LSAT 107 | Section 4 | Logical Reasoning: Q23

LR Question 23 Explanation

QUESTION TEXT: Quasars-celestial objects so far away that their…

QUESTION TYPE: Must be True

FACTS:

1. Quasars have been seen since 1963.
2. Their light takes 500 million years to reach us.
3. For anything that far away to send light to us it would have to burn with the brightness of 90 billion suns (wow.)
4. Anything that burns that bright will burn out after about 100 million years.

ANALYSIS: We can conclude that any Quasar we see has already burned out. It takes 500 million years for their light to reach us, but they burn out after only 100 million years.

___________

1. We have no idea why nobody saw Quasars before then. Maybe nobody was looking.
2. We don’t know. The light might have been there before but we never noticed.
3. This is tempting, but not true. It’s only true for anything as bright as a quasar and as far away as a Quasar. The sun looks brighter than a quasar even though it doesn’t burn as bright (it’s closer.)
4. Also false. Something could exist longer than a quasar if it didn’t burn as bright as a quasar.
5. CORRECT. Quasars are all burnt out by the time their light reaches us.