What is the unavoidable conclusion drawn from a galaxy rotation curve that refuses to drop off at large radii?
Answer
Galaxies contain vastly more mass than can be accounted for by their light.
The necessary gravitational pull required to maintain high outer orbital speeds implies the existence of mass that emits no detectable light across the electromagnetic spectrum, leading to the concept of dark matter.
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Astrophysics: Galaxy Rotation Curves and Dark Matter - YouTube
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