Question

There are two classes of explanations for the two major observations concerning Dark Matter. The first class explains Dark Matter as some heretofore unknown massive stuff that we have not been able to detect prior to these observations. The second class of explanations suggests that the current theory of gravity is not true at the scale of galaxies, opening the way for an alternative theory of gravity (Modified Newtonian Dynamics or MOND). In your textbook there is a section about The Bullet Cluster of galaxies being used as a test concerning these two classes. Please tell me which class is supported by these observations and how those observations contradict the other class of explanations?

Answer 1

The bullet cluster of galaxies supports the dark matter theory. For the galaxies to hold together there has to be a much larger mas than the clusters combined and this scientists believe to be somewhat a proof of dark matter.

The bullet cluster contradicts the alternate theory of gravity( MOND ) because even the modified equations(modified gravity theory) cannot account for all the mass in the clusters. Also it was found that the spatial offset of the center of the total mass from the center of the bullet cluster's baryonic mass peaks cannot be explained by the modified gravity thories (MOND).