaxies contain large amounts of unseen "dark matter" whose gravity holds them together. Evidence for it also comes from the way galaxy clusters bend light from more distant objects, an effect called gravitational lensing.
According to current estimates, dark matter makes up about 85 percent of the matter in the universe. Yet it does not emit, absorb or reflect light, and no experiment has directly detected it.
Some physicists propose alternative theories that modify our understanding of gravity instead. Determining which explanation is correct remains one of the great open questions in science.
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Worksheets › Grade 12 English › Reading Informational Text › Reading Informational Text
Free Grade 12 English worksheet (Common Core RI.11-12.1): read the informational text "Dark Matter", find the main idea and answer questions with evidence. Skill: Key ideas and details in informational text. Level: Grade 12 — also suits Year 13 (UK).
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Key ideas and details in informational text.
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All 5 reading informational text sheets → · Grade 12 English: all 10 skills → · All Common Core grades
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