Galaxy clusters Dark matter

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strong gravitational lensing observed hubble space telescope in abell 1689 indicates presence of dark matter—enlarge image see lensing arcs.


galaxy clusters particularly important dark matter studies since masses can estimated in 3 independent ways:



from scatter in radial velocities of galaxies within clusters
from x-rays emitted hot gas in clusters. x-ray energy spectrum , flux, gas temperature , density can estimated, hence giving pressure; assuming pressure , gravity balance determines cluster s mass profile.
gravitational lensing (usually of more distant galaxies) can measure cluster masses without relying on observations of dynamics (e.g., velocity).

generally, these 3 methods in reasonable agreement dark matter outweighs visible matter approximately 5 1.







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