Analysis of the motions of stars in the vicinity of the Sun indicates

­8. The author's main point is that

Explanation

The passage argues that a significant portion of the unseen mass in the solar neighborhood might be explained by stellar remnants, particularly those left behind by stars at least ten times as massive as the Sun. The author supports this by suggesting that although the formation of massive stars doesn't predominate at present, it might have been more important in the past when the interstellar gas and star formation rates were greater. Remnants of earlier generations of massive stars could then contribute to the total mass in the solar neighborhood. This aligns with option D.

A. While the passage discusses the possibility that brown dwarfs might not account for the unseen mass, the main focus is on the alternative explanation of stellar remnants, particularly those from massive stars.

B. The passage mentions that Schmidt's model, like an earlier model, assumes a higher ratio of massive stars to smaller stars at earlier times. However, the primary focus is on the potential contribution of stellar remnants to the unseen mass, not the agreement with the conventional view.

C. The passage doesn't suggest that Schmidt's model is based on an improbable assumption. In fact, it indicates that both Schmidt's model and an earlier model share the assumption of a higher ratio of massive stars to smaller stars at earlier times.

E. While the passage supports the idea that stellar remnants are the result of the collapse of massive stars, it doesn't explicitly state the specific mass threshold of ten times as massive as the Sun. The focus is more on the potential contribution of remnants to the unseen mass.

Answer: D