What observational evidence supports the conclusion that most of the mass of the Milky Way is in the form of dark matter? Although dark matter emits no visible light, we have detected it with radio telescopes. The orbital speeds of stars and gas clouds far from the galactic center are surprisingly high, suggesting that these stars and gas clouds are feeling gravitational effects from unseen matter. There is no observational evidence; it is only a theoretical idea based on computer models indicating that the Milky Way could not have formed unless it had much more mass than it contains in stars and gas. They have directly seen dark matter with no guess work.

Sally turns on her cellular telephone to speak to her friend who is located thousands of miles away. which of the following best describes how such a telephone is able to transmit and receive information? a. the cellular telephone transmits, receives, and encodes information using only sound waves. b. the cellular telephone transmits, receives, and encodes information using only electromagnetic waves. c. the cellular telephone transmits information by electromagnetic waves to a receiver which then encodes them and produces sound. d. the cellular telephone transmits information by sound waves to a receiver which then encodes them and produces electromagnetic waves.