Question

What observation of the Milky Way Galaxy suggests that it contains a large amount of matter not in the form of stars?

(a)The age of the globular clusters

(b)The shape of the spiral arm

(c)The galactic rotation curve

(d)Infrared observations of the centre of the Galaxy

Please explain briefly why, thanks

Answer 1

Answer :-

The right answer is (c) The galactic rotation curve.

This is because the stars and gases at a wide range of distances from the Galactic Center orbit at approximately 220 kilometers per second. The constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much (about 90%) of the mass of the Milky Way is invisible to telescopes, neither emitting nor absorbing electromagnetic radiation. This conjectural mass has been termed "dark matter".[