Which of the following statements about black holes is not true?

• A. Black holes can be detected by observing the gravitational effects they have on nearby objects.
• B. Black holes emit large amounts of visible light from their interiors.
• C. Nothing, not even $\mathrm{light}$, can escape from within the $\mathrm{event} \mathrm{horizon}$ of a black hole.
• D. The mass of a black hole can be measured by studying the motion of objects orbiting it.

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the nature of black holes. Black holes are regions in space where gravity is so strong that nothing, not even light, can escape once it crosses the event horizon.
2. Step 2: Analyze the statement about black holes emitting large amounts of visible light from their interiors. Since light cannot escape from inside the event horizon, black holes themselves do not emit visible light from their interiors.
3. Step 3: Consider how black holes are detected. They are often detected by observing the gravitational effects on nearby objects, such as stars orbiting an invisible mass or gas emitting X-rays as it heats up near the black hole.
4. Step 4: Review the statement about measuring the mass of a black hole. The mass can indeed be measured by studying the motion of objects orbiting the black hole, using principles from orbital mechanics and gravity.
5. Step 5: Conclude that the incorrect statement is the one claiming black holes emit large amounts of visible light from their interiors, as this contradicts the fundamental property of the event horizon preventing light from escaping.