Many disk galaxies, such as Andromeda and the Milky Way, are thought to have extended halos of dark matter because the disk circular orbital speed is observed to ____________ increasing distances from the disk center.
A)stay constant with
B)decrease with
C)be totally absent at

Question

Quizplus · Accepted Answer

The observed circular orbital speeds in disk galaxies like Andromeda and the Milky Way stay roughly constant even at increasing distances from the disk center, which is unexpected under Newtonian dynamics assuming only the visible matter contributes to the galaxy's mass. This discrepancy is one of the key pieces of evidence for the existence of dark matter halos surrounding these galaxies.

Many Disk Galaxies, Such as Andromeda and the Milky Way