Astronomy & space · Advanced university
Galaxies, dynamics and dark-matter evidence · revision notes
Galaxies contain stars, gas, dust and other gravitating components. Their morphology does not alone determine all their dynamical properties.
Key ideas and conditions
Structure
Galaxies contain stars, gas, dust and other gravitating components. Their morphology does not alone determine all their dynamical properties.
Dynamics
In a simplified spherical model, circular speed obeys v²=GM(<r)/r. Inferring enclosed mass therefore uses a geometric and dynamical model.
Evidence
Rotation curves, gravitational lensing and other observations constrain mass distributions. The evidence for unseen gravitating components is not a direct photograph of dark matter.
Uncertainty
Inclination, distance, noncircular motion and mass-to-light estimates affect interpretation. Multiple independent probes help test explanations.
Explain without looking
- Does a rotation-curve inference directly identify the microscopic nature of dark matter?
- Name two observational uncertainties relevant to a rotation curve.
Further reading and review references
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