Knowra Galaxy rotation curve Galaxy rotation curve A graph of orbital speed versus distance from a galaxy’s center. Its shape reveals how mass and gravity are distributed, including evidence for dark matter.
Circular velocity : The speed required for an object to follow a circular orbit under a given gravitational force. Rotation curves plot this orbital speed at different galactic radii.
NGC 3198 : A nearby spiral galaxy whose extended, nearly flat rotation curve became a classic dark-matter case. Its measured curve remains high well beyond the bright disk.
Keplerian rotation : Orbital motion in which speed declines with radius as expected outside a concentrated central mass. Visible matter alone often predicts this decline where observed curves remain flat.
Dark matter : Matter inferred from gravitational effects that emits, absorbs, and reflects little or no light. Flat rotation curves are among the clearest galactic-scale evidence for it.
Core-cusp problem : The disagreement between predicted steep central dark-matter density profiles and shallower profiles inferred in some galaxies. Inner rotation curves test whether simulated halos have cusps or cores.
Newtonian gravity : A theory in which masses attract with a force proportional to their product and inversely proportional to distance squared. It links orbital speeds to the mass enclosed within each radius.
Andromeda Galaxy : The nearest large spiral galaxy to the Milky Way, located about 2.5 million light-years away. Its rotation has been mapped across stars, gas, and satellite tracers.
Modified Newtonian dynamics : A theory that modifies gravitational dynamics at very low accelerations to explain galactic motions. It explains flat curves without invoking massive dark halos.
Galaxy mass modeling : The inference of a galaxy’s mass distribution from its motions, light, and other observations. Rotation curves are fitted with stellar, gas, and halo contributions.
Missing satellites problem : The mismatch between predicted numbers of small dark-matter subhalos and observed satellite galaxies. Small-galaxy rotation data help test the structure of low-mass halos.
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