QuestionAugust 25, 2025

Fifteen years ago, we observed a quasar that was found to be located 8 billion light years away. The quasar appeared to be 5 million years old. If our Universe is approximately 15 billion years old when did the quasar emit the light that we observed? 15 years ago 5 million years ago 8 billion years ago 15 billion years ago

Fifteen years ago, we observed a quasar that was found to be located 8 billion light years away. The quasar appeared to be 5 million years old. If our Universe is approximately 15 billion years old when did the quasar emit the light that we observed? 15 years ago 5 million years ago 8 billion years ago 15 billion years ago
Fifteen years ago, we observed a quasar that was found to be located 8 billion light years away. The quasar
appeared to be 5 million years old. If our Universe is approximately 15 billion years old when did the quasar emit
the light that we observed?
15 years ago
5 million years ago
8 billion years ago
15 billion years ago

Solution
4.5(177 votes)

Answer

7 billion years ago Explanation 1. Determine the age of the Universe when light was emitted Subtract the distance in light years from the current age of the Universe: 15 \text{ billion years} - 8 \text{ billion years} = 7 \text{ billion years}. 2. Calculate the time when the quasar emitted the light Subtract the age of the quasar from the result in Step 1: 7 \text{ billion years} - 5 \text{ million years}. Since 5 million years is negligible compared to billions, it remains approximately 7 \text{ billion years}.

Explanation

1. Determine the age of the Universe when light was emitted<br /> Subtract the distance in light years from the current age of the Universe: $15 \text{ billion years} - 8 \text{ billion years} = 7 \text{ billion years}$.<br />2. Calculate the time when the quasar emitted the light<br /> Subtract the age of the quasar from the result in Step 1: $7 \text{ billion years} - 5 \text{ million years}$. Since 5 million years is negligible compared to billions, it remains approximately $7 \text{ billion years}$.
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