What makes astronomers think there are black holes in space?
1.when galaxies dissapear, they stop emitting infrared radiation, and a hole in space is formed
2.there are areas of space from which no electromagnetic energy of any kind has been deleted
3.at the end of a star's life cycle, it runs out of hydrogen and stops emitting visible light
4.bursts of light that release large amounts of radio waves precede the formation of a black hole

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human impact on the environment can be seen in the deterioration of the !

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the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.