What Evidence Is There for Considerable Extra Mass Within Galaxies

question 117

Multiple Choice

What evidence is there for considerable extra mass within galaxies that does not produce visible light,the so-called "dark matter?"

• A) The rotation curve of galaxies,showing orbital speeds of material,remains flat to large distances from the galactic centers and does not follow a Keplerian curve.
• B) The appearance of many very dark spots within the galaxy,evidence of numerous low-mass black holes scattered throughout the galaxy
• C) Widespread evidence for gravitational lensing of background stars in a galaxy by massive,but invisible,objects in the foreground
• D) Intense output of X-rays from very hot gas between the stars,originating in otherwise dark regions

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