How do the observed rotational velocities of stars and gas behave in the outskirts of spiral galaxies compared to predictions?
Answer
They remain surprisingly constant, or flat, as they move outward.
Astronomical observations consistently reveal that the measured rotational velocities of stars and gas clouds do not exhibit the expected Keplerian decline when measured far from the galactic center. Instead of slowing down as the density of visible stars dramatically decreases, the measured speeds remain nearly the same, showing a remarkably flat rotation curve. This constancy is observed hundreds of thousands of light-years out, long after the contribution from the luminous matter should have caused a significant drop-off in orbital speed according to standard gravitational expectations based only on light sources.
Related Questions
What is the expected relationship for orbital velocity (v) versus radius (r) in a spiral galaxy containing only visible matter?How do the observed rotational velocities of stars and gas behave in the outskirts of spiral galaxies compared to predictions?What mass distribution M(r) is mathematically required for the orbital speed v to remain constant (v \approx constant)?In the Milky Way example, what does the mass discrepancy at 50 kpc imply about the unseen component?What mechanism does Modified Newtonian Dynamics (MOND) propose to explain flat rotation curves?What puzzle do the orbital velocities of stars and gas in spiral galaxies present to modern astrophysics?Over what enormous scale have observations confirmed the flatness of the rotation curve persists?Which solar system object comparison illustrates why mass concentrated near the center predicts a speed decline with distance?What specific function does the inferred Dark Matter halo serve regarding outlying stars in spiral galaxies?What required consistency check must both Dark Matter and modified gravity models pass regarding galaxy properties?