CAS AS 100 Chapter Notes - Chapter 23: Spiral Galaxy, Doppler Effect, Cosmic Microwave Background
19 May 2016
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23. 1 dark matter: matter that gives off no light. Name given to whatever unseen influence that is causing the gravitational effects. Most of our galaxy"s mass is throughout its halo dark energy: the mysterious force that counteracts gravity. When hubble discovered the expansion, it was assumed that gravity must slow the expansion with time. Evidence now proves that the expansion of the universe is accelerating, implying that a mysterious force counteracts the effects of gravity. We don"t expect to see light from the presence of a force or energy field. *dark energy and matter were proposed because they give the simplest ways to explain observed motions in the universe. ~dark matter has a presumed role as the dominant source of gravity. We can determine the complete distribution of mass in the milky way by measuring the mass of the galaxy with the orbits of the stars at every different distance form the galactic center.
