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

Question

Quizplus · Accepted Answer

The rotation curve of the outermost portions of the disk suggests that the mass of the Galaxy goes much farther out than its visible disk. The rotation curve shows that the orbital velocity of stars does not decrease as expected with distance from the center, indicating that there must be more mass present beyond the visible disk. This is known as dark matter. The other options do not provide evidence for the mass of the Galaxy extending beyond its visible disk. The rotation curve of the outermost portions of the disk suggests that the mass of the Galaxy goes much farther out than its visible disk. This is because the rotation curve shows that the rotation speed of stars in the outermost parts of the disk does not decrease as expected based on the visible mass. This implies the presence of additional mass that is not visible, likely in the form of dark matter, extending far beyond the visible disk of the Galaxy.

What Observations Suggest the Mass of the Galaxy Goes Much