How do scientists know that dark matter exists?

Question

A. They notice that light seems to “disappear” in certain areas of galaxies.
Something has to be there to form superclusters; gravity alone wouldn’t do it.
C. It’s the only explanation for the redshifts phenomenon seen in some celestial objects.
D. They observe gravitational lensing bending the light of other objects in space.

Answer 1

Scientists have several lines of evidence for the existence of dark matter, and among the options you've provided, the most compelling ones are:

B. Something has to be there to form superclusters; gravity alone wouldn’t do it. This statement reflects the observation that galaxies and galaxy clusters exhibit mass distributions that cannot be accounted for by visible matter alone. The gravitational effects observed suggest there is more mass present, leading to the conclusion that dark matter must exist.

D. They observe gravitational lensing bending the light of other objects in space. Gravitational lensing occurs when massive objects (like galaxy clusters) bend the path of light from objects behind them. The amount of bending can be used to infer the mass of the foreground object, and observations often reveal more mass than what is visible, again suggesting the presence of dark matter.

While options A and C do reference interesting phenomena, they are not the primary evidence for dark matter's existence. Thus, the best answers would be B and D.