Question

What would you conclude about a galaxy whose rotation curve rises steadily with distance beyond the visible part of its disk?

a) The galaxy contains a large amount of visible matter in its outer regions.
b) The galaxy's rotation curve is typical and follows the expectations of visible matter distribution.
c) The galaxy is likely to have an underestimation of its visible matter, and there may be dark matter present.
d) The galaxy is experiencing a unique, unexplained phenomenon.

Answer 1

The rising rotation curve beyond the visible disk of a galaxy suggests that there is dark matter present, contributing to the galaxy's mass and leading to a high mass-to-light ratio.

Step-by-step explanation:

If a galaxy's rotation curve rises steadily with distance beyond the visible part of its disk, the conclusion is that the galaxy is likely to have an underestimation of its visible matter, and there may be dark matter present. This conclusion is supported by the observation that the rotational velocity (or orbital speed) does not decrease with distance from the center, which contradicts the expectation if only visible matter were present. The continued high rotational speed suggests the existence of a halo of dark matter surrounding the luminous parts of the galaxy, extending much farther out than the visible components. This presence of dark matter contributes additional mass that is not accounted for by the luminosity of the galaxy, leading to a high mass-to-light ratio.