Photons cannot escape from the surface of a 

Options

A. white dwarf
B. red giant
C. pulsar
D. black hole

Explanation

To solve the question "Photons cannot escape from the surface of a:", we need to analyze the options given: white dwarf, red giant, pulsar, and black hole.

### Step-by-Step Solution:

**Step 1: Understand the Concept of Photon Escape**
- Photons are particles of light that can escape from a gravitational field if the gravitational pull is not strong enough to trap them. The ability of photons to escape depends on the mass and density of the object they are near.

**Step 2: Analyze Each Option**
- **White Dwarf**: A white dwarf is the remnant of a star that has exhausted its nuclear fuel. It has a high density but is not massive enough to prevent photons from escaping. Therefore, photons can escape from a white dwarf.

- **Red Giant**: A red giant is a star that has expanded and cooled after exhausting its hydrogen fuel. It has a large volume but relatively lower mass compared to other stellar remnants. Thus, photons can escape from a red giant.

- **Pulsar**: A pulsar is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation. While pulsars are dense, they do not have the extreme gravitational pull necessary to trap photons. Therefore, photons can escape from a pulsar.

- **Black Hole**: A black hole is an object with an extremely strong gravitational pull, resulting from a massive star collapsing into a very small volume. The gravitational field of a black hole is so intense that nothing, not even photons, can escape from it.

**Step 3: Conclusion**
- Based on the analysis, the only object from which photons cannot escape is a **black hole**. Therefore, the correct answer is **black hole**.

### Final Answer:
Photons cannot escape from the surface of a **black hole**.

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