What observations suggest the mass of the Galaxy goes much farther out than its visible disc?
A) the rotation curve of the outermost portions of the disc
B) infrared observations of distant brown dwarfs
C) the orbits of the open clusters in the disc
D) 21- cm maps of the spiral arms
E) X- ray images of other galaxies' discs from Chandra

Question

Quizplus · Accepted Answer

The rotation curve of the outermost portions of the disc suggests the mass of the Galaxy extends much farther than its visible disc. This is because the outer parts of the galaxy rotate at a speed not consistent with the visible mass alone, implying the presence of additional, unseen mass (dark matter) extending beyond the visible boundaries.

What Observations Suggest the Mass of the Galaxy Goes Much