Process of Science: Evidence for dark matter in galaxy clusters ...

[rmenurse]

Process of Science: Evidence for dark matter in galaxy clusters can be seen in observations of the motions of individual galaxies, X-ray observations of hot intra-cluster gas, and gravitational lensing.
 
  What is different about lensing that further strengthens the case that dark matter really does exist.

Question 2

How do disk stars orbit the center of the galaxy?
 
  A) They all orbit in roughly the same plane and in the same direction.
  B) They have orbits randomly inclined and in different directions relative to the galactic center.
  C) They follow spiral paths along the spiral arms.
  D) They follow orbits that move up and down through the disk, typically taking them about 50,000 light-years above and below the disk on each orbit.

[aloop]

Answer to Question 1

Gravitational lensing provides a mass estimate that is not derived using Newton's laws of motion. Thus a possible argument that Newton's laws do not apply on the scales of galaxy clusters does not negate all the lines of evidence for dark matter. (Moreover, the fact that gravitational lensing gives the same answer as the other methods is evidence that Newton's laws are in deed applicable on these scales.)

Answer to Question 2

A

[rmenurse]

Thanks

[aloop]

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