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Difficulty: HardBridging Gap (Supporter) Assumptions

Astrophysicist: According to leading cosmological models, a spiral galaxy can maintain its structural integrity over billions of years only if it is enveloped by a massive dark matter halo. The recently observed spiral galaxy VCC-128 has maintained its structural integrity for at least four billion years. Yet, advanced sensor arrays have confirmed that VCC-128 emits no anomalous axion radiation. Therefore, the leading cosmological models must be incorrect.

Which one of the following is an assumption on which the astrophysicist's argument depends?

  1. A
    Spiral galaxies that fail to maintain their structural integrity over billions of years are not enveloped by massive dark matter halos.
  2. B
    Anomalous axion radiation is emitted only by galaxies that are enveloped by a massive dark matter halo.
  3. Any galaxy that is enveloped by a massive dark matter halo emits anomalous axion radiation.Answer
  4. D
    Cosmological models other than the leading ones do not require massive dark matter halos to explain the structure of spiral galaxies.
  5. E
    Advanced sensor arrays are capable of detecting all forms of radiation that might be emitted by a spiral galaxy.

Answer

The correct answer is the statement that any galaxy enveloped by a massive dark matter halo emits anomalous axion radiation.
The correct answer bridges the logical gap between the evidence (no anomalous axion radiation) and the conclusion (models requiring dark matter halos are incorrect). For the absence of axion radiation to invalidate a model requiring a dark matter halo, it must be true that a dark matter halo inherently produces such radiation. If this assumption were false, VCC-128 could possess a dark matter halo despite lacking axion radiation, rendering the argument's conclusion completely unsupported.

Step-by-Step Solution

1
Identify the argument's premises.
Premise 1: Leading models require a massive dark matter halo for a spiral galaxy to maintain integrity. Premise 2: VCC-128 maintains integrity. Premise 3: VCC-128 emits no anomalous axion radiation.
Understanding the core evidence is the first step in analyzing logical gaps.
2
Identify the argument's conclusion.
Conclusion: The leading cosmological models must be incorrect.
Locating the conclusion highlights what the author is trying to prove.
3
Locate the conceptual gap between the premises and the conclusion.
The models deal with 'massive dark matter halos', but the final evidence involves 'anomalous axion radiation'. The author jumps from the absence of axion radiation to the absence of a dark matter halo (which would invalidate the models).
Supporter assumptions always link rogue elements in the premises to elements in the conclusion.
4
Formulate the required bridging assumption.
The argument must assume that having a massive dark matter halo guarantees the emission of anomalous axion radiation (Halo -> Axion).
This bridge ensures that the lack of axion radiation logically proves the lack of a dark matter halo.
5
Apply the Negation Test to confirm the assumption.
Negating the correct statement yields: 'A massive dark matter halo does NOT necessarily emit anomalous axion radiation.' If this is true, VCC-128 could have a halo without emitting axions, entirely destroying the conclusion that the models are incorrect.
The Negation Test is the definitive method for proving a necessary assumption.

Key Concept

Bridging Gap (Supporter) Assumptions
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Topics

Bridging Gap (Supporter) Assumptions

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