List three pieces of evidence that support the existence of interstellar matter (not dark matter) even in regions where we do not observe nebulae. cdescribe why energy must flow in stars and describe two ways in which it can flow in normal stars. list three reasons why pulsars are not always associated with supernova remnants. list the most compelling evidence (in your opinion) for the big bang. provide a brief argument to support your choice of evidence as the most compelling. name three spiral tracers and explain why they have to be short lived. provide a brief summary of the argument used to first convincingly show that the solar system is not in the central region of the galaxy.