akankshasoneja wrote:
Couldn't get Q117..Can some give a detailed explanation please
hi
117. The authors suggestion that as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth (lines 3437) would be most weakened if which of the following were discovered to be true?
(A) Spiral galaxies are less common than types of galaxies that contain little nonluminous matter.
(B) Luminous and nonluminous matter are composed of the same basic elements.
(C) The bright nucleus of a typical spiral galaxy also contains some nonluminous matter.
(D) The density of the observable universe is greater than most previous estimates have suggested.
(E) Some galaxies do not rotate or rotate too slowly for their rotational velocity to be measured.
see the author is concluding:
Our findings suggest that as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth.
(last para 1st line)
what is the basis of this conclusion:
It has been known for some time that outside the bright nucleus of a typical spiral galaxy luminosity falls off rapidly with distance from the center. If luminosity were a true indicator of mass, most of the mass would be concentrated toward the center. Outside the nucleus the rotational velocity would decrease geometrically with distance from the center, in conformity with Keplers law. Instead we have found thatthe rotational velocity in spiral galaxies either remains constant with increasing distance from the center or increases slightly.This unexpected result indicates that the falloff in luminous mass with distance from the center is balanced by an increase in nonluminous mass.
so author experiment is onTYPICAL galaxy ==>some results came==>then he concluded.
see the flaw is he is considering only a limited source of galaxy and generalising for whole universe.
so the ultimate weakener that is option B:
Spiral galaxies are less common than types of galaxies that contain little nonluminous matter.
SO this is saying that typical spiral galaxy are less number hence whatever conclusion author is trying to make can be wrong.
hope it helps