GRE Reading Comprehension
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Source: BOOST
It is now established that the Milky Way is far more extended and of much greater mass than was hitherto thought. However, all that is visible of the constituents of the Milky Way's corona (outer edge), where much of the galaxy's mass must be located, is a tiny fraction of the corona's mass. Thus most of the Milky Way's outlying matter must be dark.
Why? Three facts are salient. First, dwarf galaxies and globular clusters, into which most of the stars of the Milky Way's corona are probably bound, consist mainly of old stars. Second, old stars are not highly luminous. Third, no one has detected in the corona the clouds of gaseous matter such as hydrogen and carbon monoxide that are characteristic of the bright parts of a galaxy. At present, therefore, the best explanation-though still quite tentative-for the darkness of the corona is that the corona is composed mainly of old, burned-out stars.
The passage presents which of the following as incontrovertible?
I. The low luminosity of old stars
II. The absence of clouds of gaseous matter from the corona of the Milky Way
III. The predominance of globular clusters and dwarf galaxies in the corona of the Milky Way
- A I only
- B III only
- C I and II only
- D II and III only
- E I, II, and III