Upwards of a billion stars in our galaxy have burnt up their internal energy sources, and so can no longer produce the heat a star needs to oppose the inward force of gravity. These stars, of more than a few solar masses, evolve, in general, much more rapidly than does a star like the Sun. Moreover, it is just these more massive stars whose collapse does not halt at intermediate stages (that is, as white dwarfs or neutron stars). Instead, the collapse continues until a singularity (an infinitely dense concentration of matter) is reached .

It would be wonderful to observe a singularity and obtain direct evidence of the undoubtedly bizarre phenomena that occur near one. Unfortunately in most cases a distant observer cannot see the singularity; outgoing light rays are dragged back by gravity so forcefully that even if they could start out within a few kilometers of the singularity, they would end up in the singularity itself.

25. The author's primary purpose in the passage is to

(A) describe the formation and nature of singularities
(B) explain why large numbers of stars become singularities
(C) compare the characteristics of singularities with those of stars
(D) explain what happens during the stages of a singularity's formation
(E) imply that singularities could be more easily studied if observers could get closer to them



26. The passage suggests which of the following about the Sun?

I. The Sun could evolve to a stage of collapse that is less dense than a singularity.
II. In the Sun, the inward force of gravity is balanced by the generation of heat.
III. The Sun emits more observable light than does a white dwarf or a neutron star.

(A) I only
(B) III only
(C) I and II only
(D) II and III only
(E) I, II, and III



27. Which of the following sentences would most probably follow the last sentence of the passage?

(A) Thus, a physicist interested in studying phenomena near singularities would necessarily hope to find a singularity with a measurable gravitational field.
(B) Accordingly, physicists to date have been unable to observe directly any singUlarity.
(C) It is specifically this startling phenomenon that has allowed us to codify the scant information currently available about singularities.
(D) Moreover, the existence of this extraordinary phenomenon is implied in the extensive reports of several physicists.
(E) Although unanticipated, phenomena such as these are consistent with the structure of a singularity.