The discoveries of the white dwarf, the neutron star, and the black hole, coming well after the discovery of the...
GMAT Reading Comprehension : (RC) Questions
The discoveries of the white dwarf, the neutron star, and the black hole, coming well after the discovery of the red giant are among the most exciting developments in decades because they may be well present physicists with their greatest challenge since the failure of classical mechanics. In the life cycle of the star, after all of the hydrogen and helium fuel has been burned, the delicate balance between the outer nuclear radiation pressure and the stable gravitational force becomes disturbed and slow contraction begins. As compression increases, a very dense plasma forms. If the initial star had mass of less than 1.4 solar masses (1.4 times the mass of our sun), the process ceases at the density of 1,000 tons per cubic inch, and the star becomes the white dwarf. However, if the star was originally more massive, the white dwarf plasma can't resist the gravitational pressures, and in rapid collapse, all nuclei of the star are converted to a gas of free neutrons. Gravitational attraction compresses this neutron gas rapidly until a density of 10 tons per cubic inch is reached; at this point the strong nuclear force resists further contraction. If the mass of the star was between 1.4 and a few solar masses, the process stops here, and we have a neutron star.
But if the original star was more massive than a few solar masses, even the strong nuclear forces cannot resist the gravitational crunch. The neutrons are forced into one another to form heavier hadrons and these in turn coalesce to form heavier entities, of which we as yet know nothing. At this point, a complete collapse of the stellar mass occurs; existing theories predict a collapse to infinite density and infinitely small dimensions Well before this, however, the surface gravitational force would become so strong that no signal could ever leave the star - any photon emitted would fall back under gravitational attraction – and the star would become black hole in space.
This gravitational collapse poses a fundamental challenge to physics. When the most widely accepted theories predict such improbable things as infinite density and infinitely small dimensions, it simply means that we are missing some vital insight. This last happened in physics in the 1930's, when we faced the fundamental paradox concerning atomic structure. At that time, it was recognized that electrons moved in table orbits about nuclei in atoms. However, it was also recognized that if charge is accelerated, as it must be to remain in orbit, it radiates energy; so, theoretically, the electron would be expected eventually to spiral into the nucleus and destroy the atom. Studies centered around this paradox led to the development of quantum mechanics. It may well be that an equivalent t advance awaits us in investigating the theoretical problems presented by the phenomenon of gravitational collapse.
The primary purpose of the passage is to
1. Passage Analysis:
Progressive Passage Analysis
| Text from Passage | Analysis |
|---|---|
| The discoveries of the white dwarf, the neutron star, and the black hole, coming well after the discovery of the red giant are among the most exciting developments in decades because they may be well present physicists with their greatest challenge since the failure of classical mechanics. | What it says: Scientists recently discovered three types of stars (white dwarf, neutron star, black hole) that are creating major challenges for physics. What it does: Sets up the main topic and establishes importance/significance Source/Type: Author's opinion about significance Connection to Previous Sentences: This is our opening - establishes the framework for everything to follow Visualization: Timeline: Red giant discovered first → Then white dwarf, neutron star, black hole → These new discoveries = biggest physics challenge in decades What We Know So Far: Three stellar discoveries are challenging physics What We Don't Know Yet: What these stars are, why they're challenging, how they relate to each other |
Main Point:
The theoretical problems created by black hole formation represent an exciting opportunity for physics to make major advances, just as previous theoretical crises have led to breakthrough discoveries like quantum mechanics.
• The passage doesn't offer new explanations - it describes accepted scientific understanding of stellar evolution
• The author presents established facts about how stars become white dwarfs, neutron stars, and black holes
• No original theories or novel explanations are proposed
• While the passage does explain these stellar objects, this explanation serves a larger purpose
• The detailed stellar evolution description is not the end goal but supports the argument about theoretical challenges
• The passage spends equal time on the theoretical implications and historical parallels
• The atomic structure discussion is only a brief historical parallel, not a comparison of structures
• The passage doesn't compare atomic and solar system structures at all
• The 1930s atomic paradox is mentioned to show how theoretical crises lead to breakthroughs, not to compare structures
• The passage opens by stating these discoveries "present physicists with their greatest challenge since the failure of classical mechanics"
• The detailed stellar evolution explanation shows how black hole formation creates theoretical problems
• The author explicitly states that theories predicting "infinite density and infinitely small dimensions" means "we are missing some vital insight"
• The historical parallel to the 1930s atomic paradox reinforces how theoretical challenges drive scientific progress
• The imbalance between radiation pressure and gravitational force is mentioned only briefly at the beginning
• This imbalance is just the starting point for stellar collapse, not the main focus
• The passage moves quickly past this concept to focus on the resulting theoretical challenges