KarishmaB GMATNinjaHi Experts,
Even after reading all the explanation, I couldn't understand why D over B in 116. Please help.
116. The authors’ study indicates that, in comparison with the outermost regions of a typical spiral galaxy, the region just outside the nucleus can be characterized as having
(B) lower rotational velocity and higher luminosity
(D) similar rotational velocity and higher luminosity
I agree that luminosity would be higher in the region just outside nucleus compared with the outermost region.
According to this line "we have found that the rotational velocity in spiral galaxies either remains constant with increasing distance from the center or increases slightly"
So if velocity could either remains constant or increasing with distance, so region just outside nucleus will have lower velocity compared with the outermost region. How to choose between "lower" or "similar" velocity? I think both are true.
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 34–37) would be most weakened if which of the following were discovered to be true?
(D) The density of the observable universe is greater than most previous estimates have suggested.
How to reject D?
If the density of observable universe is higher, more luminous mass exist. So less dark matter exist or needed. Why this reasoning is incorrect?
Thank you so much for your time