Section 15 P4 Masses and Distances of Galaxies

Question 1

Realize what it means for stars to be going fast around a galaxy. If the stars in one galaxy are moving extremely fast, what does that tell us about how heavy the galaxy’s mass must be?

Answer 1

Heavy - great mass

Question 2

Recognize the speed of rotation of a galaxy is measured using redshifts and blueshifts of light from parts of a galaxy that are rotating toward us or away from us.

Answer 2

redshift - away

blueshift - closer

Question 3

If astronomers plot the “rotation curve” for a galaxy, this means they plot how the speeds of stars are different as you look at stars ____

Answer 3

further and further from the center of the galaxy.

Question 4

If the rotation curve stays high and “flat” even for objects orbiting out past the visible edge of the galaxy, it means

Answer 4

there is extra material beyond that edge that we are failing to see (dark matter).