What puzzle do the orbital velocities of stars and gas in spiral galaxies present to modern astrophysics?
Answer
The resulting rotation curve refuses to follow simple Newtonian gravity predictions based only on visible light.
The fundamental issue in galactic dynamics centers on the plot of orbital velocities versus distance from the core, known as the rotation curve. When astronomers map these speeds, the resulting graph consistently contradicts what calculations based purely on the mass of luminous matter (stars, gas, dust) should yield under the rules of Newtonian gravity. The deviation is stubborn: instead of showing the expected decrease in speed with increasing radius, the curve flattens out, creating a profound puzzle regarding the source of the required gravitational pull.
Related Questions
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